Blood Types and Blood Types and Sex-linkageSex-linkage

Human Blood TypesHuman Blood Types

Human Blood Types have a gene that Human Blood Types have a gene that displays displays multiple alleles multiple alleles and and codominancecodominance

The gene has three alleles:The gene has three alleles:– A codes for an A codes for an A antigen A antigen (protein) on red (protein) on red

blood cellsblood cells– B codes for a B codes for a B antigen B antigen (protein) on red blood (protein) on red blood

cellscells– O codes for O codes for no antigen no antigen on red blood cellson red blood cells

The A and B alleles are The A and B alleles are codominantcodominant

O allele is O allele is recessiverecessive

Blood Type Phenotypes and Blood Type Phenotypes and GenotypesGenotypes

PhenotypesPhenotypes GenotypesGenotypes

Type A blood Type A blood AA or AOAA or AO

Type B blood Type B blood BB or BOBB or BO

Type AB blood Type AB blood ABAB

Type O blood Type O blood OOOO

Blood Type AntigensBlood Type Antigens

Sex-linked GenesSex-linked Genes

Sex-linkageSex-linkage– Gene for trait is found on a sex chromosomeGene for trait is found on a sex chromosome– Most (almost all) are found on the Most (almost all) are found on the X X

chromosomechromosome; there are very few Y-linked ; there are very few Y-linked disordersdisorders

– Can be sex-linked Can be sex-linked dominantdominant or sex-linked or sex-linked recessive recessive

Inheritance of X-linked Inheritance of X-linked recessive disorderrecessive disorder

Inheritance of X-linked Inheritance of X-linked recessive disorderrecessive disorder

X-linked Genotypes and X-linked Genotypes and PhenotypesPhenotypes

Genotypes of each parent are written as Genotypes of each parent are written as superscripts on their sex chromosomessuperscripts on their sex chromosomes– Ex: H=“healthy” allele; h= hemophilia alleleEx: H=“healthy” allele; h= hemophilia allele

XXHHXXh h female carrier of hemophilia

XHHXXHH female w/o hemophiliafemale w/o hemophilia

XhXh female with hemophilia

XHY male w/o hemophilia

XhY male with hemophilia

Sex-linked Punnett SquaresSex-linked Punnett Squares

DO NOT CROSS TWODO NOT CROSS TWO FEMALES FEMALES

Females are XX, males XYFemales are XX, males XY

Hemophilia Punnett SquareHemophilia Punnett SquareHemophilia is x-linked recessiveHemophilia is x-linked recessive

Color blindness Color blindness (X-linked recessive)(X-linked recessive)

X-linked Recessive DisordersX-linked Recessive Disorders

Show up more in malesShow up more in males– Females have two X chromosomesFemales have two X chromosomes

rare to inherit two “bad” X’s to show disorderrare to inherit two “bad” X’s to show disorder

One “good” X masks the “bad” X; One “good” X masks the “bad” X; healthy dominant healthy dominant allele masks the recessive alleleallele masks the recessive allele

– Male have only one X chromosomeMale have only one X chromosomeMales only need Males only need one recessive alleleone recessive allele to show the to show the trait b/c they don’t have another X which could trait b/c they don’t have another X which could carry a healthy dominant allele to carry a healthy dominant allele to maskmask the the recessive allele.recessive allele.