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SEX-LINKED TRAITS

Learn about sex-linked traits controlled by X or Y chromosomes in the human karyotype, with examples like hemophilia and colorblindness. Discover how gender is determined and why certain traits are more common in males.

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SEX-LINKED TRAITS

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  1. SEX-LINKED TRAITS

  2. Karyotype: a picture of chromosomes.

  3. … Autosomes: the first 22 homologous pairs of chromosomes. • Autosomes are the same for both males and females.

  4. Sex chromosomes: determines the sex of the individual. • The sex chromosomes are the 23rd pair of chromosomes.

  5. XX = female

  6. XY = male

  7. Which parent determines the sex of an offspring? DAD

  8. Why? • All moms have the genotype XX. When egg cells are made, they will all carry a single X chromosome.

  9. 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.

  10. 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.

  11. 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. XHXhX _____

  12. 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. XHXhX XHY

  13. Genotypic ratio: 1 XHXH :1XHXh :1XHY :1XhY Phenotypic ratio: 2 normal females: 1normal male: 1 male with hemophilia

  14. Cross a carrier female with a male with hemophilia. XHXhX _____

  15. Cross a carrier female with a male with hemophilia. XHXhX XhY

  16. Genotypic ratio: 1 XHXh :1XhXh :1XHY :1XhY Phenotypic ratio: 1 normal female: 1 female with hemophilia:1 normal male: 1 male with hemophilia

  17. In humans, red-green colorblindness is a sex-linked trait. People with red-green colorblindness can not tell the difference between red and green. Colorblindness is the result of a recessive allele. Cross a female with colorblindness with a male with normal vision. XnXnX _____

  18. In humans, red-green colorblindness is a sex-linked trait. People with red-green colorblindness can not tell the difference between red and green. Colorblindness is the result of a recessive allele. Cross a female with colorblindness with a male with normal vision. XnXnX XNY

  19. Genotypic ratio: 2 XNXn : 2 XnY Phenotypic ratio: 2 normal females: 2 males with colorblindness

  20. Why are sex-linked traits more common in males than in females? • Because a male only has to inherit ONE recessive allele in order to get a sex-linked trait and a female has to inherit TWO recessive alleles in order to acquire the sex-linked trait.

  21. It is easier to inherit one recessive allele than two. If the female only inherits one recessive allele, then they are a carrier but have the normal phenotype.

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