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Sex-Linked Genes

Sex-Linked Genes. Sex-Linked Genes. Female sex chromosomes: XX Male sex chromosomes: XY Sex-linked genes are genes that are carried on the sex chromosomes (specifically the X chromosome) Sex-linked traits are traits that are controlled by the sex-linked genes

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Sex-Linked Genes

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  1. Sex-Linked Genes

  2. Sex-Linked Genes • Female sex chromosomes: XX • Male sex chromosomes: XY • Sex-linked genes are genes that are carried on the sex chromosomes (specifically the X chromosome) • Sex-linked traits are traits that are controlled by the sex-linked genes • A carrier is a person who has one recessive allele and one dominant allele (only females can be carriers) • Carriers of a trait do not exhibit the trait, but they can pass it on to their offspring • Males are more likely to exhibit a sex-linked trait, because they only have one X chromosome

  3. Sex linked genes are written as follows: • Male with trait=XtY Female Carrier=XTXt • Normal Male=XTY Female with trait=XtXt • Normal female=XTXT • Colorblindness is an example of a sex-linked trait • Males are more likely to have red/green colorblindness than females

  4. Example Problem: A woman who is a carrier for the colorblindness gene (XCXc) marries a man who has regular color vision (XCY). They have 4 children. Assuming ideal conditions, list the four children’s genotypes and phenotypes. XCXc 1 Female w/ Normal Vision (XCXC) 1 Female Carrier (XCXc) 1 Male w/Normal Vision (XCY) 1 Male w/Colorblindness (XcY) XC Y

  5. Karyotype • A karyotype is a picture of all the chromosomes from an individual’s cells • Normal human body cells have 46 chromosomes in 23 pairs Normal Genetic Disorder: Trisomy 21

  6. Practice Problems • A man who has hemophilia (XhY) has children with a woman who does not have hemophilia (XHXH). Can any of their children have hemophilia? Create a Punnett Square and explain your answer. • A woman who is a carrier for albinism (XAXa) has children with a man who does not have albinism (XAY). What are the possible phenotypes of their children?

  7. Test Review – Copy & Answer in Your Notebooks. • 1. Know all the vocabulary words!! • 2. Compare sexual and asexual reproduction. • 3. Compare mitosis and meiosis. • 4. What are gametes? What is unique about the # of chromosomes in gametes? • 5. What are the male and female gametes called? • 6. Compare haploid and diploid cells? • 7. Humans have how may total chromosomes? • 8. Compare dominant and recessive alleles.

  8. 9. Compare homozygous and heterozygous alleles. • 10. Compare genotype and phenotype? • 11. Punnett squares – be able to complete them and give ratios of genotypes and phenotypes. • A) One cat carries heterozygous, long-haired traits (Ss), and its mate carries homozygous short-haired traits (ss) . • B) The female dog is heterozygous for spots. The male dog is heterozygous for spots. Having spots is dominant to no spots. Figure out the phenotypes and genotypes of their possible puppies by using a Punnett Square.

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