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Igcse biology edexcel 3.13 3.33

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Edexcell ppt Biology 3.13 - 3.33

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Igcse biology edexcel 3.13 3.33

  1. 1. INHERITANCE (Syllabus points 3.13 – 3.33)
  2. 2. REPRODUCTION (review) 3.1 understand the differences between sexual and asexual reproduction There are two types of reproduction; • Sexual: reproduction in which two gametes (sex cells) fuse to create a new offspring that is genetically different to the parents. Two parents are involved. • Asexual: reproduction without fusion of gametes. It involves one parent only and produces offspring that are genetically identical to the parent (clones).
  3. 3. Fertilization (review) 3.2 understand that fertilisation involves the fusion of a male and female gamete to produce a zygote that undergoes cell division and develops into an embryo Definitions • Fertilization: • Zygote: • Embryo: A male and a female gamete fuse to form a zygote a cell that is the result of fertilization. It will divide by mitosis to form an embryo An organism in its early stages of development, especially before it has reached a distinctively recognizable form.
  4. 4. Fertilization, Zygote, Embryo(Review) 3.2 understand that fertilisation involves the fusion of a male and female gamete to produce a zygote that undergoes cell division and develops into an embryo
  5. 5. Genes are on Chromosomes 3.13 understand that the nucleus of a cell contains chromosomes on which genes are located The nucleus of every cell contains DNA. The DNA is organized in genes and the genes are located on Chromosomes. The best way to think about it is like a library…. video press
  6. 6. 3.13 understand that the nucleus of a cell contains chromosomes on which genes are located LIBRARY Books Chapters Words Letters Nucleus Chromosome (23 pairs) Gene (makes one protein) Group of 3 letters DNA letters (A, C, T, G)
  7. 7. 3.13 understand that the nucleus of a cell contains chromosomes on which genes are located
  8. 8. Genes Make a SPECIFIC Protein 3.14 understand that a gene is a section of a molecule of DNA and that a gene codes for a specific protein 1) Genes are written in DNA code. 2) The code can be translated into amino acids. 3) Amino Acids are linked together to make proteins. ONE Gene codes for ONE specific protein
  9. 9. Genes Make a SPECIFIC Protein 3.14 understand that a gene is a section of a molecule of DNA and that a gene codes for a specific protein A three-base sequence codes for each amino acid. base sequence amino acid
  10. 10. Genes Make a SPECIFIC Protein 3.14 understand that a gene is a section of a molecule of DNA and that a gene codes for a specific protein Genes don’t actually make proteins – they just contain the instructions on how to make them. DNA stays in the nucleus but proteins are built in the cell’s cytoplasm.
  11. 11. 3.14 understand that a gene is a section of a molecule of DNA and that a gene codes for a specific protein So Your Genes code for Your Proteins
  12. 12. WHAT IS DNA? 3.15 describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with thymine (T), and cytosine (C) with guanine (G) DNA is a very long molecule. It is shaped like a twisted ladder. Two long strands make the backbones and are connected by rungs or links.
  13. 13. BASE PAIRS 3.15 describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with thymine (T), and cytosine (C) with guanine (G) The Strands are connected by BASE PAIRS • Adenine (A) • Thymine (T) • Cytosine (C) • Guanine (G) The bases only match: A-T C-G
  14. 14. Genes come in Variations 3.16 understand that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics Sometimes more than one version of a gene occurs. The different versions are called alleles (i.e. we all have the gene for iris pigment (protein), but there are different colours of iris pigment, same gene but different alleles)
  15. 15. Alleles give rise to Variation 3.16 understand that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics over view
  16. 16. Alleles give rise to Variation (2) 3.16 understand that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics Alleles give rise to a range of different inherited characteristics in a population. These can include in humans: Eye Colour Skin Colour Hitch Hikers Thumb Rolling of the tongue Earlobe shape Blood Type Many many others………..
  17. 17. DEFINITIONS OF INHERITANCE TERMS 3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance Dominant: A gene allele that ‘expresses’ over another allele in homozygous and heterozyogus pairs. Shown in phenotype. b B Recessive: A gene allele that only ‘expresses’ when it is matched with another recessive allele and never when matched with a dominant allele. Homozygous Recessive. Shown in phenotype b b
  18. 18. DEFINITIONS OF INHERITANCE TERMS 3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance Homozygous: having identical alleles at corresponding chromosome Loci (Gene Location). Heterozygous: having dissimilar alleles at corresponding chromosomal Loci. b B B B b b
  19. 19. DEFINITIONS OF INHERITANCE TERMS 3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance
  20. 20. DEFINITIONS OF INHERITANCE TERMS 3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance
  21. 21. DEFINITIONS OF INHERITANCE TERMS 3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance Phenotype: the set of observable characteristics Geneotype of an individual resulting from the interaction of its genotype with the environment Genotype: The genetic makeup of a cell, an organism, or an individual with reference to a specific characteristic. Environemnt Phenotype
  22. 22. DEFINITIONS OF INHERITANCE TERMS 3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance
  23. 23. 3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance
  24. 24. DEFINITIONS OF INHERITANCE TERMS 3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and co-dominance Codominance: A single gene has more than one dominant allele and both genes are expressed. The meaning of the prefix "co-" is "together". Cooperate = work together. Coexist = exist together. Cohabitat = habitat together. When writing alleles remember: All alleles are CAPITAL letters *I remember codominance in the form of an example like so: red x ---> r d & h t s o t d
  25. 25. CODOMINANCE
  26. 26. Genetic Diagrams - Generations 3.18 describe patterns of monohybrid inheritance using a genetic diagram Generations There are the parents, then their offspring, and their offspring, etc. etc. Each generation has a name. The first plants or animals bred together are called the Parental generation, or P1 generation. Their offspring are called the First Filial generation, or F1 generation. Their offspring are called the Second Filial generation, or F2 generation. And so on. And so on.
  27. 27. Genetic Diagrams – Punnett Squares 3.18 describe patterns of monohybrid inheritance using a genetic diagram SOME SIMPLE EXAMPLES OF WHAT YOU CAN USE A PUNNETT SQUARE FOR SEED COLOUR FLOWER COLOUR GENDER press
  28. 28. Genetic Diagrams – Punnett Squares 3.18 describe patterns of monohybrid inheritance using a genetic diagram P1 P1 P1 Genotype of F2 press
  29. 29. Genetic Diagrams – Punnett Squares 3.18 describe patterns of monohybrid inheritance using a genetic diagram How to diagram patterns in monohybrid inheritance: 1) Phenotype of Parents P1 2) Genotype of Parents 3) Gametes Produced 4) Genotype of F1 (you may need a Punnett square) 5) Phenotype of F1 6) Gametes from F1 produced 7) Genotype of F2 (you may need a Punnett square) 8) Phenotype of F2 9) What are the ratios of F2 Phenotype and Genotypes
  30. 30. Genetic Diagrams – Crossing 3.18 describe patterns of monohybrid inheritance using a genetic diagram To cross two tall plants 1. The allele for tallness is H and is dominant to that for smallness, h. 2. If the two plants are heterozygous, they will have a genotype, which contains the alleles Hh. 3. Gametes of individuals contain half of the chromosomes. So only one of the alleles will be present in each gamete cell. So there will be 3 tall plants for every 1 small plant. Or to put it another way, there is a 75% chance that each F1 (offspring) plant will be tall. press
  31. 31. TESTCROSS 3.18 describe patterns of monohybrid inheritance using a genetic diagram Geneticists use the testcross to determine unknown Genotypes A testcross can reveal an unknown genotype 1. Mate an individual of unknown genotype and a homozygous-recessive individual 2. In a test cross you breed an organism showing the dominant features with one showing the recessive feature 3. Each of the two possible genotypes (homozygous or heterozygous) gives a different phenotypic ratio in the F1 generation
  32. 32. TESTCROSS 3.18 describe patterns of monohybrid inheritance using a genetic diagram
  33. 33. Pedigree Charts 3.19 understand how to interpret family pedigrees A pedigree is a chart of the genetic history of family over several generations. Constructing a Pedigree • Female • Male Connecting Pedigree Symbols • Married Couple • Siblings • Fraternal twins • Identical twins • Not Affected • Affected • Deceased
  34. 34. Example (Dominant or Recessive) 3.19 understand how to interpret family pedigrees Is the Affected allele Dominant or Recessive? Affected Unaffected aa AA RECESSIVE Aa Aa Aa aa aa aa Aa Aa aa aa aa
  35. 35. Example (Dominant or Recessive) 3.19 understand how to interpret family pedigrees Is the Affected allele Dominant or Recessive? Affected Unaffected Aa aa Aa Aa DOMINANT aa aa Aa Aa Aa AA AA aa Aa
  36. 36. Interpreting a Pedigree Chart (hard) 3.19 understand how to interpret family pedigrees Determine if the pedigree chart shows: • An autosomal disease -The disease Allele is not on Sex Chromosome (X Y) -The disease Allele can be dominant or recessive • X-linked disease -The disease Allele is found on X Sex Chromosome -( X = Normal Allele, Xr = Disease Recessive Allele) press If it is a 50/50 ratio between men and women. The disorder is autosomal. Most of the males in the pedigree are affected. The disorder is X-linked press
  37. 37. Interpreting a Pedigree Chart (additional) 3.19 understand how to interpret family pedigrees Sex Linked diseases can include: • Hemophilia (Xr) - Recessive • Colour blindness (Xr) - Recessive The phenotype of a Carrier is “NOT DISEASED”
  38. 38. Example (Dominant or Recessive) 3.19 understand how to interpret family pedigrees Example of Pedigree Charts • Is the affected trait Autosomal or X-linked? AUTOSOMAL If it is a 50/50 ratio between men and women. The disorder is autosomal.
  39. 39. Example (Dominant or Recessive) 3.19 understand how to interpret family pedigrees Summary • Pedigrees are family trees that explain your genetic history. • Pedigrees are used to find out the probability of a child having a disorder in a particular family. • To begin to interpret a pedigree, determine if the disease or condition is autosomal or X-linked and dominant or recessive.
  40. 40. Monohybrid Cross Probability 3.20 predict probabilities of outcomes from monohybrid crosses GIVE THE GENOTYPE RATIO: GIVE THE GENOTYPE RATIO: GIVE THE PHENOTYPE RATIO:
  41. 41. Male or Female 3.21 understand that the sex of a person is controlled by one pair of chromosomes, XX in a female and XY in a male
  42. 42. Male or Female 3.21 understand that the sex of a person is controlled by one pair of chromosomes, XX in a female and XY in a male XX = Female XY = Male
  43. 43. Determine the Sex (diagram it) 3.22 describe the determination of the sex of offspring at fertilisation, using a genetic diagram
  44. 44. Diploid Cell Division 3.23 understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes
  45. 45. What are homologous chromosomes? 3.23 understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes Different organisms have different numbers of chromosomes. Humans have 46 chromosomes. This is the diploid number of humans. Chromosomes can be grouped in pairs called homologous chromosomes. In each pair, one chromosome has been inherited from the mother and the other inherited from the father. homologous pair chromosome from mother chromosome from father
  46. 46. What are homologous chromosomes? 3.23 understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes 2n Body cells are: 2n - Diploid Sex Cells are: n - Haploid 2n 2n
  47. 47. What is Mitosis good for? 3.24 understand that mitosis occurs during growth, repair, cloning and asexual reproduction MITOSIS GROWTH New cell growth Nerve cells (tissue) Muscle cells (tissue) Repair Scar tissue Replace old cells RBC Skin Cloning Dolly the sheep Asexual Reproduction Budding Bacteria & Yeast Cuttings, Bulbs, Tubers, Runners Willow Tulips Potatoes Strawberries
  48. 48. Meiosis Makes Gametes 3.25 understand that division of a cell by meiosis produces four cells, each with half the number of chromosomes, and that this results in the formation of genetically different haploid gametes
  49. 49. Meiosis Makes Gametes 3.25 understand that division of a cell by meiosis produces four cells, each with half the number of chromosomes, and that this results in the formation of genetically different haploid gametes 3.27 know that in human cells the diploid number of chromosomes is 46 and the haploid number is 23 MITOSIS MEIOSIS 1) Produces 2 daughter cells 2) Daughter cells are diploid (have 23 pairs of chromosomes) 3) Daughter cells are genetically identical to each other. 3) Gametes are different to each other 4) Gametes are different to the parent cell (crossing over of genetic material) 5) Two stage process 6)Happens in Reproductive organs only 4) Daughter cells are genetically identical to the parent cell (no genetic crossing over) 5) One stage process 6) Happens everywhere in the body 1) Produces 4 gamete cells 2) Daughter cells are haploid (Only have 23 chromosomes)
  50. 50. Random Fertilization and Variation 3.26 understand that random fertilisation produces genetic variation of offspring
  51. 51. Key Word basic Summary This topic, more than any other, confuses people. Remember these! DNA: A genetic code Gene: One instruction in the code telling a cell how to make a specific protein Allele: A different version of a gene Chromosome: Coiled up DNA Haploid number: the number of different chromosomes in a cell (23) Diploid number: the total number of chromosomes in a cell (46) Cell Division: There are two types of cell division; - Mitosis – used for growth, repair & asexual reproduction - Meiosis – used to produce gametes for sexual reproduction
  52. 52. Nature Vs Nurture 3.28 understand that variation within a species can be genetic, environmental, or a combination of both Variation
  53. 53. Mutations (not all x-men get superpowers) 3.29 understand that mutation is a rare, random change in genetic material that can be inherited 3.31 understand that many mutations are harmful but some are neutral and a few are beneficial Mutation - a rare, random change in the genetic code of a gene. The mutated gene will produce a slightly different protein to the original non-mutant gene. The new protein might; A) Work just as well as it did before (neutral mutation) B) Work better than before (beneficial mutation) C) Work worse / not at all (harmful mutation) Beneficial mutations give a selective advantage to the individual. Individuals with this kind of mutated allele are more likely to survive, reproduce and pass their alleles on. This is the basis of: Natural Selection
  54. 54. Evolution by Natural Selection 3.30 describe the process of evolution by means of natural selection Evolution is the process by which the range of organisms on Earth change New species arise through a process known as NATURAL SELECTION 1) Living organisms produce more offspring than are needed to replace them, not all of these off-spring grow up and breed themselves. These offspring have different alleles. 2) Those organisms best suited to their local environment survive best and breed, passing on their genetic (genes/DNA) information to the next generation 3) In this way the different forms will become more and more different until eventually they are a new species
  55. 55. WHAT IS THE SELECTION METHOD 3.30 describe the process of evolution by means of natural selection HOW TO BE SUCCESSFUL IN PASSING ON YOUR GENES (A HOW TO 5 STEP GUIDE): 1) BE ATTRACTIVE (physical and social traits can make you more successful with the opposite sex) 2) REPRODUCE OFTEN (The more offspring you make the better) 3) DON’T WASTE YOUR RESOURCES (Invest only the minimal amount of resources in offspring to see them through to reproduction) 4) HAVE A ‘DEEP’ GENE POOL (The more variable your offspring the better chance of some of them surviving unexpected catastrophes. A little bit of mutation/lots of alleles is not a bad thing) 5) STAY ALIVE!! (Live long enough to reproduce………....then die.)
  56. 56. DARWIN SAID IT BEST 3.30 describe the process of evolution by means of natural selection Darwin came up with this theory 1) Darwin’s 1st Observation: Not all individuals survive 2) Darwin’s 2nd Observation: There is variation in a species 3) Darwin’s Conclusion: The better adapted individuals survive (the “fittest”) and reproduce, passing their alleles onto the next generation. Over time this process leads to evolution. www.darwinawards.com/
  57. 57. THE SUPERBUGS 3.32 understand that resistance to antibiotics can increase in bacterial populations, and appreciate how such an increase can lead to infections being difficult to control 1) Bacteria reproduce very frequently so mutations (different alleles) are common. 2) These mutations can mean that they are no longer affected/controlled by a certain antibiotic 3) Surviving generations carry the mutation (allele)making it easier for them to survive. 4) If bacteria evolve over many generations to be resistant to drugs we are treating them with then they are difficult to control 5) Sometimes they can be controlled using a different antibiotic 6) These bacteria in turn become resistant to new antibiotics due to the high rate or reproduction and random mutations 7) Currently some are becoming resistant to all current know antibiotics. Methicillin-resistant Staphylococcus aureus (MRSA or golden staph), vancomycin-resistant Enterococcus (VRE) and multi-drug-resistant Mycobacterium tuberculosis (MDR-TB) ✔
  58. 58. The Makings of a Mutant (TA) 3.33 understand that the incidence of mutations can be increased by exposure to ionising radiation (for example gamma rays, X-rays and ultraviolet rays) and some chemical mutagens (for example chemicals in tobacco).(TA) Mutations are: a) inherited b) happen on their own (although this is rare). The frequency that mutation occurs naturally can be increased by exposure to radiation • gamma rays • X-rays • ultraviolet rays And Chemical mutagens • chemicals in tobacco..Not Nicotine!)

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