Why are only female cats calico?  This is when both genes are dominant, so the presence of both alleles you will see they are both fully expressed. IAIA or IAi= A type IAIB = AB type IBIB or IBi = B type ii = O type  Neither of the genes is dominant to the other, so the heterozygous genotype creates a 3rd phenotype.  The two phenotypes are blended.

Roan Horse  Which is an example of incomplete dominance and which is an example of codominance?

 Most traits in humans are not controlled by only 1 gene. There are many genes that contribute to a single trait.

Eye color

Hair color • A modifier gene controls another gene. • Not dominant, because it is not on the same gene, but will still override whatever gene it is the modifier for.

Heterochromia iridum

Eye color is an example of a polygenic trait and Albinism is an example of a blocked trait.  How is eye color determined?

 How is whether or not an organism will be albino determined?  Some traits are carried on the sex chromosomes. Women have XX and men have XY.  If a trait is carried on the X chromosome then women have two of them and men only have one.

hemophilia Muscular dystrophy An example of this is color blindness Ex: Red/green color blindness is a recessive trait carried on the X chromosome.

 Men can have either XBY or XbY

 If he has XBY he is not color blind (the big B stands for the dominant trait of not color blind)

 If he has XbY he is colorblind.

 Because this trait is not carried on the Y chromosome there is no opportunity to be heterozygous for males. Women can have XBXB, XBXb, or XbXb

If she has XBXB, she is not color blind

If she has XBXb, she is not color blind (the B is dominant to the b so this woman is a just a carrier of the trait)

If she has XbXb, then she is colorblind. A woman has the genotype XbXb and a man has the genotype XbY .  Are either of them colorblind? Yes both because they each have the recessive alleles (b) for them.  If these two individuals had children what is the likelihood that their children would be colorblind? 100% This is why there are many more males that are color blind than females.

Calico coloration

Male Pattern Baldness