1. Non-Mendelian Genetics

2. Mendelian Genetics: Dominant & Recessive Review
One allele is DOMINANT over the other (because the dominant allele can “mask” the recessive allele)
genotype: PP
genotype: pp
genotype: Pp
phenotype: purple
phenotype: white
phenotype: purple

3. Review Problem: Dominant & Recessive
In pea plants, purple flowers (P) are dominant over white flowers (p). Show the cross between two heterozygous plants.
P p
GENOTYPES:
- PP (25%) Pp (50%)
pp (25%)
- ratio 1:2:1 P p PP Pp Pp pp
PHENOTYPES:
- purple (75%) white (25%)
- ratio 3:1

4. Non-Mendelian Genetics
Incomplete Dominance
Codominance
Multiple Alleles
Polygenic Traits
Sex-Linked Traits

5. Incomplete Dominance
a third (new) phenotype appears in the heterozygous condition as a BLEND of the dominant and recessive phenotypes. Ex - Dominant Red (R) + Recessive White (r) = Hybrid Pink (Rr)
RR = red
rr = white
Rr = pink

6. Codominance Example: Speckled Chickens
BB = black feathers
WW = white feathers
BW = black & white speckled feathers
Notice –
NO GRAY!
NO BLEND!
Each feather is
either black or white

7. Codominance Example: Rhodedendron
R = allele for red flowers
W = allele for white flowers
Cross a homozygous red flower with a homozygous white flower.

8. Codominance Example: Roan cattle
cattle can be red (RR – all red hairs) white (WW – all white hairs) roan (RW – red and white hairs together)

9. Codominance Example: Appaloosa horses
Gray horses (GG) are codominant to white horses (WW). The heterozygous horse (GW) is an Appaloosa (a white horse with gray spots).
Cross a white horse with an appaloosa horse.
W W G W GW GW WW WW

10. Polygenic Traits
traits produced by multiple genes
example: skin color

11. Sex-Linked Traits
Gene is attached to the X chromosome only, not found on the Y chromosome at all. (women have XX, men have XY chromosomes). These disorders are more common in boys.
examples: red-green colorblindness

12. Sex-Linked Traits
in males, there is no second X chromosome to “mask” a recessive gene. If they get an X with the disorder, they have it. Girls must inherit defective X’s from both parents.

14. Sex-Linked Traits A: 29, B: 45, C: --, D: 26  Normal vision
 Red-green color blind
A: 70, B: --, C: 5, D: 6
 Red color blind
A: 70, B: --, C: 5, D: 2
 Green color blind