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Genetics Part 2

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  • 1. Advanced Genetics McCammon Biology I
  • 2. Mendelian Genetics
    • These are the types of problems we had before Christmas.
    • Monohybrid crosses
    • Dihybrid crosses
    • Test cross
  • 3. Incomplete Dominance
    • This is a condition in which NEITHER allele for a particular trait is dominant over the other.
    • For example: red-flowered snapdragons crossed with white ones yield pink.
  • 4. Incomplete Dominance
    • For these problems, you should make a key for each problem in addition to the Punnett Square, genotype, and phenotype.
    • RR = Red (One of the two traits)
    • R’R’ or WW = White (The other trait)
    • RR’ or RW = Pink (Blending of the two traits)
  • 5. ABO Blood Types: A Case of Codominance
    • In codominance, both alleles are expressed in heterozygotes.
    • In codominance, instead of NEITHER allele being dominant, BOTH alleles are dominant.
  • 6. ABO Blood Types: A Case of Codominance
    • For these problems, you should also make a key for each problem in addition to the Punnett Square, genotype, and phenotype.
    • F B F B = Black Feathers (One Trait)
    • F W F W = White Feathers (The other Trait)
    • F B F W = Black and White Speckled Feathers (Heterozygous = spotted)
  • 7. ABO Blood Types: A Case of Codominance
    • Blood type is determined by markers produced by three genes – This is called multiple alleles.
      • I A and I B are each dominant to i, but are codominant to each other.
      • Therefore, some persons can express I A and I B and have AB Blood Type.
  • 8.
    • The four blood types are
    • A = I A I A or I A i
    • B = I B I B or I B i
    • AB = I A I B only
    • 0 = ii only
    ABO Blood Types: A Case of Codominance
  • 9. Autosomes and Sex Chromosomes
    • There are 44 autosomes (22 pairs) and 2 sex chromosomes (1 pair)
  • 10. Autosomes and Sex Chromosomes
    • Gender is determined by sex chromosomes
      • Human females have two X chromosomes
      • Human males have one X chromosome and one Y chromosome.
      • All normal human eggs carry only one X chromosome
      • Half of the sperm carry an X chromosome and the other half carry a Y chromosome.
  • 11. Autosomes and Sex Chromosomes
    • Sex determination in humans
      • If an X bearing sperm fertilizes an X bearing egg, a female results.
      • If a Y bearing sperm fertilizes an X bearing egg, a male results.
        • XX – female
        • XY - male
  • 12. Sex-Linked Traits
    • Some genes are only found on sex chromosomes.
      • Genes for color blindness; gene for male pattern baldness; gene for hemophilia.
  • 13. Sex-Linked Traits
    • Here are the genotypes and you will need to know:
    • X B X B = Normal female
    • X B Y = Normal Male
    • X B X b = Normal female (but she’s a carrier)
    • X b X b = Affected female
    • X b Y = Affected male
    • Y will not have a letter.
  • 14. Pedigrees
    • A pedigree is a diagram that shows the history of trait.
    • Where Punnett’s squares predict the future, pedigrees map the past.
  • 15. Pedigrees
    • It is used by geneticists to determine if a trait is sex-liked.
      • Squares represent males
      • Circles represent females
      • A horizontal line represents a mating
      • A vertical line represents children
      • If the circle or square is shaded in, this means they are affected
  • 16. Pedigrees
      • A triangle means abortion or miscarriage
      • A diamond indicates a person of unknown sex
      • A diagonal line through a circle or square means the person is dead.
      • A diagonal line through a mating means divorce or the pair is not together anymore.
      • The children are listed in birth order.
      • Each generation is marked with roman numerals
      • Each individual is marked with a number starting at the top left.