1. Incomplete Dominance, Codominance, Multiple Alleles, and Sex-Linked Genes

2. Incomplete dominance This is when neither allele is dominant.
Both alleles are expressed and contribute equally to the phenotype.
A heterozygous genotype has an intermediate phenotype as there is partial influence from both alleles.
Example: Red + White = Pink
flower flower flower

3. Incomplete dominance Snapdragons can be
red (alleles = RR)
white (alleles = rr)
pink (alleles = Rr)
If you cross a two pink flowers, is it possible to produce a white flower?
¼ Red
¼ White
½ Pink
Yes!

4. Codominance Both alleles are dominant.
They are independent, so there is no 'blending' as in the snapdragons, instead the phenotype is a result of the full expression of both alleles.
Example: black + White = B&W spotted
dog dog dog

5. Codominance Dogs can be Black (alleles = BB) White (alleles = bb)
Spotted (alleles = Bb)
Is it possible for a black dog to have one parent that is white?
No!

6. Multiple alleles (blood typing)
In the case of the ABO blood grouping, there are 3 alleles for one gene
They are written a little differently:
i : this allele is recessive
IA : this allele is co-dominant
IB : this allele is co-dominant

7. Multiple alleles (blood typing)
Blood group (phenotype):
A ……………………………..
B ……………………………..
AB ……………………………
O ……………………………..
Possible genotype:
IA IA or IAi
IBIB or IBi
IAIB ii

8. Multiple alleles (blood typing)
A father with homozygous type A blood has a child with a mother that has heterozygous type B blood.
Is it possible for them to have a child with type O blood?

9. Sex determination
Gender is determined by sex chromosomes in many animals.
The XY System:
Female are XX, males are XY
Y makes the guy!!!
What are the odds that a couple have a boy?
50/50

10. Sex-linked genes
Some genes are linked to the sex chromosomes and are inherited with them.
Hemophilia is carried on the X chromosome.
The normal allele is dominant (H)
The allele for hemophilia is recessive (h)

11. Sex-linked genes XHXH = normal female XHXh = carrier female
XhXh = female w/hemophilia
XHY = normal male
XhY = male w/hemophilia
A carrier does not have the disease, but can pass it on to their offspring.

12. Sex-linked genes
If a female carrier has offspring with a normal male, what is the chances that their offspring will have hemophilia?
25%

13. Sex-linked genes
In cats the allele for coat color is carried on the X chromosome.
The alleles are black and orange but they are codominant.
XBXB = black female
XBY = black male
XbXb = orange female
XbY = orange male
XBXb = tortoiseshell female

14. Sex-linked genes
Can an orange male and a black female produce a tortoiseshell male?
No!

15. Sex-linked genes
What is the genotype of the father?

16. Sex-linked genes Mother can provide XB or XO
Father can provide Y plus 1 other allele.
Since 1 offspring is XO XO, the father must provide 1 of these allele.
Therefore, the father's genotype is XOY