Patterns Beyond Simple Dominance
When inheritance is more complex
Incomplete dominance
In incomplete dominance, the heterozygous phenotype is intermediate between the two homozygous phenotypes. For example, red and white flowers may produce pink flowers.
Codominance
In codominance, both alleles are fully expressed in the phenotype. A classic example is blood type .
Polygenic traits
Some traits are influenced by many genes at once. These are called polygenic traits. Height, skin color, and body weight are examples of traits influenced by many genes and the environment.
Simple rules are useful, but limited
Dominant and recessive inheritance is only one pattern among many. Real biology often involves multiple genes and interactions.
Three inheritance patterns
Incomplete dominance
- Heterozygote is intermediate
- Example: pink flowers from red and white parents
Codominance
- Both alleles are expressed
- Example: blood type
Which example is often used for codominance?
In blood type AB, both and alleles are expressed.
Correct answer: Blood type AB
What is a polygenic trait?
Polygenic means multiple genes contribute to the phenotype.
Correct answer: A trait influenced by many genes
In incomplete dominance, the heterozygous phenotype is usually:
The heterozygote often shows a blended or intermediate phenotype.
Correct answer: Intermediate