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CHAPTER 12 SEX-LINKED TRAITS

CHAPTER 12 SEX-LINKED TRAITS. Karyotype: a picture of chromosomes. 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.

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CHAPTER 12 SEX-LINKED TRAITS

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  1. CHAPTER 12 SEX-LINKED TRAITS

  2. Karyotype: a picture of chromosomes.

  3. 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

  4. Is it Male or Female? Explain

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

  6. XY=male

  7. 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.

  8. 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.

  9. 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.

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

  11. XH Xh 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 Xh Normal Female XH XH Normal Female Xh Y Male w/ hemophilia XH YNormal Male

  12. Now You Try • Cross a carrier female with a male with hemophilia. __ XHXh__  X  __ XhY ___

  13. XH Xh XH Y 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 XH Normal Female Xh Y Male w/ hemophilia XH YNormal Male

  14. 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.

  15. 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.

  16. Polygenic Inheritance • Traits that are influenced by several Genes. • Show many degrees of variation. Examples: • Height • Hair color • Skin Color • Eye Color

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