Download Blood types and sex

Blood Types and
Sex-linkage
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
The A and B alleles are codominant
O allele is recessive
Blood Type Phenotypes and
Genotypes
Phenotypes
Type A blood
Type B blood
Type AB blood
Type O blood
Genotypes
AA or AO
BB or BO
AB
OO
Blood Type Antigens
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
Inheritance of X-linked
recessive disorder
Inheritance of X-linked
recessive disorder
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
Sex-linked Punnett Squares
DO NOT CROSS TWO FEMALES
Females are XX, males XY
Hemophilia Punnett Square
Hemophilia is x-linked recessive
Color blindness (X-linked recessive)
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.