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

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

Is it Male or Female? Explain

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

XY=male

Which parent determines the sex of an offspring? DAD 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 All dads have the genotype XY. When sperm cells are made, 50% will have an X chromosome and 50% will have a Y chromosome. Therefore, males and females are born in roughly a 50:50 ratio.

SEX-LINKED TRAITS 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.

XH Xh XH XH XH Xh XH Y XH Y Xh Y male 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. XH Xh __ XHXh __  X  __ XHY ___ XH XH XH Xh XH Y male XH Y Xh Y

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

Now You Try Cross a carrier female with a male with hemophilia. __ XHXh __  X  __ XhY ___

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

Genetic Sex-Linked Disorders Color Blindness 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.