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4.3 theoretical genetics
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4.3 theoretical genetics 4.3 theoretical genetics Presentation Transcript

  • Genetics 4.3 Theoretical Genetics
  • Definitions
    • Genotype: The alleles of an organism.
    • Phenotype: The characteristics of an organism.
    • Dominant allele: an allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state. E.g. Bb and BB give brown hair.
    • Recessive allele: An allele that only has an effect on the phenotype when present in the homozygous state. E.g. bb gives you blond hair.
    • Codominant alleles: Pairs of alleles that both affect the phenotype when present in a heterozygote. E.g. C R C W gives a pink flower because both red and white genes are codominant.
    • Locus: The particular position on homologous chromosomes of a gene.
    • Homozygous: Having two identical alleles of a gene.
    • Heterozygous: Having two different alleles of a gene.
    • Carrier: An individual that has only one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for the allele.
    • Test cross: Testing a suspected heterozygote by crossing it with a known homozygous recessive.
  • Punnet Square
  • A monohybrid cross
    • Cross a smooth and wrinkled seed together. Then cross the offspring with each other:
  • Performing crosses
    • 1. A heterozygous tall pea plant is crossed with a homozygous short pea plant. What are the F 1 offspring?
  • Performing crosses
    • 1. A heterozygous tall pea plant is crossed with a homozygous short pea plant. What are the F 1 offspring?
    • P 1 Tt x tt
    T t t
  • Performing crosses
    • 1. A heterozygous tall pea plant is crossed with a homozygous short pea plant. What are the F 1 offspring?
    • P 1 Tt x tt
    T t t t t t T
  • Performing crosses
    • 1. A heterozygous tall pea plant is crossed with a homozygous short pea plant. What are the F 1 offspring?
    • P 1 Tt x tt
    T t t t t t T Tt Tt Tt tt
  • Performing crosses
    • 1. A heterozygous tall pea plant is crossed with a homozygous short pea plant. What are the F 1 offspring?
    • P 1 Tt x tt
    T t t t t t T F 1 Results: ½ Tt – Tall pea plants ½ tt – short pea plants Tt Tt Tt tt
  • Multiple Alleles
    • Some genes have more than two alleles.
    • E.g. Human blood types.
    • Type A = I A I A or I A i
    • Type B = I B or I B i
    • Type AB = I A I B
    • Type O = ii
  • ABO blood groups
    • An example of multiple alleles and codominance.
    • The blood type AB is codominant because both A and B are expressed phenotypically.
  • Performing crosses
    • 2. A man with type AB blood and a woman with type O blood have a child. What is the probability that this child will be type A?
  • Performing crosses
    • 2. A man with type AB blood and a woman with type O blood have a child. What is the probability that this child will be type A?
    • P 1 I A I B x ii
    I A I B i
  • Performing crosses
    • 2. A man with type AB blood and a woman with type O blood have a child. What is the probability that this child will be type A?
    • P 1 I A I B x ii
    I A I B i I B i i I A
  • Performing crosses
    • 2. A man with type AB blood and a woman with type O blood have a child. What is the probability that this child will be type A?
    • P 1 I A I B x ii
    I A I B i I B i i I A I A i I A i I B i I B i
  • Performing crosses
    • 2. A man with type AB blood and a woman with type O blood have a child. What is the probability that this child will be type A?
    • P 1 I A I B x ii
    I A I B i I B i i I A F 1 Results: ½ I A i – type A blood ½ I B i – type B blood The probability of type A is 50% or 1:2 I A i I A i I B i I B i
  • Sex Chromosomes
    • The X and Y chromosomes control gender.
    • Females have XX while males have XY.
  • Sex Linkage
    • Sex linked genes are found on the sex chromosomes. They are usually on the X.
    • Colour blindness and hemophilia are two examples of sex linked genetics.
  • Colourblindness
    • X B = normal vision
    • X b = colourblindness
    • X B X B = normal female
    • X B X b = female carrier
    • X b X b = colourblind female
    • X B Y = normal male
    • X b Y = colourblind male
  • Hemophilia
    • X H = normal blood clotting
    • X h = hemophilia
    • X H X H = normal female
    • X H X h = female carrier
    • X h X h = hemophiliac female
    • X H Y = normal male
    • X h Y = hemophiliac male
  • Performing crosses
    • 3. A man with colourblindness and a woman who is a carrier have a male child. What is the probability that this child will be colourblind?
  • Performing crosses
    • 3. A man with colourblindness and a woman who is a carrier have a male child. What is the probability that this child will be colourblind?
    • P 1 X b Y x X B X b
    X b Y X B X b
  • Performing crosses
    • 3. A man with colourblindness and a woman who is a carrier have a male child. What is the probability that this child will be colourblind?
    • P 1 X b Y x X B X b
    X b Y X B X b X b Y X B X b
  • Performing crosses
    • 3. A man with colourblindness and a woman who is a carrier have a male child. What is the probability that this child will be colourblind?
    • P 1 X b Y x X B X b
    X b Y X B X b X b Y X B X b X B X b X b X b X B Y X b Y
  • Performing crosses
    • 3. A man with colourblindness and a woman who is a carrier have a male child. What is the probability that this child will be colourblind?
    • P 1 X b Y x X B X b
    X b Y X B F 1 Results: ¼ X B X b – carrier normal female ¼ X b X b – colourblind female ¼ X B Y – normal male ¼ X b Y – colourblind male The probability of colourblindness in the male child is 50% or 1:2 X b X b Y X B X b X B X b X b X b X B Y X b Y
  • Pedigree Charts
  • A Sample Pedigree
  •  
  •