SexLinked Genes and Pedigrees Linked Genes Some genes

Linked Genes Some genes are linked because they are on the SAME chromosome. A

• • Sex-linked Traits can be either Autosomal: traits (genes) are located on

Examples of Autosomal Traits Autosomal Dominant: Huntington’s Disease Achondroplasia (Dwarfism) Osteoporosis Autosomal Recessive: Cystic

Examples of Sex-Linked Traits X-linked Recessive: Colorblindness Hemophilia Duchenne Muscular Dystrophy Y-linked: Ear Hair

What this means… Males have only one X chromosome, so ALL X-linked alleles are

Sex-linked Traits Example: Eye color in fruit flies Sex Chromosomes fruit fly eye color

Sex-linked Trait Problem Example: Eye color in fruit flies (red-eyed male) x (white-eyed female)

Sex-linked Trait Solution: Xr XR XR Xr Y Xr XR Xr Xr Y 50%

Carriers Heterozygote (has the recessive allele but the trait is NOT expressed) In autosomal

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Sex-Linked Genes and Pedigrees

Linked Genes Some genes are linked because they are on the SAME chromosome. A chromosome is a set of linked genes. Remember: Offspring get one copy of each chromosome from each parent. Chromosomes assort independently, NOT individual genes. Crossing-over during meiosis can “unlink” genes.

• • Sex-linked Traits can be either Autosomal: traits (genes) are located on the non-sex chromosomes Sex-Linked: traits (genes) are located on the sex chromosomes Sex chromosomes are X and Y XX genotype for females XY genotype for males Many sex-linked traits are carried on X chromosome copyright cmassengale 3

Examples of Autosomal Traits Autosomal Dominant: Huntington’s Disease Achondroplasia (Dwarfism) Osteoporosis Autosomal Recessive: Cystic Fibrosis Sickle Cell Anemia

Examples of Sex-Linked Traits X-linked Recessive: Colorblindness Hemophilia Duchenne Muscular Dystrophy Y-linked: Ear Hair

X vs. Y

What this means… Males have only one X chromosome, so ALL X-linked alleles are expressed in males, even if the trait is recessive. This is why males exhibit some traits more frequently than females. X-linked traits are passed from mother to son Y-linked traits are passed from father to son

Sex-linked Traits Example: Eye color in fruit flies Sex Chromosomes fruit fly eye color XX chromosome - female XY chromosome - male copyright cmassengale 8

Sex-linked Trait Problem Example: Eye color in fruit flies (red-eyed male) x (white-eyed female) X RY x X r Remember: the Y chromosome in males does not carry an allele for the rtrait. r X X RR = red eyed Rr = red eyed R X rr = white eyed XY = male Y XX = female copyright cmassengale 9

Sex-linked Trait Solution: Xr XR XR Xr Y Xr XR Xr Xr Y 50% red eyed female 50% white eyed male copyright cmassengale 10

Pedigrees

Carriers Heterozygote (has the recessive allele but the trait is NOT expressed) In autosomal traits, carriers can be Male or Female. In Sex-Linked traits, ONLY Females can be carriers. All Sex-Linked traits are expressed in Males. copyright cmassengale 12