Question

Cats are diploid organisms that have 38 chromosomes in their somatic cells during G1 phase. Based on this information, answer the following questions about the cell cycle of a cat's somatic cell: a) How many DNA double helix molecules are present in a somatic cell of a cat during G1 phase? Explain your answer. b) How many total DNA double helix molecules are present in a somatic cell of a cat during G2 phase? Explain your answer. c) Describe what a single chromosome in G2 phase will look like. Include whether it is condensed what it will be composed of. d) How many total chromatids will there be in a somatic cell of a cat during G2 phase? Explain your answer. e) After a cat's somatic cell finishes cytokinesis, how many chromosomes will be present in each of the daughter cells? Explain your answer. For part f: a biologist sequences the entire genome of the DNA within different cells from different parts of a cat'sbody. Specifically, the biologist compares the DNA sequences from a brain cell with that of a cell from the cat's intestine. f) Would you expect that the DNA sequences from these two cells would be the same or different? (Assume they're both in the same phase of the cell cycle). Explain your answer.

Answer 1

the cell cycle progress as G1, S, G2 and M phase, during S phase the DNA replicates and the two double-stranded DNA molecules are attached to each other at the centromere. so each chromosome will have 2 sister chromatids attached to each other at the centromere.

a) the number of DNA double helices in the G1 phase= number of chromosomes= 38.( DNA is not in the replicated state, so number of DNA molecules=38)

b) number of DNA double helices in the G2 phase = 2$\times$ number of chromosomes= 2$\times$38= 76 ( DNA is replicated during S phase so there are 2$\times$38 DNA molecules present in the cell)

c) the chromosome in the G2 have 2 sister chromatids attached to each other at the centromere and the chromatids are not in the condensed state, the DNA is wrapped around the histone proteins and it appear as beads on ring.

chromatid centromere

chromatin is not shown as beads on ring in the image.

d) number of chromatids in the G2 phase= 2$\times$ number of chromosomes= 2$\times$38= 76 ( DNA is replicated during S phase so there are 2$\times$38 chromatids are present in the cell)

e) somatic cells undergo mitosis, mitosis is the equational division that is the number of chromosomes in the daughter cells and the parent cells are the same.

so total number of chromosomes in the daughter cell = 38.

f) the DNA sequence in the daughter cells will be same, the DNA is replicated during S phase, then during prophase, the chromatids condense to form chromosomes, the chromosomes have 2 sister chromatids attached to each other at the centromere, then the chromosomes align at the metaphase plate during the metaphase then during anaphase the sister chromatids are separated and moves to opposite poles, then by telophase the chromatids reach the poles and then nuclear envelope reforms.

the daughter cells have the same genetic material as the parent cell.