1. Blood Types and Sex-linkage

2. Human Blood Types
Human Blood Types have a gene that displays multiple alleles and codominance
The gene has three alleles:
A codes for an A antigen (protein) on red blood cells
B codes for a B antigen (protein) on red blood cells
O codes for no antigen on red blood cells

3. The A and B alleles are codominant
O allele is recessive

4. Blood Type Phenotypes and Genotypes
Phenotypes Genotypes
Type A blood AA or AO
Type B blood BB or BO
Type AB blood AB
Type O blood OO

5. Blood Type Antigens

6. Sex-linked Genes Sex-linkage
Gene for trait is found on a sex chromosome
Most (almost all) are found on the X chromosome; there are very few Y-linked disorders
Can be sex-linked dominant or sex-linked recessive

7. Inheritance of X-linked recessive disorder

8. Inheritance of X-linked recessive disorder

9. X-linked Genotypes and Phenotypes
Genotypes of each parent are written as superscripts on their sex chromosomes
Ex: H=“healthy” allele; h= hemophilia allele
XHXh female carrier of hemophilia
XHXH female w/o hemophilia
XhXh female with hemophilia
XHY male w/o hemophilia
XhY male with hemophilia

10. Sex-linked Punnett Squares
DO NOT CROSS TWO FEMALES
Females are XX, males XY

11. Hemophilia Punnett Square
Hemophilia is x-linked recessive

12. Color blindness (X-linked recessive)

13. X-linked Recessive Disorders
Show up more in males
Females have two X chromosomes
rare to inherit two “bad” X’s to show disorder
One “good” X masks the “bad” X; healthy dominant allele masks the recessive allele
Male have only one X chromosome
Males only need one recessive allele to show the trait b/c they don’t have another X which could carry a healthy dominant allele to mask the recessive allele.