IB Biology markscheme, past exam papers, notes and 2012 IB Biology syllabus. IB Biology option D evolution markscheme. IB Biology option D evolution notes, IB Biology option D Evolution exam papers, IB Biology option E markscheme, IB Biology option E notes, IB Biology option E Neurobiology papers, IB Biology Option A Human Nutrition and Health syllabus 2012, Stimulus and response, Homologous structures, Pavlov experiments.
IB Biology Option D.2: Species and speciationJason de Nys
1. Speciation occurs through changes in allele frequencies in a population's gene pool over many generations, driven by factors like natural selection, genetic drift, and geographic isolation of populations.
2. Reproductive isolating mechanisms like temporal, ecological, behavioral, and mechanical barriers prevent interbreeding between species and maintain genetic integrity of gene pools.
3. Adaptive radiation and divergent evolution describe how a single ancestral species can evolve into many new species adapted to different ecological niches or environments through natural selection.
This document discusses evidence that supports the theory of evolution, including:
- The fossil record provides evidence of gradual changes in species over millions of years as seen in successive rock layers.
- Similarities in homologous structures across species, like pentadactyl limbs, provide evidence of common ancestry and gradual divergence over time through processes like adaptive radiation.
- Artificial selection through selective breeding demonstrates how organisms can evolve rapidly in response to environmental pressures like those in nature.
Natural selection and speciation are key concepts in evolution. Natural selection is the process by which organisms better adapted to their environment tend to survive and pass on their genes more than others. Over time, this leads to the evolution of new species through mechanisms of reproductive isolation such as genetic drift and non-random mating. Examples of speciation include the St Kilda wren and the Sorbus shrub on the Isle of Arran. Adaptive radiation and genetic changes also drive the formation of new species.
Evolution and Biodiversity,Genetics,Digestive System,EcosystemJenevive Oloroso
This document contains a prayer asking for help with work, concentration, understanding, learning, and a peaceful mind, as well as remembering Jesus. It is a short prayer requesting guidance.
Natural selection can lead to evolution within a species. There are several key factors:
1) There is genetic variation between individuals, caused by mutation, meiosis and sexual reproduction.
2) Individuals compete for limited resources. Those with adaptations that make them better suited to their environment tend to survive and reproduce more.
3) The heritable traits of the most successful individuals become more common in the population over generations through differential reproduction. This can result in changes within the species over time.
Rep isolating mechanism evolution finalNaeem Ahmed
Speciation occurs through reproductive isolation of populations. Isolating mechanisms like geographic barriers, behavioral differences, or incompatible gametes can prevent interbreeding and lead to the evolution of new species over time. Speciation increases biodiversity and is an important part of evolution. Reproductive isolation can have prezygotic causes like differences in mating behaviors, or postzygotic causes if hybrids are inviable or infertile. Examples of speciation include the diverse finch species that evolved on the Galapagos Islands.
The document provides an overview of evolution and evidence that supports the theory of evolution through natural selection. It summarizes key periods in Earth's history from the Precambrian to present day, highlighting important transitional fossils and extinctions. It also describes several lines of evidence that provide support for evolution, including homologous and vestigial structures, embryology, molecular biology, biogeography, and examples of evolution occurring in present-day populations.
Guided notes covering material from Topics 5.1 and 5.2 of the updated IB Biology syllabus for 2016 exams. Notes sequence and prompts are based on the Oxford IB Biology textbook by Allott and Mindorff.
IB Biology Option D.2: Species and speciationJason de Nys
1. Speciation occurs through changes in allele frequencies in a population's gene pool over many generations, driven by factors like natural selection, genetic drift, and geographic isolation of populations.
2. Reproductive isolating mechanisms like temporal, ecological, behavioral, and mechanical barriers prevent interbreeding between species and maintain genetic integrity of gene pools.
3. Adaptive radiation and divergent evolution describe how a single ancestral species can evolve into many new species adapted to different ecological niches or environments through natural selection.
This document discusses evidence that supports the theory of evolution, including:
- The fossil record provides evidence of gradual changes in species over millions of years as seen in successive rock layers.
- Similarities in homologous structures across species, like pentadactyl limbs, provide evidence of common ancestry and gradual divergence over time through processes like adaptive radiation.
- Artificial selection through selective breeding demonstrates how organisms can evolve rapidly in response to environmental pressures like those in nature.
Natural selection and speciation are key concepts in evolution. Natural selection is the process by which organisms better adapted to their environment tend to survive and pass on their genes more than others. Over time, this leads to the evolution of new species through mechanisms of reproductive isolation such as genetic drift and non-random mating. Examples of speciation include the St Kilda wren and the Sorbus shrub on the Isle of Arran. Adaptive radiation and genetic changes also drive the formation of new species.
Evolution and Biodiversity,Genetics,Digestive System,EcosystemJenevive Oloroso
This document contains a prayer asking for help with work, concentration, understanding, learning, and a peaceful mind, as well as remembering Jesus. It is a short prayer requesting guidance.
Natural selection can lead to evolution within a species. There are several key factors:
1) There is genetic variation between individuals, caused by mutation, meiosis and sexual reproduction.
2) Individuals compete for limited resources. Those with adaptations that make them better suited to their environment tend to survive and reproduce more.
3) The heritable traits of the most successful individuals become more common in the population over generations through differential reproduction. This can result in changes within the species over time.
Rep isolating mechanism evolution finalNaeem Ahmed
Speciation occurs through reproductive isolation of populations. Isolating mechanisms like geographic barriers, behavioral differences, or incompatible gametes can prevent interbreeding and lead to the evolution of new species over time. Speciation increases biodiversity and is an important part of evolution. Reproductive isolation can have prezygotic causes like differences in mating behaviors, or postzygotic causes if hybrids are inviable or infertile. Examples of speciation include the diverse finch species that evolved on the Galapagos Islands.
The document provides an overview of evolution and evidence that supports the theory of evolution through natural selection. It summarizes key periods in Earth's history from the Precambrian to present day, highlighting important transitional fossils and extinctions. It also describes several lines of evidence that provide support for evolution, including homologous and vestigial structures, embryology, molecular biology, biogeography, and examples of evolution occurring in present-day populations.
Guided notes covering material from Topics 5.1 and 5.2 of the updated IB Biology syllabus for 2016 exams. Notes sequence and prompts are based on the Oxford IB Biology textbook by Allott and Mindorff.
This document summarizes isolating mechanisms - factors that prevent gene exchange between populations. There are prezygotic mechanisms, which act before fertilization, including habitat isolation where species occupy different habitats, seasonal isolation with differences in breeding times, and behavioral isolation from variations in courtship displays. Postzygotic mechanisms occur after fertilization, such as gametic mortality where sperm are killed before reaching eggs, hybrid inviability where zygotes do not develop, and hybrid sterility where offspring are viable but infertile. Isolating mechanisms have a genetic basis and act together to maintain species boundaries where populations meet.
This document discusses several topics related to speciation and the evolution of new species:
1. It defines speciation as the development of a new species and examines different species concepts, barriers to reproduction between species, and modes of speciation such as allopatric and sympatric speciation.
2. It explores mechanisms that can lead to reproductive isolation between populations like prezygotic barriers like habitat isolation and postzygotic barriers like hybrid sterility.
3. It discusses examples of allopatric speciation driven by geographic barriers and sympatric speciation driven by mechanisms like polyploidy, habitat differentiation, and sexual selection.
This document provides an outline and content for a lecture on the genetic basis of evolution. The key points covered include:
- Genetic drift and natural selection both influence evolution but selection does not explain everything, as the "pan-selectionist" view suggests.
- Genetic drift, the random changes in allele frequencies between generations due to chance events, is an important evolutionary process that occurs in all populations. It accounts for genetic differences between individuals, populations, and species.
- Other topics that will be covered include defining terms like genes, loci, alleles, genotypes and phenotypes, and exploring the concepts of genetic drift and natural selection in more detail. The goal is to move beyond a "just-so"
This document discusses speciation and the evolution of new species. It defines different types of speciation, including allopatric, parapatric, and sympatric speciation. Reproductive isolation is a key factor in speciation, with both prezygotic barriers that prevent interbreeding and postzygotic barriers affecting the viability of hybrid offspring. Speciation occurs over long periods of time through either gradual evolution or punctuated equilibrium. The document also covers taxonomy, phylogeny, cladistics, extinction, and adaptive radiation.
The document discusses several species concepts:
- The typological concept views species as fixed types, ignoring variation.
- The biological concept defines species as groups of interbreeding populations reproductively isolated from others.
- The nominalistic concept views species as human constructs rather than natural categories.
It also notes difficulties in applying the biological concept, such as asexual reproduction, similar but isolated species, and ring species where isolation breaks down.
Speciation occurs through geographic or reproductive isolation of populations which allows them to evolve independently. There are two patterns of speciation - anagenesis, where a single lineage gradually transforms into a new species, and cladogenesis, where a parent species branches off into one or more new species. Geographic isolation most commonly occurs when a physical barrier divides a population, exposing each group to different selective pressures. Over time, this can lead to the formation of new species through divergent evolution as the isolated groups become increasingly different from one another.
This document provides evidence for evolution by natural selection from multiple sources, including the fossil record, anatomical record, and molecular record. It discusses several key lines of evidence:
- The fossil record shows changes in organisms over millions of years, with transitional fossils showing links between species.
- Comparative anatomy reveals homologous structures across species that indicate common ancestry, as well as vestigial structures providing evidence of evolutionary change over time.
- Molecular data, such as comparing DNA and protein sequences, provides further support for evolutionary relationships between organisms reflected in their genetic similarities.
The document discusses species and speciation. It defines a species as a group of organisms that can interbreed and produce fertile offspring, but are reproductively isolated from other species. It notes that new species usually develop through either geographical (allopatric) or reproductive (sympatric) isolation. Allopatric speciation occurs when a physical barrier divides a population, causing them to evolve separately. Sympatric speciation can happen within the same area through genetic mutations that lead to reproductive incompatibility.
First year SBC174 Evolution course - week 2
1. NeoDarwinism/ModernSynthesis
2. Major transitions in Evolution
3. Geological Timescales
4. Some drivers of evolution
This document contains an outline for an IB Biology unit on evolution. It includes 17 multiple choice or short answer questions about various topics related to evolution, such as the fossil record providing evidence of evolution, selective breeding demonstrating artificial selection, homologous structures evolving through adaptive radiation, and population divergence leading to speciation. Students are asked to define key terms, describe examples like the evolution of melanistic moths in polluted areas, and explain concepts such as how geographic variation can drive evolutionary change.
This document discusses biological species and speciation. It defines a biological species as members of a population that can breed and produce fertile offspring. It describes reproductive isolating mechanisms that prevent interbreeding between species, including prezygotic mechanisms like behavioral, temporal, ecological, mechanical, and gametic isolation and postzygotic mechanisms like zygotic mortality, hybrid inviability, and hybrid infertility. Speciation occurs through allopatric speciation by physical separation of populations or sympatric speciation within a single population through disruptive selection on extreme traits.
Introduction and importance of biological evolutionbhavnesthakur
The document discusses the evolution and phylogeny of elephants. It describes how early elephant ancestors like Moeritherium evolved from small swamp-dwellers into larger proboscideans over time. Key evolutionary transitions included the development of a proboscis, modification of teeth, and increase in size. The main line of elephant evolution proceeded from Moeritherium to Palaeomastodon to Dienotherium to Tetralophodon to Steglophodon to Mastodon and finally to modern elephants and mammoths. Modern elephants are represented by the African elephant Loxodonta and Asian elephant Elephas.
The document discusses the classification of organisms from the broadest to most specific levels: kingdoms, phyla, classes, orders, families, genera, and species. Organisms are classified based on their cells, anatomy, and ability to breed. The classification system helps determine the scientific name of organisms using their genus and species. As an example, the scientific name of the tiger is provided.
1. Heredity is the transfer of traits from parents to offspring. Variations are differences in traits between individuals of the same species.
2. Mendel conducted experiments on pea plants and determined rules for inheritance through traits being dominant or recessive. He found traits were inherited in predictable ratios.
3. Evidence for evolution includes homologous and analogous structures in different species as well as the fossil record showing changes over time.
The document summarizes Darwin's theory of evolution by natural selection. It discusses key concepts such as overproduction of offspring, the struggle for existence, variations and heredity, survival of the fittest, and the origin of species. It notes criticisms of Darwin's original theory, such as its inability to explain the origin of variations and intermediate forms. The document then outlines processes that can lead to variations, such as mutation and genetic drift. It also discusses inheritance of variations, natural selection maintaining constancy or promoting new species, and speciation occurring due to isolation.
It states that the present day complex plants and animals have evolved from earlier simpler forms of life by gradual changes. SEQUENTIAL EVOLUTION ,DIVERGENT EVOLUTION, Theories of evolution.
Evolution is the process of change over time through natural selection. The document summarizes key evidence and theories of evolution, including:
1. Evidence from the fossil record shows gradual changes in life forms over billions of years. Comparative anatomy and embryology also provide evidence of common descent.
2. Darwin's theory of evolution by natural selection proposed that heritable variations arise by mutation and are selected if they confer a survival or reproductive advantage. This results in adaptation and potentially speciation.
3. Modern theories incorporate genetics and show how variation arises from sexual reproduction, mutation, and recombination of genes, and how selection can change allele frequencies to drive evolution or maintain genetic equilibrium.
This document discusses what constitutes a species and how new species arise through evolution. It notes that determining what is and isn't a distinct species can have economic consequences. A species is typically defined as a group that can interbreed and produce fertile offspring, though this definition has limitations. New species arise through both geographic isolation, which leads to allopatric speciation, and reproductive barriers without geographic isolation, known as sympatric speciation. Intrinsic reproductive isolating mechanisms like differences in courtship behaviors or hybrid infertility play a key role in driving the formation of new species over time.
1) The document discusses factors that can initiate microevolutionary changes by altering gene frequencies in populations. These include mutation, gene flow, natural selection, non-random mating, and genetic drift.
2) Five conditions must be met for a population to maintain Hardy-Weinberg equilibrium: no mutation, random mating, no natural selection, large population size, and no gene flow. Deviations from any of these conditions can lead to evolutionary changes by changing allele and genotype frequencies over time.
3) Specific factors that can drive evolutionary changes include mutation, which introduces new variants; gene flow through migration; natural selection favoring certain genotypes; non-random mating patterns; and genetic drift through random processes in small populations
Animal species in the Rainforests Philippines biodiversity and speciationFrenshey Wee
Tropical rainforests exhibit a vast diversity of plant and animal species. Theories for why the tropics are so diverse include interspecific competition over limited resources leading species to find new niches or become extinct, as well as niche partitioning where species utilize different habitats, foods, behaviors to separate resource use. The document then provides details on many animal species endemic to the Philippines including the Philippine eagle, Draco lizards, Mindoro stripe-faced fruit bat, Palawan bearded pig, and others. It describes their key identifying characteristics and conservation status.
This document summarizes isolating mechanisms - factors that prevent gene exchange between populations. There are prezygotic mechanisms, which act before fertilization, including habitat isolation where species occupy different habitats, seasonal isolation with differences in breeding times, and behavioral isolation from variations in courtship displays. Postzygotic mechanisms occur after fertilization, such as gametic mortality where sperm are killed before reaching eggs, hybrid inviability where zygotes do not develop, and hybrid sterility where offspring are viable but infertile. Isolating mechanisms have a genetic basis and act together to maintain species boundaries where populations meet.
This document discusses several topics related to speciation and the evolution of new species:
1. It defines speciation as the development of a new species and examines different species concepts, barriers to reproduction between species, and modes of speciation such as allopatric and sympatric speciation.
2. It explores mechanisms that can lead to reproductive isolation between populations like prezygotic barriers like habitat isolation and postzygotic barriers like hybrid sterility.
3. It discusses examples of allopatric speciation driven by geographic barriers and sympatric speciation driven by mechanisms like polyploidy, habitat differentiation, and sexual selection.
This document provides an outline and content for a lecture on the genetic basis of evolution. The key points covered include:
- Genetic drift and natural selection both influence evolution but selection does not explain everything, as the "pan-selectionist" view suggests.
- Genetic drift, the random changes in allele frequencies between generations due to chance events, is an important evolutionary process that occurs in all populations. It accounts for genetic differences between individuals, populations, and species.
- Other topics that will be covered include defining terms like genes, loci, alleles, genotypes and phenotypes, and exploring the concepts of genetic drift and natural selection in more detail. The goal is to move beyond a "just-so"
This document discusses speciation and the evolution of new species. It defines different types of speciation, including allopatric, parapatric, and sympatric speciation. Reproductive isolation is a key factor in speciation, with both prezygotic barriers that prevent interbreeding and postzygotic barriers affecting the viability of hybrid offspring. Speciation occurs over long periods of time through either gradual evolution or punctuated equilibrium. The document also covers taxonomy, phylogeny, cladistics, extinction, and adaptive radiation.
The document discusses several species concepts:
- The typological concept views species as fixed types, ignoring variation.
- The biological concept defines species as groups of interbreeding populations reproductively isolated from others.
- The nominalistic concept views species as human constructs rather than natural categories.
It also notes difficulties in applying the biological concept, such as asexual reproduction, similar but isolated species, and ring species where isolation breaks down.
Speciation occurs through geographic or reproductive isolation of populations which allows them to evolve independently. There are two patterns of speciation - anagenesis, where a single lineage gradually transforms into a new species, and cladogenesis, where a parent species branches off into one or more new species. Geographic isolation most commonly occurs when a physical barrier divides a population, exposing each group to different selective pressures. Over time, this can lead to the formation of new species through divergent evolution as the isolated groups become increasingly different from one another.
This document provides evidence for evolution by natural selection from multiple sources, including the fossil record, anatomical record, and molecular record. It discusses several key lines of evidence:
- The fossil record shows changes in organisms over millions of years, with transitional fossils showing links between species.
- Comparative anatomy reveals homologous structures across species that indicate common ancestry, as well as vestigial structures providing evidence of evolutionary change over time.
- Molecular data, such as comparing DNA and protein sequences, provides further support for evolutionary relationships between organisms reflected in their genetic similarities.
The document discusses species and speciation. It defines a species as a group of organisms that can interbreed and produce fertile offspring, but are reproductively isolated from other species. It notes that new species usually develop through either geographical (allopatric) or reproductive (sympatric) isolation. Allopatric speciation occurs when a physical barrier divides a population, causing them to evolve separately. Sympatric speciation can happen within the same area through genetic mutations that lead to reproductive incompatibility.
First year SBC174 Evolution course - week 2
1. NeoDarwinism/ModernSynthesis
2. Major transitions in Evolution
3. Geological Timescales
4. Some drivers of evolution
This document contains an outline for an IB Biology unit on evolution. It includes 17 multiple choice or short answer questions about various topics related to evolution, such as the fossil record providing evidence of evolution, selective breeding demonstrating artificial selection, homologous structures evolving through adaptive radiation, and population divergence leading to speciation. Students are asked to define key terms, describe examples like the evolution of melanistic moths in polluted areas, and explain concepts such as how geographic variation can drive evolutionary change.
This document discusses biological species and speciation. It defines a biological species as members of a population that can breed and produce fertile offspring. It describes reproductive isolating mechanisms that prevent interbreeding between species, including prezygotic mechanisms like behavioral, temporal, ecological, mechanical, and gametic isolation and postzygotic mechanisms like zygotic mortality, hybrid inviability, and hybrid infertility. Speciation occurs through allopatric speciation by physical separation of populations or sympatric speciation within a single population through disruptive selection on extreme traits.
Introduction and importance of biological evolutionbhavnesthakur
The document discusses the evolution and phylogeny of elephants. It describes how early elephant ancestors like Moeritherium evolved from small swamp-dwellers into larger proboscideans over time. Key evolutionary transitions included the development of a proboscis, modification of teeth, and increase in size. The main line of elephant evolution proceeded from Moeritherium to Palaeomastodon to Dienotherium to Tetralophodon to Steglophodon to Mastodon and finally to modern elephants and mammoths. Modern elephants are represented by the African elephant Loxodonta and Asian elephant Elephas.
The document discusses the classification of organisms from the broadest to most specific levels: kingdoms, phyla, classes, orders, families, genera, and species. Organisms are classified based on their cells, anatomy, and ability to breed. The classification system helps determine the scientific name of organisms using their genus and species. As an example, the scientific name of the tiger is provided.
1. Heredity is the transfer of traits from parents to offspring. Variations are differences in traits between individuals of the same species.
2. Mendel conducted experiments on pea plants and determined rules for inheritance through traits being dominant or recessive. He found traits were inherited in predictable ratios.
3. Evidence for evolution includes homologous and analogous structures in different species as well as the fossil record showing changes over time.
The document summarizes Darwin's theory of evolution by natural selection. It discusses key concepts such as overproduction of offspring, the struggle for existence, variations and heredity, survival of the fittest, and the origin of species. It notes criticisms of Darwin's original theory, such as its inability to explain the origin of variations and intermediate forms. The document then outlines processes that can lead to variations, such as mutation and genetic drift. It also discusses inheritance of variations, natural selection maintaining constancy or promoting new species, and speciation occurring due to isolation.
It states that the present day complex plants and animals have evolved from earlier simpler forms of life by gradual changes. SEQUENTIAL EVOLUTION ,DIVERGENT EVOLUTION, Theories of evolution.
Evolution is the process of change over time through natural selection. The document summarizes key evidence and theories of evolution, including:
1. Evidence from the fossil record shows gradual changes in life forms over billions of years. Comparative anatomy and embryology also provide evidence of common descent.
2. Darwin's theory of evolution by natural selection proposed that heritable variations arise by mutation and are selected if they confer a survival or reproductive advantage. This results in adaptation and potentially speciation.
3. Modern theories incorporate genetics and show how variation arises from sexual reproduction, mutation, and recombination of genes, and how selection can change allele frequencies to drive evolution or maintain genetic equilibrium.
This document discusses what constitutes a species and how new species arise through evolution. It notes that determining what is and isn't a distinct species can have economic consequences. A species is typically defined as a group that can interbreed and produce fertile offspring, though this definition has limitations. New species arise through both geographic isolation, which leads to allopatric speciation, and reproductive barriers without geographic isolation, known as sympatric speciation. Intrinsic reproductive isolating mechanisms like differences in courtship behaviors or hybrid infertility play a key role in driving the formation of new species over time.
1) The document discusses factors that can initiate microevolutionary changes by altering gene frequencies in populations. These include mutation, gene flow, natural selection, non-random mating, and genetic drift.
2) Five conditions must be met for a population to maintain Hardy-Weinberg equilibrium: no mutation, random mating, no natural selection, large population size, and no gene flow. Deviations from any of these conditions can lead to evolutionary changes by changing allele and genotype frequencies over time.
3) Specific factors that can drive evolutionary changes include mutation, which introduces new variants; gene flow through migration; natural selection favoring certain genotypes; non-random mating patterns; and genetic drift through random processes in small populations
Animal species in the Rainforests Philippines biodiversity and speciationFrenshey Wee
Tropical rainforests exhibit a vast diversity of plant and animal species. Theories for why the tropics are so diverse include interspecific competition over limited resources leading species to find new niches or become extinct, as well as niche partitioning where species utilize different habitats, foods, behaviors to separate resource use. The document then provides details on many animal species endemic to the Philippines including the Philippine eagle, Draco lizards, Mindoro stripe-faced fruit bat, Palawan bearded pig, and others. It describes their key identifying characteristics and conservation status.
The document discusses microevolution versus macroevolution and the process of speciation. Speciation occurs at the boundary between microevolution within a population and macroevolution leading to new taxonomic groups like species. There are different concepts of what defines a species and barriers that can lead to reproductive isolation and the formation of new species, either when populations are separated geographically (allopatric speciation) or within overlapping populations (sympatric speciation). Evidence suggests speciation may occur gradually over long periods, as proposed by Darwin, or in punctuated bursts alternating with long periods of stasis, as proposed by Gould.
The document discusses speciation and the biological species concept. It describes allopatric and sympatric speciation. Allopatric speciation occurs when a population is geographically isolated into subpopulations that then evolve independently. Sympatric speciation can occur without geographic separation when a subset of a population forms a new species. Reproductive isolation is key to the formation of new species and can arise from prezygotic or postzygotic barriers between populations.
Heliconius butterflies that live in South America exhibit reproductive isolation and assortative mating between closely related species. An experiment showed that males of two Heliconius species, H. cydno and H. melpomene, prefer to mate with females of their own color pattern and mate less often with hybrid females. Hybrids also face natural selection pressures as they are eaten more frequently by predators due to a lack of Müllerian mimicry protection. The reproductive isolation, sexual selection, and natural selection acting on these sympatric butterfly species together lead to their evolution and maintenance as distinct species.
Gene pools and speciation occur as populations become isolated over time. Isolation can be geographic, temporal, or behavioral. Isolated populations diverge genetically as allele frequencies change within each population. Speciation can be gradual, occurring over long periods, or abrupt. Polyploidy, where organisms gain extra sets of chromosomes, has led to speciation in plants like onions through reproductive isolation of populations with different ploidy levels. Selection also changes allele frequencies, with directional selection favoring one trait, stabilizing selection favoring intermediate traits, and disruptive selection favoring extreme traits.
1) Meiosis produces haploid sex cells from diploid body cells, separating homologous chromosome pairs and sister chromatids in two steps.
2) Nondisjunction during meiosis can result in gametes with an abnormal number of chromosomes, potentially leading to conditions like Down syndrome.
3) Complete nondisjunction produces gametes with a full extra set of chromosomes, which if fertilized could result in conditions like triploid syndrome, though these are often fatal in humans. Polyploidy has occurred and been beneficial in some plant species.
The document provides information on biological classification and taxonomy. It begins with an overview of the key characteristics used to classify living things (MRS GREN: movement, respiration, sensitivity, growth, reproduction, excretion, nutrition). It then discusses the three domain system, six kingdoms, and examples of important animal and plant phyla. Specific details are provided on characteristics used to distinguish between major plant and animal phyla. The document also covers binomial nomenclature and provides examples of classification keys.
1. Evolution is the process of change over time from early life forms to today's diversity due to natural selection.
2. Charles Darwin proposed the theory of evolution by natural selection after observing species diversity on the Galapagos Islands and realizing that species evolved over generations to be better suited for their environments.
3. Speciation, the evolution of new species, occurs through mechanisms like reproductive isolation, geographic barriers causing allopatric speciation, or adaptive radiation of a species exploiting new environments.
This document provides an overview of evolutionary biology concepts for an AP Biology exam review. It discusses key figures in the development of evolutionary theory like Charles Darwin and his theory of natural selection. It also covers Darwin's theory of natural selection in more detail, explaining the four main points of his theory. Additionally, the document discusses evidence that supports evolution, such as biogeography, the fossil record, comparative anatomy, and molecular biology. It also explains concepts like genetic drift, gene flow, and speciation. In summary, the document is a review of major topics in evolutionary biology for students preparing to take the AP Biology exam.
Unit 5_Evolution by Natural Selection_Complete.pptxNkosenhle Dube
1. Evidence for evolution comes from fossil records, homologous structures, biogeography, and genetics. Fossil records show changes within groups over time, including the origin of new groups and extinction of species. Homologous structures indicate common ancestry. Biogeography, based on patterns of species distribution, allows inferences about when and where groups evolved.
2. Darwin proposed natural selection to explain evolution. He observed variation within populations, inheritance of traits, overproduction of offspring exceeding environmental carrying capacity, and differential survival based on heritable traits. This leads to accumulation of favorable traits and adaptation to the environment over generations.
3. Isolation of populations through geographic or reproductive barriers can lead to allopatric or symp
The document provides information about the classification of living organisms. It discusses that biologists have created a system to classify organisms based on their similarities and differences, with more similar organisms classified together. It also describes some of the basic classification ranks from domain to species. The purpose of classification is to simplify the study of the diversity of life.
The document discusses key concepts related to evolution including natural selection, descent with modification, mutations, adaptations, genetic variation, genetic drift, microevolution, macroevolution, speciation, and coevolution. It explains how small gradual changes over extremely long periods of time through various evolutionary mechanisms like natural selection can result in major changes within populations and the formation of new species through the process of descent with modification.
Key lecture for the EURO-BASIN Training Workshop on Introduction to Statistical Modelling for Habitat Model Development, 26-28 Oct, AZTI-Tecnalia, Pasaia, Spain
Charles Darwin developed the scientific theory of evolution by natural selection to explain how species change over time through descent with modification from common ancestors. His theory states that genetic variation within species leads to different traits, which are acted on by environmental pressures like competition for resources and predation. Traits that increase survival and reproduction become more common in populations over many generations, resulting in evolution of new species. Darwin provided extensive evidence from biogeography, fossils, embryology and comparative anatomy to support his theory.
1) The document summarizes key concepts from Chapter 22 of Campbell and Reece (2010) on evolution by natural selection, including different types of evidence that support evolution such as fossils, homology, biogeography, and genetics.
2) It discusses Darwin's voyage on the Beagle where he observed adaptations of plants and animals in diverse environments and was influenced by observations of finches in the Galapagos Islands.
3) It describes Darwin's theory of natural selection where individuals with heritable traits that increase survival and reproduction will pass those traits on to more offspring over generations, leading to adaptation and speciation over time.
The document defines a gene pool as the collection of all genes in a population. It discusses how a large gene pool indicates greater genetic diversity and robustness, while a small pool risks reduced fitness and extinction. The document also describes gene pools in crop breeding, noting primary and secondary gene pools, and gives gene pool centres as areas where important crops originated.
1. Evolution occurs through "descent with modification" as organisms adapt to their environment over generations through natural selection.
2. Natural selection leads to populations changing over time as certain inheritable traits leave more offspring than others.
3. Evidence for evolution includes the fossil record, biogeography, comparative anatomy and embryology, and molecular biology.
1) The document discusses evidence for evolution including fossil records, homology, biogeography, and genetics. Fossil records show extinction, origins of new groups, and changes over time.
2) Homology provides evidence of common ancestry through similar structures in different species. Biogeography, such as Darwin's observations of island species, also supports evolution.
3) Darwin developed the theory of evolution by natural selection, which proposes that genetic variations arise by mutation and populations evolve through natural selection of inheritable traits that increase survival and reproduction.
The biological species concept defines a species as a group of organisms that can interbreed and produce fertile offspring. Reproductive isolation prevents different species from successfully interbreeding, through prezygotic barriers like habitat isolation that prevent mating, and postzygotic barriers where hybrid offspring are infertile. Speciation, the formation of new species, occurs through geographic isolation of populations (allopatric speciation) or evolution of reproductive barriers without separation (sympatric speciation).
This document provides an overview of evolution and related concepts. It begins by outlining the key objectives to be covered, which include understanding natural selection, mutation and gene recombination in evolution, the role of natural selection, types of isolation and speciation. It then defines evolution and discusses early theories of evolution. Key concepts like variation, natural selection, isolation and speciation are explained. Evidence for evolution such as paleontology, biogeography, anatomy and molecular biology is summarized. It concludes with classifications of living things and the general process of biological evolution.
This document discusses the concept of biological species and mechanisms of reproductive isolation that can lead to speciation. It defines a biospecies as populations that interbreed and produce viable offspring, but are reproductively isolated from other such groups. Speciation can occur through geographic isolation (allopatric speciation) or within the same area (sympatric speciation) due to changes in chromosomes, anatomy, chemicals, ecology or behavior. The document also discusses challenges in defining species and patterns of evolutionary change, such as phyletic gradualism versus punctuated equilibrium.
This document discusses species concepts and speciation. It defines key terms like phenon, taxon, and category. It describes several species concepts including the typological, nominalistic, and biological species concepts. The biological species concept defines a species as groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups. Speciation occurs through lineage splitting that produces two or more separate species and can be caused by populations becoming isolated geographically, temporally, behaviorally, ecologically, or reproductively.
The document discusses two patterns of speciation: gradualism (anagenesis) in which a species slowly changes over time through natural selection until it is considered a new species, and branching (cladogenesis) in which a species rapidly splits into two or more new species. Branching speciation occurs through geographic isolation of populations followed by the evolution of reproductive barriers between the isolated groups, preventing interbreeding. This process of branching is the basis for biological diversity as it leads to the formation of multiple new species from the original.
1) The study sequenced the COI gene of 321 fish specimens from the South China Sea, identifying 122 species and 1 genus. Intraspecific genetic divergence averaged 0.319% while interspecific divergence between congeneric species was 15.742%, around 50 times higher.
2) Hybridization was detected between Pampus argentenus and P. cinereus. Introgression can cause phylogenic paraphyly.
3) Factors like biological mechanisms, water currents, and lack of gene flow may contribute to fluctuations in intraspecific divergence, particularly in minitypical coastal species. DNA barcoding can help discover new species and biodiversity.
This document discusses species and speciation. It defines a species as a group of organisms capable of interbreeding and producing fertile offspring. Speciation is the process by which one species splits into two reproductively isolated species. There are several mechanisms of speciation, including allopatric speciation which occurs when geographic barriers isolate populations, sympatric speciation which can occur without barriers via mechanisms like host plant shifts, and polyploid speciation which results from chromosome duplication. Reproductive isolating mechanisms that prevent interbreeding between species are important in maintaining species boundaries.
This topic raises some engaging issues of debate concerning the moral justification for exploiting
species and the moral imperative for conserving them. Do other organisms have a right to moral
consideration? How is this justified? Do panda bears have a greater right than lichens? What about the rights
of “pest” or pathogenic organisms? To what extent are these a
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A workshop hosted by the South African Journal of Science aimed at postgraduate students and early career researchers with little or no experience in writing and publishing journal articles.
LAND USE LAND COVER AND NDVI OF MIRZAPUR DISTRICT, UPRAHUL
This Dissertation explores the particular circumstances of Mirzapur, a region located in the
core of India. Mirzapur, with its varied terrains and abundant biodiversity, offers an optimal
environment for investigating the changes in vegetation cover dynamics. Our study utilizes
advanced technologies such as GIS (Geographic Information Systems) and Remote sensing to
analyze the transformations that have taken place over the course of a decade.
The complex relationship between human activities and the environment has been the focus
of extensive research and worry. As the global community grapples with swift urbanization,
population expansion, and economic progress, the effects on natural ecosystems are becoming
more evident. A crucial element of this impact is the alteration of vegetation cover, which plays a
significant role in maintaining the ecological equilibrium of our planet.Land serves as the foundation for all human activities and provides the necessary materials for
these activities. As the most crucial natural resource, its utilization by humans results in different
'Land uses,' which are determined by both human activities and the physical characteristics of the
land.
The utilization of land is impacted by human needs and environmental factors. In countries
like India, rapid population growth and the emphasis on extensive resource exploitation can lead
to significant land degradation, adversely affecting the region's land cover.
Therefore, human intervention has significantly influenced land use patterns over many
centuries, evolving its structure over time and space. In the present era, these changes have
accelerated due to factors such as agriculture and urbanization. Information regarding land use and
cover is essential for various planning and management tasks related to the Earth's surface,
providing crucial environmental data for scientific, resource management, policy purposes, and
diverse human activities.
Accurate understanding of land use and cover is imperative for the development planning
of any area. Consequently, a wide range of professionals, including earth system scientists, land
and water managers, and urban planners, are interested in obtaining data on land use and cover
changes, conversion trends, and other related patterns. The spatial dimensions of land use and
cover support policymakers and scientists in making well-informed decisions, as alterations in
these patterns indicate shifts in economic and social conditions. Monitoring such changes with the
help of Advanced technologies like Remote Sensing and Geographic Information Systems is
crucial for coordinated efforts across different administrative levels. Advanced technologies like
Remote Sensing and Geographic Information Systems
9
Changes in vegetation cover refer to variations in the distribution, composition, and overall
structure of plant communities across different temporal and spatial scales. These changes can
occur natural.
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আমাদের সবার জন্য খুব খুব গুরুত্বপূর্ণ একটি বই ..বিসিএস, ব্যাংক, ইউনিভার্সিটি ভর্তি ও যে কোন প্রতিযোগিতা মূলক পরীক্ষার জন্য এর খুব ইম্পরট্যান্ট একটি বিষয় ...তাছাড়া বাংলাদেশের সাম্প্রতিক যে কোন ডাটা বা তথ্য এই বইতে পাবেন ...
তাই একজন নাগরিক হিসাবে এই তথ্য গুলো আপনার জানা প্রয়োজন ...।
বিসিএস ও ব্যাংক এর লিখিত পরীক্ষা ...+এছাড়া মাধ্যমিক ও উচ্চমাধ্যমিকের স্টুডেন্টদের জন্য অনেক কাজে আসবে ...
This presentation was provided by Steph Pollock of The American Psychological Association’s Journals Program, and Damita Snow, of The American Society of Civil Engineers (ASCE), for the initial session of NISO's 2024 Training Series "DEIA in the Scholarly Landscape." Session One: 'Setting Expectations: a DEIA Primer,' was held June 6, 2024.
it describes the bony anatomy including the femoral head , acetabulum, labrum . also discusses the capsule , ligaments . muscle that act on the hip joint and the range of motion are outlined. factors affecting hip joint stability and weight transmission through the joint are summarized.
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2. • Allele frequency & the gene pool
• Barriers between gene pools
• Polyploidy & speciation
• Allopatric & sympatric speciation
• Adaptive radiation
• Convergent & divergent evolution
• Pace of evolution – gradualism & punctuated
equilibrium
• Transient & balanced polymorphisms
MISS J WERBA – IB BIOLOGY 2
3.
4. D.2.3
• A species is often defined as a group of individuals
that actually or potentially interbreed in nature to
produce viable offspring.
• In this sense, a species is the biggest gene pool
possible under natural conditions.
MISS J WERBA – IB BIOLOGY 4
5. D.2.3
• That definition of a species might seem easy, but it is
not — in nature, there are lots of places where it is
difficult to apply this definition.
• For example, many bacteria reproduce mainly
asexually, by binary fission.
• The definition of a species as a group of
interbreeding individuals cannot be easily applied to
organisms that reproduce only or mainly asexually.
MISS J WERBA – IB BIOLOGY 5
6. D.2.3
• The commonly accepted definition is also difficult to
apply to :
– hybrids - eg. mules
– Cases where it is physically impossible for
members of the same species to mate – eg. Canis
familiaris
MISS J WERBA – IB BIOLOGY 6
7. D.2.3
Species
Breeding Ecological Genetic Evolutionary Cladistic
A group of organisms
Group of organisms A group of organisms sharing a unique A group of organisms
Group of organisms
sharing the same with the same collection of structural that shares a common
capable of breeding
ecological niche karyotype & functional ancestor
characteristics
MISS J WERBA – IB BIOLOGY 7
8.
9. D.2.1
• Modern evolutionists apply concepts in genetics to
explain evolution.
• Individuals who are selected for survival in a species
will reproduce and pass on their genes to the
following generation.
• The alleles present in adapted individuals will
become more common within individuals of that
species.
MISS J WERBA – IB BIOLOGY 9
10. D.2.1
• A gene pool is the sum of all the individual genes in a
given population.
• Within a gene pool, every allele has a particular ratio
or frequency.
• The frequency of an allele is the number of
occurrences of that allele in that population.
MISS J WERBA – IB BIOLOGY 10
11. D.2.1
• Gene pools constantly change:
mutations are always occurring and introducing new
genes into the gene pool.
• Genes that confer a disadvantage are (should be) lost
from the pool by natural selection.
MISS J WERBA – IB BIOLOGY 11
12. D.2.1
• Suppose that the pink
body colour of pigs is
controlled by a single
gene (written as B),
and that a mutation
in this gene results in
brown skin (written
as b).
MISS J WERBA – IB BIOLOGY 12
13. D.2.1
• There are 10
BB bb
individual pigs in the BB BB
population shown bb
BB
• This means there are Bb Bb
20 alleles.
bb BB
• There are 12 B alleles
and 8 b alleles.
MISS J WERBA – IB BIOLOGY 13
14. D.2.1
• The frequencies of
BB bb
the alleles are: BB BB
• 12/20 are B bb
BB Bb Bb
This is a frequency of
0.6
bb BB
• 8/20 are b
This is a frequency of
0.4
• The overall frequency should add up to 1.
MISS J WERBA – IB BIOLOGY 14
15.
16. D.2.2
• Features of a species can change with evolution.
• eg.
• If the habitat for a species of tree-dwelling squirrels
were to change such that there was a decrease in the
number of tree shelters and an increase in the
number of ground shelters, the change
would select for squirrels which could
survive in ground shelters.
MISS J WERBA – IB BIOLOGY 16
17. D.2.2
• The ground dwelling squirrels would survive to
reproduce and pass on their characteristics.
• Those which could not live in ground shelters were
selected against so that their numbers would
gradually decrease in the following generations.
• Over time, the species would evolve from a
population consisting mainly of tree
dwellers to a population consisting
mainly of ground dwellers.
MISS J WERBA – IB BIOLOGY 17
18. D.2.2
• The forces of evolution shape and change the
composition of this gene pool and thus the nature of
the population.
• New combinations of alleles produce unique
genotypes.
• When expressed as phenotypes, these combinations
experience natural selection, which determines
which genes are passed on to the next generation.
• There are different types of selection (D.2.9).
MISS J WERBA – IB BIOLOGY 18
19.
20. D.2.4
• Features of a species can change with evolution.
• eg.
• If the habitat for a species of tree-dwelling squirrels
were to change such that there was a decrease in the
number of tree shelters and an increase in the
number of ground shelters, the change
would select for squirrels which could
survive in ground shelters.
MISS J WERBA – IB BIOLOGY 20
21. D.2.4
• If a species is somehow separated into two groups by
an isolation mechanism or barrier, one species could
potentially diverge into two.
• If the environments on either side of the barrier are
different, each environment will select for a different
set of features.
• The two isolated groups cannot interbreed, so there
is no gene flow between them.
MISS J WERBA – IB BIOLOGY 21
22. D.2.4
• After a long period of isolation and selection, the
groups on either side of the barrier may become so
different that they can no longer interbreed when
put together.
• One species has evolved into two.
MISS J WERBA – IB BIOLOGY 22
23. D.2.4
• The genetic isolation between species can occur in a
number of ways, all the result of reproductive
isolation.
• They can be:
– Pre-zygotic isolation – meaning that the zygotes
are not formed because the gametes never meet
– Post-zygotic isolation – meaning that the zygotes
don’t develop
MISS J WERBA – IB BIOLOGY 23
24.
25. D.2.4
• The two species may have evolved in such a way that
they are active at different times of day or night.
• They may even evolve different reproductive
seasons.
• Thus isolated in time, the two groups are not likely to
interbreed.
MISS J WERBA – IB BIOLOGY 25
26. D.2.4
• The two species occupy different habitats in a
similar region.
• May have been separated by an earthquake or river.
• May be the difference between being ground
dwellers or tree dwellers.
• Thus isolated geographically
and ecologically, the two
groups are not likely to
interbreed.
MISS J WERBA – IB BIOLOGY 26
27. D.2.4
• The two groups may become so different that they
no longer identify with each other’s courtship
behaviour, and therefore cannot interbreed.
• The two groups become so different that they
release slightly different chemical signals
(pheromones), and therefore cannot interbreed.
• Audio and visual mating signals may also change.
MISS J WERBA – IB BIOLOGY 27
28. D.2.4
Different species of bowerbird construct elaborate bowers and decorate them with
different colors in order to woo females. The Satin bowerbird (left) builds a channel
between upright sticks, and decorates with bright blue objects, while the MacGregor’s
Bowerbird (right) builds a tall tower of sticks and decorates with bits of charcoal.
Evolutionary changes in mating rituals, such as bower construction, can contribute to
speciation.
MISS J WERBA – IB BIOLOGY 28
29. D.2.4
• The two groups may become so different that they
can no longer physically interbreed.
• If copulation is prevented, there will be no gene flow
between these two groups.
These damselfly penises illustrate just how
complex insect genitalia may be.
MISS J WERBA – IB BIOLOGY 29
30.
31. D.2.4
• Hybrids are produced but fail to develop to
maturity.
• eg.
– a male horse (2n = 64) and a female donkey
(2n = 62) can mate to produce a mule, but the
mule has 63 chromosomes.
– The chromosomes do not pair up during meiosis
– So the mule is sterile
MISS J WERBA – IB BIOLOGY 31
32. D.2.4
• Hybrids are produced but fail to produce functional
gametes.
• The F1 hybrids are fertile but the F2 generation fail
to develop or are infertile.
MISS J WERBA – IB BIOLOGY 32
33.
34. D.2.6
• Speciation is the process by which one or more
species arise from previously existing species.
• A single species may give
rise to a new species
(intraspecific speciation)
or
• Two different species may give rise to a new species
(interspecific hybridisation)
MISS J WERBA – IB BIOLOGY 34
35. D.2.6
• If intraspecific speciation occurs whilst the
populations are physically separated, it is termed
allopatric speciation.
• If the process of speciation occurs while the
populations are occupying the same geographical
area or range, it is termed sympatric speciation.
MISS J WERBA – IB BIOLOGY 35
36. D.2.6
• Occurs when a geographical barrier produces a
barrier to gene flow because of spatial separation.
• Organisms are unable to meet and reproduce,
leading to reproductive isolation.
• Adaptations to a new environment will change the
allele and genotype frequencies.
• Prolonged separation of populations will lead to two
genetically isolated populations, even if the barrier is
removed.
MISS J WERBA – IB BIOLOGY 36
37. D.2.6
• The barriers could be a mountain range, river, etc
• This means that speciation can also occur through
random forces, rather than through natural
selection.
• A famous example of allopatric speciation is that of
Charles Darwin's Galápagos Finches
MISS J WERBA – IB BIOLOGY 37
39. D.2.6
• Occurs due to variations in the mating habits of a
population within the same geographical area.
• The two species occupy different niches in this
habitat, which can hamper gene flow.
• Prolonged separation of populations will again lead
to two genetically isolated populations, even if the
barrier is removed.
MISS J WERBA – IB BIOLOGY 39
40. D.2.6
• Occurs due to genetic divergence (through
reproductive isolation) of various populations from a
single parent species.
• The two variants inhabit the same geographic
region.
MISS J WERBA – IB BIOLOGY 40
43. D.2.5
• A species is often defined as a group of individuals
that actually or potentially interbreed in nature to
produce viable offspring.
• In this sense, a species is the biggest gene pool
possible under natural conditions.
MISS J WERBA – IB BIOLOGY 43
44. D.2.5
• Condition where the cells of an organism contain
more than two homologous sets of chromosomes.
• eg. eg. salmon
– Triploid (3n)
– Tetraploid (4n)
eg. kiwifruit
– Pentaploid (5n)
– Hexaploid (6n)
– Decaploid (10n) eg. strawberries
MISS J WERBA – IB BIOLOGY 44
45. D.2.5
POLYPLOIDY
& THE GENE POOL
• Polyploidy is a form of sympatric speciation.
• It doesn’t add new genes to the gene pool, but gives
rise to new combinations of genes.
• It involves a single organism or hybridisation
between organisms of a different species.
• Very common in plants.
• Polyploidy in a species results in very quick changes
to gene structure & gene expression.
MISS J WERBA – IB BIOLOGY 45
46. D.2.5
AUTOPOLYPLOIDY
• Autopolyploids are polyploids with multiple
chromosome sets derived from a single species.
• Autopolyploids can arise from a spontaneous,
naturally occurring genome doubling (for example,
the potato).
• Others might form following fusion of 2n gametes
(unreduced gametes).
• Bananas and apples can be found as autotriploids.
MISS J WERBA – IB BIOLOGY 46
47. D.2.5
AUTOPOLYPLOIDY
• Autopolyploids usually have an odd number of sets
of chromosomes.
• They are usually sterile.
MISS J WERBA – IB BIOLOGY 47
48. D.2.5
ALLOPOLYPLOIDY
• Allopolyploids are polyploids with chromosomes
derived from different species.
• It is the result of doubling of chromosome number in
an F1 hybrid (rare: a fertile hybrid)
• Triticale is an example of an allopolyploid, having six
chromosome sets: 4 from wheat and 2from rye.
• The resulting species is infertile with both parent
species.
MISS J WERBA – IB BIOLOGY 48
49.
50. D.2.7
• Adaptive radiation describes the situation in which
homologous structures are differentiated to
perform a variety of different functions.
• Homologous structures have the same genetic basis.
• All organisms that belong to a particular taxonomic
class share a number of modified features, which
adapt them to particular ecological habitats.
MISS J WERBA – IB BIOLOGY 50
54. D.2.8
• Divergent evolution:
when one species evolves into several different
species
• Due to different selection pressures in their
environments.
• It is also known as adaptive evolution.
MISS J WERBA – IB BIOLOGY 54
55. D.2.8
• eg.
Charles Darwin's Galápagos finches proven to have
evolved slightly different beaks due to the nature of
the foods they were eating
MISS J WERBA – IB BIOLOGY 55
56.
57. D.2.8
• Convergent evolution:
when two species evolve similar features if placed in
similar environments
• Due to similar selection pressures in their
environments.
• The examples are actually pretty cool.....
• http://en.wikipedia.org/wiki/List_of_examples_of_co
nvergent_evolution
MISS J WERBA – IB BIOLOGY 57
58. D.2.8
• eg.
The streamlined bodies and fins of sharks (fish) and
dolphins (mammals)
MISS J WERBA – IB BIOLOGY 58
59. D.2.8
• eg.
ant eaters, aardvarks, echidnas and numbats have all
developed claws and sticky, long tongues to open up
termite nests and eat them
MISS J WERBA – IB BIOLOGY 59
60. D.2.8
• eg.
These two succulent plant genera, Euphorbia and
Astrophytum, are only distantly related, but have
independently converged on a very similar body
form.
MISS J WERBA – IB BIOLOGY 60
61. D.2.8
• eg.
The camera eye of cephalopods (e.g. squid) and
vertebrates (e.g. mammals). Their last common
ancestor had at most a very simple photoreceptive
spot, but a range of processes led to the progressive
refinement of this structure to the advanced camera
eye - with one subtle difference; the cephalopod eye
is "wired" in the opposite direction, with blood and
nerve vessels entering from the back of the retina,
rather than the front as in vertebrates
MISS J WERBA – IB BIOLOGY 61
62.
63. D.2.9
• Evolution is a slow process.
• Most of our ideas about evolution are supported by
fossil records, which are incomplete.
• Darwin thought evolution to be a gradual process, a
series of minor changes which, over time, led to a
distinct difference between the individual and its
ancestors.
• Lately, a new idea has come up which, to a certain
extent, explains the inconsistencies of the fossil
record.
MISS J WERBA – IB BIOLOGY 63
64. D.2.9
• In 1972, Eldredge and Gould suggested that
evolution may occur in short periods of rapid
change, followed by long periods of no change.
• The idea is that a large population which experiences
different selection pressures will probably not
change much.
• However, a small population, specially one that
experiences a new environment, could undergo rapid
changes due to selection pressures in a certain
direction. This is called punctuated equillibria.
MISS J WERBA – IB BIOLOGY 64
65. D.2.9
• It is known that some species during certain times
have evolved gradually
(eg. mammals in Africa),
while others seem
to follow the punctuated
equillibria model.
• It is possible that the times of rapid change are
caused by meteor impacts and/or volcanic eruptions
which caused climatic changes.
MISS J WERBA – IB BIOLOGY 65
67. D.2.9
• Stabilising selection:
– Tends to eliminate extreme phenotypes from
populations.
– Maintains phenotypic stability within a population.
• Directional selection:
– A gradual change in the environment moves the
mean phenotype towards a new mean.
– Will continue until the new mean coincides with the
optimum environmental conditions.
MISS J WERBA – IB BIOLOGY 67
68. D.2.9
• Disruptive selection:
– Fluctuating conditions in an environment may favour
the presence of 2 phenotypes in a population.
– May split the population into 2 sub-populations
(? speciation)
MISS J WERBA – IB BIOLOGY 68
69.
70. D.2.10
D.2.11
• If two different variants of a phenotype coexist in the
same population, it is called a balanced
polymorphism.
• eg. Sickle cell anaemia
– Homozygous recessive has SCA, but homozygous dominant
does not
– Heterozygote also shows no symptoms of SCA
– The allele frequency of SCA is maintained by a
heterozygote advantage (can survive malaria)
– Stable frequencies of two or more phenotypic forms are
maintained
MISS J WERBA – IB BIOLOGY 70
71. D.2.10
D.2.11
• If two different variants of a phenotype are in the
process of replacing each other , it is called a
transient polymorphism.
• eg. Peppered moths
– Light coloured moth was once prevalent
– Industrial revolution lead to increased frequency of dark
variant and the decreased frequency of the light variant
MISS J WERBA – IB BIOLOGY 71