AP Biology : Understanding Meiosis

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #21 : Understanding Meiosis

When would the creation of a Down Syndrome gamete occur?

Possible Answers:

Telophase II

Prophase I

Anaphase I

Metaphase II

Correct answer:

Anaphase I

Explanation:

Down Syndrome results from trisomy 21, in which an individual has three copies of chromosome 21 in their genome. The cause for the extra chromosome is a nondisjunction event, resulting in an uneven splitting of the genome during meiosis.

Nondisjunction mainly occurs during meiosis I, particularly during anaphase I when homologous chromosomes are separated. When both chromosomes are pulled to the same pole the result of meiosis I is two cells, one with 22 chromosomes and one with 24. Meiosis II is used to segregate the sister chromatids of these cells, but does not change the amount of genetic material. When a gamete with 24 chromosomes fuses with a normal gamete with 23 chromosomes, the result is trisomy. When the trisomy particularly affects chromosome 21, the result is Down Syndrome.

Example Question #21 : Understanding Meiosis

Which of the following statements is true concerning meiosis?

Possible Answers:

Recombination occurs only during metaphase I

Daughter cells are haploid at the conclusion of both meiosis I and meiosis II

Cells are diploid at the end of meiosis I

Daughter cells are still genetically equivalent after meiosis I

During metaphase II, tetrads align at the equator of the cell

Correct answer:

Daughter cells are haploid at the conclusion of both meiosis I and meiosis II

Explanation:

Meiosis allows for the creation of genetically different haploid cells from one original germ cell. Following anaphase I, homologous chromosomes are separated from one another, resulting in a halving of the genetic material (haploid). As a result, the two cells are haploid following meiosis I. The separation of genetic material in anaphase II involves the splitting of chromatids, not homologous chromosomes. This does not affect the number of chromosomes in each cell, meaning all cells remain haploid.

Parent: diploid (XX)

Meiosis I: haploid, full chromosome (X)(X)

Meiosis II: haploid, single chromatid (/)(\)(/)(\)

Note that crossing over can only occur when the cell is diploid in meiosis I, specifically during prophase I.

Example Question #111 : Cellular Division

Why is there a reduction of ploidy after meiosis I?

Possible Answers:

Reduction of ploidy only occurs after mitosis

Reduction of ploidy only occurs after meiosis II

The two daughter cells after meiosis I each contain only half of the original cytoplasm

Pairs of homologous chromosomes are separated and placed in unique daughter cells

Sister chromatids are separated and placed in unique daughter cells

Correct answer:

Pairs of homologous chromosomes are separated and placed in unique daughter cells

Explanation:

Reduction of ploidy implies that the cell is losing a duplicate copy of each chromosome. In meiosis I, the cell segregates homologous chromosomes into two unique daughter cells. These daughter cells now technically only contain one copy of each chromosome. The parent cell contained two copies of each chromosome (diploid), while the daughter cells contain only one copy of each chromosome (haploid). This results in the reduction of ploidy after meiosis I.

After meiosis II, each cell contains only one chromatid. This chromatid, however, contains the code for a full chromosome, meaning that each daughter cell contains the genetic material for one chromosome. There is no reduction of ploidy after meiosis II, since both parent and daughter cells carry only one copy of each chromosome.

After mitosis, each cell contains one chromatid for each homologous chromosome. As such, the cells each contain DNA for two copies of each chromosome. Since both parent and daughter cells are diploid, there is no reduction of ploidy.

Example Question #24 : Understanding Meiosis

Which of the following is a correct statement about the difference between meiosis and mitosis? 

Possible Answers:

Mitosis produces two identical, diploid daughter cells after one division; meiosis produces four non-identical, haploid daughter cells after two divisions

Mitosis produces two identical, haploid daughter cells after one division; meiosis produces four non-identical, diploid daughter cells after two divisions

Mitosis produces four identical, diploid daughter cells after one division; meiosis produces two non-identical, haploid daughter cells after two divisions

Mitosis produces two non-identical, diploid daughter cells after one division; meiosis produces four identical, haploid daughter cells after two divisions

Mitosis produces two identical, diploid daughter cells after two divisions; meiosis produces four non-identical, haploid daughter cells after one division

Correct answer:

Mitosis produces two identical, diploid daughter cells after one division; meiosis produces four non-identical, haploid daughter cells after two divisions

Explanation:

Mitosis is used by somatic cells throughout the body. The goal of mitosis is to replace older cells with newer, healthier cells. In order for this replacement to be effective, the daughter cells must be identical to the parent cell. Somatic cells, or "body cells," are diploid, meaning that they carry two copies of each allele. Each round of mitosis produces two daughter cells after one division.

Meiosis only takes place in the gonads and is used to produce gametes. Gametes fuse to form a diploid zygote, but each individual gamete carries only half of the genetic information to form this zygote; as such, all gametes are haploid and carry only one copy of each allele. Gametes are not identical to the parent cell for this reason (the parent cell is diploid). Genetic variation (crossing over) can also occur during meiosis to enhance genetic diversity. Each round of meiosis produces four daughter cells after two divisions.

Example Question #25 : Understanding Meiosis

During what phase of meiosis do tetrads align along the equatorial plate?

Possible Answers:

Metaphase II

Prophase I

Metaphase I

Prophase II

Correct answer:

Metaphase I

Explanation:

Meiosis involves two cell divisions. During the first division, pairs of homologous chromosomes align at the center of the cell and are separated into two daughter cells. During the second division, single chromosomes align at the cell center (as they would during mitosis) and sister chromatids are separated into the daughter cells.

When homologous chromosomes align during the first division there are a total of four chromatids in each set, forming a tetrad. The alignment of chromosomes at the equatorial plate takes place during metaphase. Since we are looking at the alignment of chromosomes during the first meiotic division, the correct answer will be metaphase I.

Example Question #26 : Understanding Meiosis

What is the name of a pair of chromosomes that contains the same genes and loci?

Possible Answers:

Allele

Haploid chromosomes

Gene

Locus

Tetrad

Correct answer:

Tetrad

Explanation:

In prophase I, a process called synapsis involves the pairing of chromosomes. Chromosome pairs are referred to as a tetrad, homologous pair, or as bivalents.

Example Question #21 : Understanding Meiosis

During which phase of meiosis does chiasmata occur?

Possible Answers:

Metaphase I

Prophase I

Anaphase II

Prophase II

Anaphase II

Correct answer:

Prophase I

Explanation:

There are two events that occur in prophase I that do not occur in any other stage: chiasmata (crossing over) and synapsis (pairing of the chromosomes). Note that chiasmata does not occur during prophase of mitosis, but synapsis does occur.

Example Question #28 : Understanding Meiosis

Which of the following occur in both mitosis and meiosis?

Possible Answers:

Metaphase II

Separation of sister chromatids 

Prophase II

Recombination between homologous chromosomes

Recombination between sister chromatids

Correct answer:

Separation of sister chromatids 

Explanation:

The separation of sister chromatids is the only item of the answer choices that occurs in both mitosis and meiosis. Prophase II and metaphase II only occur in meiosis, as does recombination between homologous chromosomes. Recombination between sister chromatids does not occur (they are identical).

Example Question #29 : Understanding Meiosis

A human cell has 44 chromosomes and two X chromosomes. It is __________.

Possible Answers:

a somatic cell from a female

a gamete from a female

a sperm

a somatic cell from a male

an ovum

Correct answer:

a somatic cell from a female

Explanation:

Since the cell has 44 autosomes and two sex chromosomes it must be a somatic cell (2n=46). Two X chromosomes corresponds to a female so it must a somatic cell from a female. Sperm, and ova are the male and female gametes, which are haploid.

Example Question #30 : Understanding Meiosis

Meiosis in animals occurs in __________.

Possible Answers:

testes only

ovaries only

all cells in the animal's body

all somatic cells

both ovaries and testes

Correct answer:

both ovaries and testes

Explanation:

Meiosis is the form of cell division that results in gametes and so meiosis takes place in both ovaries and testes, which are the primary sex organs. Somatic cells undergo mitosis for cell division, which yields identical daughter cells that are diploid.  

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