Assume that an organism exists in which crossing over does not occur, but that all other processes associated with meiosis occur normally. Consider how the absence of crossing over would affect the outcome of meiosis.

Question

If crossing over did not occur, which of the following statements about meiosis would be true? Select all that apply.
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The daughter cells of meiosis I would be diploid, but the daughter cells of meiosis II would be haploid.
Independent assortment of chromosomes would not occur.
There would be less genetic variation among gametes.
The four daughter cells produced in meiosis II would all be different.
The two sister chromatids of each replicated chromosome would no longer be identical.
The two daughter cells produced in meiosis I would be identical.

Answer 1

In the scenario where crossing over does not occur during meiosis, let's evaluate the truth of each statement listed regarding the outcomes of meiosis:

1. The daughter cells of meiosis I would be diploid, but the daughter cells of meiosis II would be haploid.

   • True. In meiosis I, homologous chromosomes are separated, and the daughter cells are still diploid (2n). In meiosis II, which resembles mitosis, the sister chromatids are separated, resulting in haploid (n) daughter cells.

2. Independent assortment of chromosomes would not occur.

   • False. Independent assortment can still occur in this scenario. It refers to the random distribution of maternal and paternal chromosomes to the gametes at meiosis I, which is independent of crossing over.

3. There would be less genetic variation among gametes.

   • True. Since crossing over is a source of genetic variation by shuffling alleles between homologous chromosomes, its absence would result in less genetic variability among the gametes produced.

4. The four daughter cells produced in meiosis II would all be different.

   • False. Without crossing over, the four daughter cells, though haploid, would likely have the same combination of alleles as the original homologous chromosomes contributed by the parents, hence they would not all be different.

5. The two sister chromatids of each replicated chromosome would no longer be identical.

   • False. The sister chromatids are formed during DNA replication and remain identical (barring mutations) until they are separated during meiosis II.

6. The two daughter cells produced in meiosis I would be identical.

   • True. Since there is no crossing over, the homologous chromosomes are simply segregated into daughter cells, resulting in the two daughter cells of meiosis I being genetically identical.

In summary, the true statements in this context would be:

• The daughter cells of meiosis I would be diploid, but the daughter cells of meiosis II would be haploid.
• There would be less genetic variation among gametes.
• The two daughter cells produced in meiosis I would be identical.