Complex Patterns of Inheritance

Complex Patterns of

Inheritance

2

Patterns of Inheritance

So far we have learned that the presence of one dominant allele produces a

dominant phenotype. However, not all allele pairs have a dominant-recessive interaction

There are FOUR other patterns of inheritance that we will learn about!

●Incomplete Dominance

●Codominance

●Multiple Alleles

●Polygenic Inheritance

INCOMPLETE DOMINANCE

●Traits appear to be a combination (mixture) of alleles

●Offspring’s phenotype is a combination of the parents’ phenotypes

●Ex: camellia plant

●IN HUMANS: straight/curly/wavy hair

CODOMINANCE

●

BOTH alleles from the parents can be observed in the offspring’s phenotype

●

Ex: cattle fur

●IN HUMANS: AB blood type

3 phenotypes indicates incomplete/co-dominant inheritance

MULTIPLE ALLELES

●

Some traits have more than just *two* alleles

●

IN HUMANS: blood type has 3 possible alleles
○Certain alleles for blood type are codominant but also are dominant to the other allele

POLYGENIC INHERITANCE

●It was originally believed that traits were decided by ONE gene

●We now know that some traits can be affected by more than one gene!

●Polygenic inheritance occurs when multiple genes determine the phenotype of a trait

●IN HUMANS: eye color, height, weight, and skin color

B=Brown
b=Blue
G=Green
g=Hazel
R=Black
r=Gray

4 or more phenotypes indicate multiple allele/polygenic inheritance

FUN FACT!

● Certain genes in your body turn on and off at different times

during your life.

● For instance, the genes that control hair color turn off in most

people when they get older, thus causing hair to turn gray or white.

● Some babies are born with all of the genes for eye color not

turned "on" yet, so their eye color might change in the first few months.

VIDEO: Incomplete Dominance, Codominance, Polygenic Traits, & Epistasis