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Human Chromosomes Section 14–2

Human Chromosomes Section 14–2 . This section describes the structure of human chromosomes. It also describes genetic disorders that are sex-linked, as well as disorders caused by nondisjunction. Human Genes and Chromosomes .

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Human Chromosomes Section 14–2

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  1. Human Chromosomes Section 14–2 This section describes the structure of human chromosomes. It also describes genetic disorders that are sex-linked, as well as disorders caused by nondisjunction.

  2. Human Genes and Chromosomes Circle the letter of each sentence that is true about human genes and chromosomes. • Chromosome 22 contains long stretches of repetitive DNA that do not code for proteins. • Human genes located close together on the same chromosome tend to be inherited together.

  3. Sex-Linked Genes What are sex-linked genes? • They are genes that are located on the X or Y chromosomes.

  4. Is the following sentence true or false? The Y chromosome does not contain any genes at all. False

  5. Complete the compare-and-contrast table for sex-linked genes.

  6. Is the following sentence true or false? • All X-linked alleles are expressed in males, even if they are recessive. • true

  7. Punnett Square below illustrates color blindness inheritance.

  8. X-Chromosome Inactivation • How does the cell “adjust” to the extra X chromosome in female cells? • In female cells, one X chromosome is switched off.

  9. What is a Barr body? • It is a dense region in the nucleus that is formed by the turned-off Xchromosome.

  10. Is the following sentence true or false? • Barr bodies are found only in males.

  11. If you saw a white cat with orange and black spots, is it most likely a male or a female? • It’s probably a female. In cells in some parts of the body, one X chromosome that has the allele for orange spots is switched off, whereas in cells in other parts of the body, the other X chromosome with the allele for black spots is switched off.

  12. Chromosomal Disorders What occurs during nondisjunction? • Homologous chromosomes fail to separate during meiosis.

  13. Chromosomal Disorders Is the following sentence true or false? • If nondisjunction occurs, gametes may have abnormal numbers of chromosomes. • True

  14. Chromosomal Disorders • The condition in which an individual has three copies of a chromosome is known astrisomy , which means “three bodies.”

  15. Chromosomal Disorders • Is the following sentence true or false? • Down syndrome occurs when an individual has two copies of chromosome 21 • False

  16. Circle the letter of the characteristic of Down syndrome. b. mental retardation

  17. Chromosomal Disorders Why does an extra copy of one chromosome cause so much trouble? • Scientists do not exactly know for sure.

  18. Chromosomal Disorders Circle the letter of each sentence that is true about sex chromosome disorders. • A female with the karyotype 45,X has inherited only one X chromosome andis sterile. • The Y chromosome contains a sex-determining region that is necessary for male sexual development.

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