CHP 25 Meiosis

If a diploid cell undergoes meiosis and produces two gametes that are normal, and one with n − 1 chromosomes, and one with n + 1 chromosomes, what type of error occurred?

A nondisjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell. Explanation: When this error occurs in meiosis II, only half of the gametes are affected.

What kind of cell results when a diploid and a haploid gamete fuse during fertilization?

A triploid cell Explanation: A triploid cell has three sets of chromosomes: the two from the diploid gamete and the one from the haploid gamete.

What is a nondisjunction?

An error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell. Explanation: Nondisjunction refers to the failure of pairs of chromosomes or sister chromatids to separate during meiosis or mitosis.

Which of the following accurately explains the relationship between crossing over and gene conversion?

Crossing over is the exchange of homologous portions of nonsister chromatids, creating new combinations of genetic material. Gene conversion is a process that may or may not occur during crossing over, and results in nonreciprocal recombination of genes when genes are very close together.

When can nondisjunction occur?

In meiosis, when homologous chromosomes fail to separate In mitosis, when sister chromatids fail to separate In meiosis, when sister chromatids fail to separate Explanation: Nondisjunction errors can occur in meiosis I, when homologous chromosomes fail to separate, or in either mitosis or meiosis II, when sister chromatids fail to separate

Which statement is INCORRECT? Members of a homologous pair have identical DNA sequences. A linkage group represents the genes on a particular chromosome. Genetic map distance is determined by recombination frequency. Homologous recombination involves formation of Holliday junctions.

Members of a homologous pair have identical DNA sequences.

During _____ a spindle forms in a haploid cell.

Prophase II Explanation: Prophase II is essentially the same as mitotic prophase except that the cells are haploid.

Which of these statements is INCORRECT? Metaphase I = bivalents align at equator. Anaphase II = sister chromatids separate. Prophase II = crossing over between homologous pairs. Anaphase I = homologues separate and move to opposite poles

Prophase II = crossing over between homologous pairs.

Of the following chromosomal abnormalities, which type is most likely to be viable in humans?

Trisomy Explanation: Some trisomies are viable in humans, but they result in developmental abnormalities, such as Down syndrome (trisomy 21). Only humans with trisomies of the small chromosomes (13, 18, or 21) or the sex chromosomes survive past birth.

Which syndrome is characterized by the XO chromosome abnormality?

Turner syndrome Explanation: Turner syndrome is characterized by a chromosome pattern of XO, or one X chromosome and no Y chromosome.

Homologous chromosomes migrate to opposite poles during _____.

anaphase I Explanation: During anaphase I sister chromatids remain attached at their centromeres, and homologous chromosomes move to opposite poles.

During _____ sister chromatids separate.

anaphase II Explanation: Anaphase II is essentially the same as mitotic anaphase except that the cell is haploid.

Meiosis II typically produces _____ cells, each of which is _____.

four ... haploid Explanation: At the end of meiosis II there are typically 4 haploid cells.

During _____ chromosomes align single file along the equator of a haploid cell

metaphase II Explanation: Metaphase II is essentially the same as mitotic metaphase except that the cell is haploid.

If a diploid cell undergoes meiosis and produces two gametes with n + 1 chromosomes and two gametes with n− 1 chromosomes, what type of error occurred?

nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell. Explanation: When this type of error occurs, half of the gametes receive one too many chromosomes, and the other half receive one too few. When all of the gametes are affected, the error probably occurred in meiosis I.

Synapsis occurs during _____

prophase I Explanation: Synapsis, the pairing of homologous chromosomes, occurs during prophase I.

The discovery of _____________ suggests that meiotic recombination is NOT uniform throughout the genome.

recombination hotspots

At the end of _____ and cytokinesis, haploid cells contain chromosomes that each consist of two sister chromatids.

telophase I Explanation: At the end of telophase I and cytokinesis, there are two haploid cells with chromosomes that consist of two sister chromatids each.

At the end of _____ and cytokinesis there are four haploid cells.

telophase II Explanation: At the end of telophase II and cytokinesis there are four haploid cells.

Meiosis I produces _____ cells, each of which is _____.

two ... haploid Explanation: At the end of meiosis I there are two haploid cells.