1. Intermediate Inheritance & Sex-linked Inheritance

2. 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.

3. 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

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

5. 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”

6. “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

7. 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

8. 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.

9. 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.

10. 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.

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

12. 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.

14. 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

15. 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.

16. 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.

17. Are you colorblind?

20. 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

21. Sample Problem

22. 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%