Chapter 11.3

Other Patterns of Inheritance

Four exceptions to Mendel’s principles

In most organisms, heredity is more complicated than Mendel realized

1Incomplete Dominance

2Co-

dominance

3Multiple Alleles

4Polygenic Traits

Incomplete Dominance-

Some alleles are neither dominant NOR recessive!!

1

Heterozygous type lies somewhere between the 2 homozygous types-IT’s A BLEND

For Example:

Four O’Clock Flowers

Incomplete dominance Continued

Inco

mpl

ete

Dom

inan

ce C

on’t Heterozygous type lies somewhere between the

2 homozygous types- A BLEND!!

Red + White = Pink

2 Co-dominance

Phenotypes produced by both alleles are clearly expressed

NOT BLENDED! TRAITS STAY DISTINCT AND UNIQUE

BOTH TRAITS EQUALLY STRONG

In some chickens, the gene for feather color is controlled by co-dominance. The allele for black is B and the allele for white is W. The heterozygous, BW, phenotype is known as erminette, or speckled.

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Erminette chickens- examples of CODOMINANCE- both traits show up distinctly

Ie: In humans, gene for protein that controls cholesterol levels in the blood Ie: Roan cows- A white cow and red bull makes red and white spotted offspring, also known as "roan”.

Other examples of Co-dominance

"What is the difference between co-dominance and incomplete dominance?"Co-dominance happens when there are two dominant alleles for a trait and they are both shown.

For example, a red and white flower would make a striped flower. A white cow and brown cow makes a brown and white spotted cow, also known as "roan”.

Incomplete dominance happens when there are two dominant alleles for a trait and they are blended (mixed).

For example, a red flower and a white flower would make a pink flower.

3 Multiple Alleles

Many genes exist in several different forms, so they are said to have multiple alleles.

For example: coat color in rabbits, there is ONE gene with at least FOUR different alleles

Multiple Alleles Continued

Another Example:Human blood type

Multiple Alleles Continued

POLYGENIC TRAITS

Traits controlled by 2 or more genes

Many traits are produced by interaction of several genes

• For example: at least 3 genes control reddish-brown pigment in eyes of fruit flies

Many traits are produced by interaction of several genes

• For example: more than 4 genes control skin color in humans

Many traits are produced by interaction of several genes

• More examples of Polygenic traits: Hair and eye color in humans

• http://www.allaboutvision.com/conditions/eye-color-chart.htm

Environmental conditions (internal or external) can affect gene expression

Genes and the Environment

Temperature affecting butterfly color

Pontia occidentalist, from western North America is light in color when emerges in the summer, and darker in color when it emerges in the spring p.321

Internal environment & genes

Genes and the environment: another example… gene for male pattern baldness is found in both males and females, but the male hormones TRIGGER it.

Review: Four exceptions to Mendel’s principles

In most organisms, heredity is more complicated than Mendel realized

1Incomplete Dominance

2Co-

dominance

3Multiple Alleles

4Polygenic Traits

What’s Your Message?Other patterns of inheritance