Simple Traits
• One gene pair
• Only two alleles
• Genotypes
• Phenotypes
• Examples
Multiple Alleles
• Three or more alleles
• Genotypes & phenotypes
• Human blood type
1. Alleles – A, B, O
2. One gene pair
3. A, B codominant – O recessive
1
Inheritance Problem #1
How many possible genotypes are
there for human blood type?
How many possible phenotypes?
Polygenic Traits
• Definition
• Inherit more than
two alleles/trait
• Parakeet color
1. Two gene pairs
2. Inherit 4 alleles
• Human examples
Inheritance Problem #2
There are three alleles for parakeet
feather color – blue, yellow and white.
Blue and yellow blend to green.
(Incomplete dominance)
White is recessive.
Blue (B)
Yellow (Y)
White (b or y)
2
Inheritance Problem #2
How many possible phenotypes are
there for feather color?
How many possible
genotypes?
Environmental Factors
• Influences outside the cells
• Himalayan rabbit
• Fruit flies
• Plants
Hormones
• Gene expression
• Male-pattern baldness
• Male and female birds
3