Quiz 3

If a human gamete possessing one extra chromosome participates in fertilization with a normal human gamete, what will be the result? How many chromosomes will the zygote have?

A trisomy will be created for that chromosome. The zygote will have 47 chromosomes.

Many genetic disorders are caused by errors (mutations) in the genes on our chromosomes. Usually, in disorders caused by chromosomal abnormalities, the genes themselves are not mutated; rather, there are too many or too few of them. Why do you think that having too many or too few normal genes creates disorders?

Genes code for proteins and are responsible for producing all of the hormones, enzymes, and structural proteins that our bodies need. If there are too few or too many genes, too few or too many proteins will be produced, leading to disorders.

If a human gamete that is missing a chromosome participates in fertilization with a normal human gamete, what will be the result? How many chromosomes will the zygote have?

Monosomy will be created for that chromosome. The zygote will have 45 chromosomes.

If nondisjunction occurs in humans for one pair of homologous chromosomes during meiosis I, will any normal gametes result after meiosis II is complete? How many chromosomes will each gamete have?

No normal gametes will result. Two gametes will have an extra chromosome, for a total of 24 chromosomes. Two gametes will lack a chromosome and will possess only 22.

If nondisjunction occurs in humans for sister chromatids of one chromosome during meiosis II, will any normal gametes result? What chromosome number would each gamete have?

Yes, two gametes will be normal and will have 23 chromosomes. One gamete will be missing a chromosome and will have 22 chromosomes. One gamete will have an extra copy of a chromosome and will have a total of 24.