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.