Intermediate Inheritance & Sex-linked Inheritance

What is Intermediate Inheritance? The heterozygous hybrid (Hh) offspring have a trait that is not exactly like the trait of either homozygous purebred (HH) or (hh) parent.

Three forms of Intermediate Inheritance 1. Co Dominance- ex. Human blood type 2. Incomplete Dominance- Ex. Color of animal fur or flower 3. Polygenic - Ex. Human eye color

Co Dominance Both alleles in the heterozygous form express themselves fully They are equally emphasized or strong. Example: Blood Types

Human Blood Types Red Blood cells are responsible for transport of oxygen and carbon dioxide Red blood cells are coated with different proteins named “A” or “B If the red blood cells have no protein coat at all. We call this “O”

“A” , “B” & “O” Blood Type Type “A” is the dominant trait Type “B” is the dominant trait Type “O” blood has no protein and must be inherited by both parents as a recessive trait AA AO BB BO OO

AB “AB” Blood Type Type AB “A” protein and “B” protein are equally expressed on one blood cell. This is an example of co-dominance Neither protein is dominant over the other. AB

Incomplete Dominance There are two different alleles for the same trait but neither is completely dominant over the other. The phenotype of the heterozygous offspring is a mix between the two parents. The alleles continue to be carried separately and are transmitted to the next generation as their original phenotype.

Example of Incomplete Dominance Neither red flowers (rr) nor white Flowers (ww) are completely dominant traits. When crossed all offspring will be pink (rw) which is a mixture of the two traits.

Polygenic Traits Traits that are affected by 2 or more pairs of alleles. Alleles may be scattered along one chromosome or located on several chromosomes.

Example of Polygenic Trait Human eye color Pigment color- chromosome 19 Amount of pigment (brown or green) - chromosome 15

Multiple alleles for the same trait An individual only has two alleles for each trait. But some traits have more than 2 alleles present in a population. There are more possibilities of outcome due to the combination of these different alleles. Coat color in rabbits is inherited as a series of multiple alleles.

Sex-Linked Inheritance Sex-linked traits are controlled by genes found on the X chromosome but NOT on the Y chromosome. Females = XX – carry 2 alleles for a sex-linked trait Males = XY – only carry 1 allele for a sex-linked trait, so it is more likely for them to get sex-linked traits or diseases

Sex-Linked Traits, cont. Males (XY) receive sex-linked traits from their mother because their mother gives them the X chromosome and their father gives them the Y chromosome.

Example: Colorblindness Colorblindness is a condition that affects a person's perception of colors. This leads to changes in color vision, that range from mild difficulty in recognizing shades, to total inability of detecting colors.

Are you colorblind?

Inheritance of Colorblindness N = Normal color perception (not colorblind) n = Colorblind Normal male: Male with colorblindness: Normal female (not a carrier for colorblindness – homozygous): Normal female (carrier for colorblindness – heterozygous): Female with colorblindness: XNY XnY XNXN XNXn XnXn

Sample Problem

XNXn x XNY XN XNXN XNXn Y XNY XnY Chances of: a. colorblind son? _______ b. colorblind daughter? ________ c. daughter who is a carrier? _____ d. child who is not colorblind? ________ XN Xn 1/2 or 50% XN Y XNXN XNXn 0/2 or 0% XNY XnY 1/2 or 50% 3/4 or 75%