1. Exceptions to Mendelian Inheritance

2. Complete Dominance Mendel investigated complete dominance
dominant gene totally masks the recessive

3. Complete Dominance
Punnett squares are used to predict offspring genotypes and phenotypes.
Hint: Dominant allele wins!!!

4. Incomplete Dominance
A cross between organisms with two different phenotypes can produce offspring with a third phenotype that is a blending of the parental traits. 

5. Incomplete Dominance It's like mixing paints
Red + white will make pink
Red doesn't totally dominate the white, instead there is incomplete dominance, and we end up with something in-between.
Hint: Dominant allele DOES NOT win!!!
There is not even a dominant allele present!

6. Incomplete Dominance

7. Incomplete Dominance
How to recognize a question involving incomplete dominance:
Notice that the offspring show a 3rd phenotype.  Parents each have a phenotype, and the offspring are different from the parents.
Notice that the trait in the offspring looks like it is a blend of the parental traits.
Hint: neither allele wins!!

8. Incomplete Dominance
Can still use the Punnett square to solve problems involving incomplete dominance. 
The letters used to represent each allele will be different, lowercase letters
Why lowercase?
Because neither allele dominates the other
Hint: nobody wins!!

9. r r Incomplete Dominance w w rw rw rw rw P generation:
r = red flowers w = white flowers
Cross red and white flowered plants
rr x ww
F1 Results?
Genotype: 100% rw
4 : 0 ratio
Phenotype: 100% pink r r rw rw w rw rw w
F1 generation

10. Incomplete Dominance

11. r w Incomplete Dominance r w rr rw rw ww F1 self cross:
r = red flowers w = white flowers
Cross pink and pink flowered plants
rw x rw
F2 Results?
Genotype:
25% rr 50% rw 25% ww
1 : 2 : 1 ratio
Phenotype:
25% red 50% pink 25% white r w rr rw r rw ww w
F2 generation

12. Incomplete Dominance

13. Incomplete Dominance: Example
A cross between a blue bird & a white bird produces offspring that are silver. 
What are the genotypes of the parent birds in the cross?
b= blue
w= white
What is/are the genotype(s) of the silver offspring?
What would be the phenotypic percent of offspring produced by two silver birds?
25% blue
25% white
50% silver
bb x ww bw

14. Incomplete Dominance: Example
When two plants with orange fruits are crossed the following phenotypic ratios are present in the offspring:
25% red fruit,
50% orange fruit,
25% yellow fruit. 
What are the genotypes of the parent orange-fruited plants?
ry x ry

15. red x white = red & white spotted
Co-dominance
Prefix "co-" means "together“
Cooperate = work together
Coexist = exist together
The heterozygous organism has a third phenotype in which both of the parental traits appear together. 
Hint: both alleles win!!
red x white = red & white spotted

16. Co-dominance
A very very very very very common phenotype used in questions about co-dominance is roan fur in cattle. 
Cattle can be red, white or roan (red & white hairs together). 
So can horses.

17. Co-dominance Dominance

18. Co-dominance
Can still use the Punnett square to solve problems involving co-dominance. 
The letters used to represent each allele will be different, CAPITAL letters
RR = all red hairs
WW = all white hairs
RW = red & white hairs together.
Hint: both alleles win!!

19. Co-dominance How to recognize a question involving co-dominance:
Notice that the offspring show a 3rd phenotype.  The parents each have one, and the offspring are different from the parents.
Notice that in the offspring BOTH of the parental traits are expressed,
It is NOT a mix or a blend.

20. Co-dominance: Practice
Predict the phenotypic ratios of offspring when a homozygous white cow is crossed with a roan bull.
50% WW - White
50% WR - Roan
What should the genotypes & phenotypes for parent cattle be if a farmer wanted only cattle with red fur?
Both parents should be RR, red
WW x WR

21. Co-dominance: Practice
A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur together).
What pattern of inheritance does this illustrate?
Co-dominance
What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?
0% tan
50 % Tabby
50% Black