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Polygenetic Inheritance

Polygenetic Inheritance. Skin color. Melanin, its only skin deep…. Differences in skin color are largely due to the amounts of melanin. A dark pigment produced by skin cells. At least 3 genes control synthesis of melanin. Each one has two forms: An allele for high melanin production

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Polygenetic Inheritance

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  1. Polygenetic Inheritance Skin color

  2. Melanin, its only skin deep… • Differences in skin color are largely due to the amounts of melanin. • A dark pigment produced by skin cells. • At least 3 genes control synthesis of melanin. • Each one has two forms: • An allele for high melanin production • Dark skin (ABC) • And allele for low melanin production • Light skin (abc)

  3. Each dark skin allelle (ABC) in the genotype adds a small but equal amount of pigment. • There are 7 different shades of skin color, ranging from very dark (AABBCC) to very light (aabbcc). • Most individuals produce medium amounts of melanin and are intermediate skin color (AaBbCc)

  4. Punnett Square • How many possible shade of skin color? • 7, AaBbCc x AaBbCc • The offspring of this cross exhibit seven shades of skin color based on the number of dark-skin alleles in each genotype. • How many genes regulate melanin production? • 3 • How many forms of the gene are present? • 2, dark-allele & light-skin allele • Complete the table to determine the number of offspring with each skin color. • How many of these 64 possible offspring have skin darker than their parents? • 3 genes has two alleles. Are the dark-skin alleles dominant to the light-skin alleles? • no • What environmental factors would influence gene expressions?? • Sunlight, nutrition

  5. What would an individual with the aabbcc genotype look like? • A very fair haired, pale skinned individual, like Northern Europeans.

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