1. Beyond Mendelian Genetics
Incomplete Dominance, Codominance, Multiple Alleles, & Polygenic Traits

2. Beyond Dominant & Recessive
What will happen if some alleles are neither dominant nor recessive?
What will happen if some traits are controlled by more than one gene?

3. Beyond Dominant & Recessive
incomplete dominance – one allele is not completely dominant over the other
e.g., white flower crosses with a red flower = pink flower
codominance – both alleles contribute to the phenotype
e.g., red cow crosses with a white cow = roan cow
multiple alleles – > 2 alleles control the phenotype
e.g., coat color of rabbits
polygenic traits – several genes control the trait
e.g., skin color in humans

4. Types of Dominance

5. Incomplete Dominance

6. Incomplete Dominance neither allele is dominant or recessive
organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parents; an intermediate phenotype is shown

7. Incomplete Dominance R R Rr r r
e.g., cross a red flower (RR) with a white flower (rr) & the offspring will be pink (Rr)!
genotype(s) of offspring: Rr
genotypic ratio:
4:0
phenotype(s) of offspring:
pink
phenotypic ratio: R R Rr
pink r r

8. Incomplete Dominance
when dealing with incomplete dominance, doesn’t matter what letter you use, as long as heterozygous condition always denotes the intermediate trait.
below R is used, but could also use W or P. Ww = pink, Pp = pink if these letters are used

9. Incomplete Dominance R r RR Rr rr R r
e.g., in another flower, if red (Rr) & blue (rr) flowers are crossed, they produce a 3rd purple (Rr) flower
what would be the genotypic ratio and phenotypic ratio if you crossed two purple flowers?
genotype(s) of offspring:
RR, Rr, rr
genotypic ratio:
1:2:1
phenotype(s) of offspring:
red, purple, blue
phenotypic ratio: R r RR
red Rr
purple rr
blue R r

10. CoDominance

11. CoDominance: neither allele is really dominant or recessive
some equally dominant
parents with different phenotypes produce an offspring with a 3rd phenotype
3rd phenotype will show both parental phenotypes simultaneously (at same time)

12. CoDominance:
e.g., in cattle & horses, if you cross a pure red (RR) with a pure white (WW), you get (RW) which produces a 3rd phenotype, a roan color
these cattle or horses actually have both red & white hairs intermixed, or are spotted R R RW
roan W W

13. CoDominance:
What will the offspring be like if you cross a roan colored horse with a white colored horse (RW X WW)?
genotypes?
genotypic ratio?
phenotypes?
phenotypic ratio? R W W W

14. CoDominance: R W RW roan WW white W W
What will the offspring be like if you cross a roan colored horse with a white colored horse (RW X WW)?
genotypes: RW, WW
genotypic ratio:
2:2 or simplified to 1:1
phenotypes: roan, white
phenotypic ratio? R W RW
roan WW
white W W

15. Which are these Examples of?+ = = +

16. Multiple Alleles
2 or more possible alleles for the same gene within a population
however, individuals within the population are only able to hold two of them
an individual can not have more than 2 alleles for a trait, but there are more than 2 allele possible for that trait in the population
non-human examples: rabbit fur color, mice skin color, eye color in flies, wing size in flies

17. Multiple Alleles e.g., blood type - single gene, but 4 phenotypes
Blood Types in Humans
AA or Ao  Type A
BB or Bo  Type B
AB (codominant)  Type AB
oo (recessive)  Type O

18. Polygenic Traits show a wide range of phenotypes
many traits are produced by interaction of several genes
traits controlled by 2 or more genes (1 gene has 2 alleles)
show a wide range of phenotypes
phenotype is produced by the
interaction of more than 1 pair
of alleles
e.g., in humans…
eye color, skin color, & height

19. Examples of Polygenic Traits

20. Examples of Polygenic Traits

22. Examples of Polygenic Traits