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CHAPTER 12 SEX-LINKED TRAITS
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Karyotype: a picture of chromosomes.
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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
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Is it Male or Female? Explain
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Sex chromosomes: determines the sex of the individual.
The sex chromosomes are the 23rd pair of chromosomes. XX =female
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XY=male
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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.
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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.
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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.
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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
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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
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Now You Try Cross a carrier female with a male with hemophilia.
__ XHXh __ X __ XhY ___
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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
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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.
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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.
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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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