The cathas 36 pairs of chromosomes in its somatic cells.

Question

(a) Howmany chromosomes are present in a cat's spermcells?
(b) Howmany sister chromatids are present in a cell that is entering thefirst meiotic division? (c) In a cell that is entering the secondmeiotic division?

Facts and concepts:
1. Chromosomes come in pairs - that is, there are two homologouschromosomes in each pair.
2. Chromosome duplication creates two sister chromatids for eachchromosome in the cell.
3. The first meiotic division reduces the number of duplicatedchromosomes (and the number of sister chromatids present) by afactor of two.
4. The second meiotic division reduces the number of sisterchromatids by another factor of two. (b) Howmany sister chromatids are present in a cell that is entering thefirst meiotic division? (c) In a cell that is entering the secondmeiotic division?

Facts and concepts:
1. Chromosomes come in pairs - that is, there are two homologouschromosomes in each pair.
2. Chromosome duplication creates two sister chromatids for eachchromosome in the cell.
3. The first meiotic division reduces the number of duplicatedchromosomes (and the number of sister chromatids present) by afactor of two.
4. The second meiotic division reduces the number of sisterchromatids by another factor of two.

Explanation / Answer

(a) Since sperm cell is not somatic cell, therefore there is only18 pairs of chromosomes. (b) Before first meiotic division, there is DNA replication, so theamount of chromsome become doubled. Therefore, number of sisterchromatids = 72 (c) In a cell that is entering the second meiotic division, thenumber of sister chromatids become halved. Therefore, the number ofsister chromatids = 36 (AFTER 2nd meiotic division, the number ofsister chromatids become 36/2 = 18) Hope this helps!

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