This document discusses genetic drift, which refers to random changes in allele frequencies between generations independent of natural selection. Genetic drift has a greater impact in small populations and can lead to the loss or fixation of alleles. The bottleneck effect and founder effect are examples where genetic drift in small populations causes allele frequency changes compared to the original larger population. The neutral theory of evolution proposes that most genetic variation arises from the accumulation of neutral mutations through genetic drift rather than natural selection.
hardy weinberg genetic equilibrium by kk sahuKAUSHAL SAHU
INTRODUCTION
HISTORY
THE HARDY-WEINBERG LAW
DERIVATION
TERMINOLOGY
PROBLEMS
ASSUMPTION OF HAEDY –WEINBERG EQUILIBRIUM
REFERANCE
The Hardy–Weinberg principle, also known as the Hardy–Weinberg equilibrium, model, theorem or law.
States that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.
These influences include mate choice, mutation, selection, genetic drift, gene flow and meiotic drive.
Because one or more of these influences are typically present in real populations, the Hardy–Weinberg principle describes an ideal condition against which the effects of these influences can be analyzed.
Molecular evolution, four class of chromosomal mutation, Negative Selection and Positive Selection, Mutations in DNA and protein, Neutral Theory of Molecular Evolution, Evidence supporting neutral evolution, Phylogenetic trees, Methods of Tree reconstruction
This presentation is uploaded by Mahar Tanvir ul Hassan Tibbi Tarhana Samandry Faisalabad Pakistan. I am enrolled in University of Sargodha in MSc Zoology.
Speciation is the evolutionary process by which reproductively isolated biological populations evolve to become distinct species.There are few mechanisms through which this process can be well understood.
hardy weinberg genetic equilibrium by kk sahuKAUSHAL SAHU
INTRODUCTION
HISTORY
THE HARDY-WEINBERG LAW
DERIVATION
TERMINOLOGY
PROBLEMS
ASSUMPTION OF HAEDY –WEINBERG EQUILIBRIUM
REFERANCE
The Hardy–Weinberg principle, also known as the Hardy–Weinberg equilibrium, model, theorem or law.
States that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.
These influences include mate choice, mutation, selection, genetic drift, gene flow and meiotic drive.
Because one or more of these influences are typically present in real populations, the Hardy–Weinberg principle describes an ideal condition against which the effects of these influences can be analyzed.
Molecular evolution, four class of chromosomal mutation, Negative Selection and Positive Selection, Mutations in DNA and protein, Neutral Theory of Molecular Evolution, Evidence supporting neutral evolution, Phylogenetic trees, Methods of Tree reconstruction
This presentation is uploaded by Mahar Tanvir ul Hassan Tibbi Tarhana Samandry Faisalabad Pakistan. I am enrolled in University of Sargodha in MSc Zoology.
Speciation is the evolutionary process by which reproductively isolated biological populations evolve to become distinct species.There are few mechanisms through which this process can be well understood.
Population genetic analysis, Finding out gene frequencies in a population, description of how Selection, mutation, migration brings a change in allelic frequencies of a population.
Evolution on how Charles Darwin the father of evolution explained the different types of mechanisms of evolution these are by natural selection, genetic drift, gene flow and many more
evolution of human evolution of human evolution of human evolution of human evolution of human evolution of human evolution of human. human evolution human evolution human evolution human evolution . population and evolution population and evolution population and evolution
Evolution in small population
by HAIDER ALI
In biology evolution is the change in the characteristics of a species over several generations and relies on the process of natural selection,
The theory of evolution is based on the idea that all species are related and gradually change.
This is PPT on Evolution. This is just and introductory PPT. Soon There will be a PPT with much more on Evolution. Hope That you all like it. please like and share. each like Counts.
2. Learning Objectives
• Describe the phenomena of the bottleneck
effect and founder effect and explain how
they contribute to changes in allelic
frequencies.
• Explain what is sometimes referred to as
"survival of the luckiest."
3. Genetic Drift
• So far, natural selection was the explanation
for genetic change
• What is genetic drift?
• Changes in allele frequencies due to random
chance
• Observation that by chance, allele frequencies
“drift” from one generation to the next.
4. Genetic Drift
• Allele frequency changes occur regardless of
those allele-carrying individuals and their
fitness.
• For example:
• How is it known which alleles will be in the
gametes that fuse together during
fertilization?
• It’s influenced by random chance!
5. Genetic Drift
• Has a greater impact in small populations
• Effects of Genetic Drift
• Elimination or fixation of an allele
• Depends on if allele frequency reaches 0 or
100%
• Number of generations needed for this
depends on population size
7. Question
• The relative effect of random chance (a.k.a.
random sampling error) is much
smaller/bigger when the sample size is
large/small.
• The relative effect of random chance (a.k.a.
random sampling error) is much smaller when
the sample size is large.
8. Genetic Drift Has a Greater Impact
in Small Populations
• In the end, regardless of population size,
genetic drift = allele loss or fixation
• More generations are needed in large
populations than small ones
• Decrease in population size could allow
genetic drift to alter allele frequencies.
9. Bottleneck Effect
• Different events can get rid of population
members w/out regard to genetic composition
• Events:
earthquakes, floods, drought, human
destruction of habitat
• Bottleneck effect: allele frequencies in a
population change due to genetic drift
10. Bottleneck Effect
• 2 reasons for change:
1. Surviving population members have
different allele frequencies than original
population
2. When population is small, genetic drift
reduces genetic variation faster
a. Alleles could even get eliminated
14. Founder Effect
• Small group of individuals separates from large
population, and establishes a colony in a new
place.
• Ex.) few people leave a population and
become founders of a separate island.
16. Founder Effect
• 2 major consequences:
1. The smaller new population won’t have as much
genetic variation as the original, larger population.
2. The allele frequencies in the new population will be
different than the original population (by chance).
• Ex. of the Founder effect: Old Order Amish population in
Pennsylvania.
• Group of 8,000 people left the original group.
• That newer population had Ellis-van Creveld syndrome
at 7% frequency rate (much higher compared to original
population).
17. The Neutral Theory of
Evolution
• Majority of genetic variation is due to genetic
drift instead of natural selection.
• Reason: genetic drift can affect frequencies
of helpful and detrimental alleles.
• Genetic drift promotes neutral variation, which
does not affect reproductive success.
18. The Neutral Theory of
Evolution
• Neutral theory of Evolution: most genetic
variation is caused by the accumulation of
neutral mutations that got high frequencies
through genetic drift.
• Ex.) a mutation in a gene that changes one
codon won't affect the entire amino acid
sequence of the encoded protein, so both
genotypes are still equal in terms of fitness.
19. The Neutral Theory of
Evolution
• Non-Darwinian evolution: new mutations can spread throughout
a population because of genetic drift.
• a.k.a. "survival of the luckiest".
• Darwin's idea: natural selection is responsible for
adaptive changes during evolution is accepted
• Ex.) giraffes with their long necks
• Kimura's idea: most of DNA sequence variation is due to neutral
variation.
• At the genomic and molecular level, genome sequencing from
different species is consistent with the neutral theory of
evolution.
• Ex.) changes of the coding sequences in structural genes
Editor's Notes
genetic drift is a change in genetic variation from generation to generationallele frequency is a value determined by the number copies of a specific allele divided by the total number of alleles in a population
Figure 24.10 illustrates the potential consequences of genetic drift in one large (N = 1,000) and two small (N = 10) populations. This simulation involves the frequency of hypothetical B and b alleles of a gene for fur color in a population of mice—B is the black allele, and b is the white allele.Genetic drift and population size. This graph shows three hypothetical simulations of genetic drift and their effects on small and large populations of black (B allele) and white (b allele) mice. In all cases, the starting allele frequencies are B = 0.5 and b = 0.5. The red lines illustrate two populations of mice in which N = 10; the blue line shows a population in which N = 1,000. Genetic drift eventually leads to either the elimination or fixation of alleles.At the beginning of this hypothetical simulation, which runs for 50 generations, all of these populations had identical allele frequencies: B = 0.5 and b = 0.5. In the small populations, the allele frequencies fluctuated substantially from generation to generation. Eventually, in one population, the b allele was eliminated, while in another, it was fixed at 100%. These small populations would then consist of only black mice or white mice, respectively. At this point, the gene has become monomorphic and cannot change any further. By comparison, the frequencies of B and b in the large population fluctuated much less.
*do question first, then explain*Reviewing briefly from chapter 16The deviation between the observed and expected outcomes is called the random sampling error. With a small sample, the random sampling error may cause the observed data to be quite different from the expected outcome. By comparison, if we flipped a coin 1,000 times, the percentage of heads would be fairly close to the predicted 50%. With a larger sample, we expect the sampling error to be smaller.
Population of frogs (shown in diagram to the right)Real-life example: the African cheetah population lost almost all genetic variation, probably due to bottleneck effect. Species came back to original numbers, but very low genetic variation
Difference between founder effect and bottleneck effect is that the founder effect occurs in a new location, but both effects are related to a reduction in population size.
-Japanese biologist Motoo Kimura came up with idea of “neutral theory of evolution”-neutral variation does not affect reproductive success
- there are more nucleotides in a codon's 3rd base. 3rd base mutations are usually neutral, compared to the random, more harmful, and more likely to be eliminated mutations at the 1st or 2nd bases.
Neutral evolution in a population. In this example, a mutation within a gene changes a glycine codon from GGG to GGC, which does not affect the amino acid sequence of the encoded protein. Each gene shown represents a copy of the gene in a member of a population. Over the course of many generations, genetic drift may cause this neutral allele to become prevalent in the population, perhaps even monomorphic.
