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Polygenic Inheritance

Polygenic Inheritance. Trait controlled by 2 or more genes May be on the same or different chromosomes Shows a range , intermediate is most common phenotype Upper and lower case letters used. Many variations in skin color. Skin color: A polygenic trait.

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Polygenic Inheritance

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  1. Polygenic Inheritance • Trait controlled by 2 or more genes • May be on the same or different chromosomes • Shows a range, intermediate is most common phenotype • Upper and lower case letters used

  2. Many variations in skin color

  3. Skin color: A polygenic trait Determining # of Genes Involved in Skin Color Expected distribution- 4 genes Observed distribution of skin color Expected distribution- 1 gene Number of individuals Expected distribution- 3 genes Light Right Range of skin color

  4. Skin Color • Skin color is actually due to 5 genes • Genotypes darkest to lightest: • AABBCCDDEE would be darkest • AaBbCcDdEe would be medium • aabbccddee would be lightest

  5. Influence of external environment • In arctic foxes temperature has an effect on the expression of coat color. In winter, fur is white.

  6. Arctic Fox in summer coloration: influence of external environment

  7. Influence of external environment External influences can also be seen in leaves. Leaves can have different sizes, thicknesses, and shapes depending on the amount of light they receive.

  8. Influence of internal environment The internal environments of males and females are different because of hormones and structural differences. An organism’s age can also affect gene function.

  9. Peacock (male) Peahen (female)

  10. Sex-linked Traits • Traits (genes) located on thesex chromosomes • Sex chromosomes are X and Y • XX genotype for females • XY genotype for males • Many sex-linked traits carried on X chromosome

  11. fruit fly eye color XX chromosome - female Xy chromosome - male Sex-linked Traits Example: Eye color in fruit flies Sex Chromosomes

  12. Xr Xr XR Y Sex-linked Trait Problem • Example: Eye color in fruit flies (red-eyed male) x (white-eyed female)XRY x XrXr Remember: the Y chromosome in males does not carry traits. RR = red eyed Rr = red eyed rr = white eyed XY = male XX = female

  13. Xr Xr XR Xr XR Xr XR Y Xr Y Xr Y Sex-linked Trait Solution: 50% red eyed female 50% white eyed male

  14. Female Carriers • Females are carriers of sex-linked traits if they have the heterozygous genotype. • Males cannot be carriers because they only have one X chromosome. • Female parents who are carriers, pass sex-linked traits to all children, but males are usually the ones who express the trait.

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