Chapter 2.3. Animation Activity: Genetic Variation in Meiosis

2

Correct. Although there are two rounds of cell division in meiosis and cells go from being diploid to haploid, neither of these two features automatically results in genetic differences among cells. Genetic diversity among meiotic products (gametes) is generated by both independent assortment of homologous chromosomes on the metaphase plate, and crossing over of non-sister chromatids.

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Incorrect. Although there are two rounds of cell division in meiosis and cells go from being diploid to haploid, neither of these two features automatically results in genetic differences among cells. Genetic diversity among meiotic products (gametes) is generated by both independent assortment of homologous chromosomes on the metaphase plate, and crossing over of non-sister chromatids.

2

Correct. Paired homologous chromosomes line up on the metaphase plate during meiosis I, but the arrangement of paternally and maternally derived chromosomal homologs is random with respect to which chromosome will go to the right or left of the metaphase plate. This random arrangement of paternally and maternally derived chromosomes is the mechanism of independent assortment.

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Incorrect. Paired homologous chromosomes line up on the metaphase plate during meiosis I, but the arrangement of paternally and maternally derived chromosomal homologs is random with respect to which chromosome will go to the right or left of the metaphase plate. This random arrangement of paternally and maternally derived chromosomes is the mechanism of independent assortment.

2

Correct. Non-sister chromatids undergo crossing over during prophase I. This is the stage when homologous chromosomes initiate pairing. Although the homologous chromosomes remain associated until anaphase I, all genetic exchange between homologs is restricted to prophase I.

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Incorrect. Non-sister chromatids undergo crossing over during prophase I. This is the stage when homologous chromosomes initiate pairing. Although the homologous chromosomes remain associated until anaphase I, all genetic exchange between homologs is restricted to prophase I.

2

Correct. If there are only two homologous chromosomes, it is obvious that only two arrangements are possible (either the maternally or paternally derived homolog will be on the right with equal probability). This eliminates “A” and “C” as possibilities, but all other choices still fit the observation. If there are two homologous chromosome pairs, there are four possible arrangements of chromosomes on the metaphase plate during meiosis one leaving “B,” “D,” and “E” as viable answers. However in the case of three homologous chromosome pairs, there are eight possible arrangements of chromosomes on the metaphase plate during meiosis I (see this for yourself in the animation). Only choice “D” fits this observation, and is, in fact, the correct formula.

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Incorrect. If there are only two homologous chromosomes, it is obvious that only two arrangements are possible (either the maternally or paternally derived homolog will be on the right with equal probability). This eliminates “A” and “C” as possibilities, but all other choices still fit the observation. If there are two homologous chromosome pairs, there are four possible arrangements of chromosomes on the metaphase plate during meiosis one leaving “B,” “D,” and “E” as viable answers. However in the case of three homologous chromosome pairs, there are eight possible arrangements of chromosomes on the metaphase plate during meiosis I (see this for yourself in the animation). Only choice “D” fits this observation, and is, in fact, the correct formula.

2

Correct. The number of different chromosomal arrangements possible through independent assortment can be calculated using the formula 2ⁿ, where n represents the number of homologous chromosome pairs. Therefore a diploid organism with 12 chromosomes would have six homologous pairs leading to 64 possible chromosomal arrangements on the metaphase plate during meiosis I.

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Incorrect. The number of different chromosomal arrangements possible through independent assortment can be calculated using the formula 2ⁿ, where n represents the number of homologous chromosome pairs. Therefore a diploid organism with 12 chromosomes would have six homologous pairs leading to 64 possible chromosomal arrangements on the metaphase plate during meiosis I.

2

Correct. When homologous chromosomes pair in prophase I, each chromosome consists of two identical sister chromatids. Each chromatid is a single molecule of DNA consisting of two antiparallel DNA strands. Therefore paired homologous chromosomes consist of four chromatids made up of eight strands of DNA.

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Incorrect. When homologous chromosomes pair in prophase I, each chromosome consists of two identical sister chromatids. Each chromatid is a single molecule of DNA consisting of two antiparallel DNA strands. Therefore paired homologous chromosomes consist of four chromatids made up of eight strands of DNA.

2

Correct. Crossing over normally occurs only between homologous paired chromosomes in the same meiotic cell.

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Incorrect. Crossing over normally occurs only between homologous paired chromosomes in the same meiotic cell.

2

Correct. Homologous chromosome pairs, that first joined in prophase I, line up on the metaphase plate in metaphase I. These chromosome pairs separate during anaphase I, while chromosomes line up on the metaphase plate individually during metaphase II and centromeres joining sister chromatids divide creating new chromosomes during anaphase II.

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Incorrect. Homologous chromosome pairs, that first joined in prophase I, line up on the metaphase plate in metaphase I. These chromosome pairs separate during anaphase I, while chromosomes line up on the metaphase plate individually during metaphase II and centromeres joining sister chromatids divide creating new chromosomes during anaphase II.

2

Correct. A single crossover event involves only two of the four homologous chromatids in a paired set of homologous chromosomes. At the conclusion of the event two of the four chromatids are recombinant while the other two remain non-recombinant.

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Incorrect. A single crossover event involves only two of the four homologous chromatids in a paired set of homologous chromosomes. At the conclusion of the event two of the four chromatids are recombinant while the other two remain non-recombinant.

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Correct. Although each crossover event will only generate two recombinant chromatids from a homologous chromosome pair, two independent crossover events involving two sets of non-sister chromatids in a single homologous chromosome pair will generate four recombinant chromosomes at the completion of meiosis.

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Incorrect. Although each crossover event will only generate two recombinant chromatids from a homologous chromosome pair, two independent crossover events involving two sets of non-sister chromatids in a single homologous chromosome pair will generate four recombinant chromosomes at the completion of meiosis.