complex inheritance

Objectives

Discuss why Mendel’s principles cannot be applied to all situations.

Compare and contrast different types of complex inheritance.

It’s complicated

Mendel got lucky

All of the traits that he studied were only controlled by two alleles

Remember: an allele is a form of one gene (yellow or green)

All of the traits were perfectly dominant or recessive

It’s complicated

Unfortunately, most traits are not so neat and tidy

It’s complicated

There are 4 forms of complex inheritance you need to know

Incomplete dominance

Co-dominance

Multiple Alleles

Polygenic inheritance

Incomplete Dominance

Remember, a gene is the instruction for a protein

Because there are two alleles for a trait, two proteins are being produced

In Mendel’s studies, one protein dominated the other

The dominant protein was shown


Incomplete Dominance: One gene does not clearly dominate the other

The phenotype of the offspring is a blend of the two parent phenotypes


Example: A white flower is mixed with a red flower

In incomplete dominance a white flower mixed with a red flower produces PINK offspring

The offspring are a blend of the two parents

Neither parent is seen in the offspring

Co-dominance

Co-dominance: Neither phenotype dominates and BOTH are shown

Co-dominance

Example: A red flower is mixed with a white flower

In co-dominance a red parent flower and a white parent flower produce offspring with BOTH red AND white petals

Compare

Incomplete dominance:

Red + White = Pink

Co-dominance:

Red + White = Both red and white on the same flower

Multiple Alleles

With all of the variety in the world it would make sense that some traits have more than two forms

Multiple Alleles

Multiple Alleles: A trait for which there are more than 2 forms of a gene

Multiple Alleles

Example: Blood Type

There are three alleles for blood type

IA

IB

i

Multiple Alleles

Genotypes for type A blood are

IA IA or IAi

Genotypes for type B blood are

IB IB or IBi

Genotype for AB blood is

IA IB

Genotype for type O blood is

ii

Polygenic Inheritance

If you have noticed, most kids are a blend of their parents traits

To this point all of the traits we have talked about have been controlled by different forms of ONE gene


Polygenic Inheritence

Remember your words

Poly = many

What do you think POLYgenic inheritance means?


Polygenic inheritance: A trait that is controlled by multiple genes working together

Some good examples

Skin color

Eye color

Height


There are many genes that control skin color, eye color, or height

The interaction of those genes controls the precise color of your skin, color of your eyes, or your height

Business

complex inheritance