You are still in South America collecting data on the new rodent species you dis

Question

You are still in South America collecting data on the new rodent
species you discovered last week. You have recently discovered
that these rodents have 30 chromosomes in their somatic cells.
Using your knowledge of meiosis, explain what would happen
to subsequent generations of this rodent if the chromosome
number was not reduced during meiosis. Address the following
topics: Discuss the number of chromosomes in the rodent’s
gametes. Discuss the process of meiosis. Explain how meiosis
conserves the diploid chromosome number from one generation
to the next. Explain what would happen without meiosis

Explanation / Answer

Rodent somatic cells, like ours, are diploid, so 2N=30 chromosomes. The gametes, after meiosis I, are haploid, meaning N=15 chromosomes (normally). Normal Meiosis I: Chromosomes replicate (get sister chromatids), homologous chromosomes find each other (15 pairs of homologous chromosomes), then the homologous chromosomes separate. You end up with 2 cells with half the chromosome number (15) but these chromosomes are replicated (have sister chromatids), so they undergo meiosis 2... Normal Meiosis II: 2 cells with 15 chromosomes each line up the chromosomes (metaphase plate) and separate the sister chromatids. You end up with 4 gametes with half the chromosome number as somatic cells. Because these gametes have half the normal somatic chromosome number, 2 gametes from 2 different organisms can combine to make a diploid, or "normal", somatic cell (thereby conserving chromosome number from generation to generation). Without meiosis, you couldn't reduce the chromosome number in gametes, so that the combination of 2 cells would produce twice the number of chromosomes, and organisms would contain more and more chromosomes as generations continued... which of course would not work for cells.

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