In a tissue sample of 140 cells, 7 cells are in the last stage of mitosis. One complete cell cycle in this tissue takes 1600 minutes. How long does the
last stage in mitosis take for an average cell in this tissue?

Explanation:

1. If an organism has 15 pairs of homologous chromosomes, how many chromosomes will each

daughter cell have after telophase of mitosis? In this same organism, how many chromosomes will

each daughter cell have after telophase II of meiosis?

n

2n n

2n 2n

2n n

n

Mitosis Meiosis

If a cell has 15 pairs of chromosomes (n = 15), it has 30 chromosomes (2n = 30). At the

end of mitosis, the two daughter cells will be exact copies of the original cell. Each daughter

cell will have 30 chromosomes. At the end of meiosis II, each cell (i.e., gamete) would have

half the original number of chromosomes, that is, 15 chromosomes.

2. How many DNA molecules are present in a chromosome of a cell in metaphase of mitosis? How

many DNA molecules are present in a chromosome of a cell at metaphase II of meiosis?

A chromosome in G1 of the cell cycle is composed of a very long molecule of double

stranded DNA. Recall that DNA is replicated during the S phase of the cell cycle. Thus

during metaphase of mitosis, each chromosome (i.e., each chromatid pair) will contain two

molecules of double stranded DNA (one molecule per sister chromatid). The following

diagram depicts the behavior of one homologous pair of chromosomes during mitosis. In a

real cell, chromosomes would not be visible during interphase of the cell cycle.

S phase mitosis telophase of mitosis

During prophase I and metaphase I of meiosis, a chromosome consists of a tetrad (4

chromatids or 4 DNA molecules) and is reduced to two chromatids (2 DN