Complex Pattern Of Inheritance

Multiple Alleles

Traits are controlled by more than two alleles that usually code for a certain characteristic in a species.

There are two possible phenotype's.

The human ABO blood type is a good example of multiple alleles. Humans can have red blood cells that are of type A , type B , or type O . These three different alleles can be combined in different ways following Mendel's Laws of Inheritance

Incomplete Dominance

Neither gene is dominant over the other.

So, the offspring in heterozygous will result in a new phenotype

Examples of incomplete dominance are:

A snapdragon flower that is pink as a result of cross-pollination between a red flower and a white flower when neither the white or the red alleles are dominant.

A brown fur coat on a rabbit as a result of one rabbit's red allele and one rabbit's white allele not dominating.

Codominance

Both alleles are expressed.

Offspring that are hetrozygous receive one version of the gene from each parent.

For example

A cow with brown hair and a cow with black hair mate, therefore the offspring has both brown and black hair


If the male has A blood group and the female B blood group then the human offspring might have AB blood group

Polygenic traits

Trait controlled by nonallelic gene.

phenotypes are controlled by multiple genes.

For example
Most polygenetic traits are partially influenced by the environment. For example, height is partially influenced by nutrition in childhood. If a child is genetically programmed to be average height but does not get a proper diet, he or she may be below average in size.