Pedigrees and Sex Linked Traits Pedigree sex linked

Pedigrees and Sex Linked Traits

Pedigree/ sex linked traits outline I. Pedigree circle= square = shaded= unshaded= half shaded = horizontal lines= vertical lines= roman numeral= Autosomes III. Sex chromosomes IV. Karyotype V. sex-linked traits II. more common in: why: diseases: examples of crosses

n Family Tree—traces a family name and family members through successive generations

n Pedigree—a graphic representation of genetic inheritance – helps identify sex of individual, individuals who are affected by a trait, and family relationships

n In a Pedigree… – Circle—Female – Square—Male

n Shaded circles and squares—individuals showing the trait being studied in pedigree n Unshaded circles and squares—individuals who do not show the trait being studied n Half-shaded circle or square—represents a carrier (heterozygous individual)

n Horizontal line— connects parents n Vertical line—connects parents to offspring n Roman numeral— shows generations Arabic numbers (1, 2, 3, etc…)—shows individuals n Rows= generations n

n Recessive trait—in a pedigree the trait appears to skip a generation n Individuals I 1 and I 2 —both must be carriers of the trait, because they have an offspring with the trait

n Individual II 1— probably not a carrier because no one in generation III has the trait n Individuals III 3 and III 4—both carriers because 2 individuals in generation IV are affected for trait

n Dominant trait—In a pedigree the trait usually appears in every generation – Remember—with a dominant trait, individuals only need to be heterozygous to be affected

n Individual I 2— heterozygous, because not all offspring are affected n Individual II 4— heterozygous because none of the offspring are affected

n Autosomes— 1 st 22 pairs of chromosomes in a human (all chromosomes that are not sex ones) n Sex chromosomes--23 rd (last) pair of chromosomes – Ex. XX-female XY-male • The male always determines sex of offspring

22 Autosomes Sex chromosomes

�Karyotype: chart showing all pairs of chromosomes in a human, used to show chromosomal disorders How would this karyotype look if the individual had trisomy 21? There would by 3 copies of chromosome 21

n Sex-linked traits--traits located on sex chromosomes (XX = female, XY = male

Sex linked disorders n More common in males because if carried on X chromosome, males only have one copy, if they receive bad copy, they have the disorder n Since females have 2 X’s, if they receive one bad copy, there’s still a chance of having a normal X cover it n Ex. color blindness, hemophilia

n Cross normal male and heterozygous female N = normal vision n = colorblind XN Y XN X NX N X NY Xn X NX n X n. Y Phenotypic ratio--Female: 100% normal (50% carriers) Male: 50% normal 50% colorblind

n Cross normal male and hemophiliac female H = normal blood h = hemophiliac XH Y Xh X HX h X h. Y Phenotypic ratio--Female: 100% normal (50% carriers) Male: 100% hemophiliac