2 Human Blood TypesHuman Blood Types have a gene that displays multiple alleles and codominanceThe gene has three alleles:A codes for an A antigen (protein) on red blood cellsB codes for a B antigen (protein) on red blood cellsO 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 GenotypesType A blood AA or AOType B blood BB or BOType AB blood ABType O blood OO
6 Sex-linked Genes Sex-linkage Gene for trait is found on a sex chromosomeMost (almost all) are found on the X chromosome; there are very few Y-linked disordersCan be sex-linked dominant or sex-linked recessive
9 X-linked Genotypes and Phenotypes Genotypes of each parent are written as superscripts on their sex chromosomesEx: H=“healthy” allele; h= hemophilia alleleXHXh female carrier of hemophiliaXHXH female w/o hemophiliaXhXh female with hemophiliaXHY male w/o hemophiliaXhY male with hemophilia
10 Sex-linked Punnett Squares DO NOT CROSS TWO FEMALESFemales are XX, males XY
11 Hemophilia Punnett Square Hemophilia is x-linked recessive
13 X-linked Recessive Disorders Show up more in malesFemales have two X chromosomesrare to inherit two “bad” X’s to show disorderOne “good” X masks the “bad” X; healthy dominant allele masks the recessive alleleMale have only one X chromosomeMales 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.