CHAPTER 12 SEXLINKED TRAITS EQ How can I

CHAPTER 12 SEX-LINKED TRAITS EQ: How can I determine the inheritance of a sex-linked trait?

Body Cells vs. Sex Cells l Autosomes: the first 22 homologous pairs of chromosomes. l Autosomes are the same for both males and females. l Sex cells: Determine sex of offspring

Is it Male or Female? Explain

l Sex chromosomes: determines the sex of the individual. l. The sex chromosomes are the 23 rd pair of chromosomes. l. XX =female

XY=male

Which parent determines the sex of an offspring? l DAD l Why? All moms have the genotype XX. When egg cells are made, they will all carry a single X chromosome.

All dads have the genotype XY. When sperm cells are made, 50% will have an X chromosome and 50% will have a Y chromosome. l Therefore, males and females are born in roughly a 50: 50 ratio. l

SEX-LINKED TRAITS l l Those traits that are controlled by genes on the X or Y chromosomes. NOTE: The Y chromosome is much smaller than the X chromosome and only contains a few genes. Most sex-linked traits are on the X chromosome.

In humans, hemophilia is a sex-linked trait. Having hemophilia is recessive (Xh) to being normal (XH). The heterozygous female is called a carrier. Cross a carrier female with a normal male. __ XHXh __ XHY ___ male X H Y XH Xh XH Y Xh Y

Results: Genotypic ratio: 1 XHXH : 1 XHXh : 1 XHY : 1 Xh Y XH Phenotypic ratio: 2 normal females: H XH H 1 normal male: X X Normal Female 1 male with hemophilia Y XH Y Normal Male Xh XH Xh Normal Female Xh Y Male w/ hemophilia

Now You Try l Cross a carrier female with a male with hemophilia. __ XHXh __ Xh. Y ___

Results: Genotypic ratio: 1 XHXh : 1 Xh. Xh : 1 XHY : 1 Xh Y XH Phenotypic ratio: 1 normal female: Xh X H XH XH Xh Xh Y XH Y Xh Y 1 female w/ Hemopholia: 1 normal male: 1 male with hemophilia Normal Female Normal Male Female w/ hemophilia Male w/ hemophilia

Genetic Sex-Linked Disorders Color Blindness l l l Cause: x-linked recessive 1/10 males have, 1/100 females have. Why the difference? Individuals are unable to distinguish shades of red-green.

Genetic Sex-Linked Disorders 2 - Hemophilia A and B Recessive disorders that affect 1 of 5, 000 males. These interfere with normal blood clotting and occur on the X chromosome.