Question

Consider an animal cell that has 8 chromosomes (4 pairs of homologous chromosomes) in G1 phase. How many of each of the following structures will the cell have at mitotic prophase?

1. sister chromatids
2. centromeres
3. kinetochores
4. centrosomes
5. centrioles

a. 2
b. 4
c. 8
d. 16

Answer 1

At mitotic prophase, an animal cell that began with 8 chromosomes in G1 phase will have 16 sister chromatids, 8 centromeres, 16 kinetochores, 2 centrosomes, and 4 centrioles.

Step-by-step explanation:

A student asked how many of each of the following structures - sister chromatids, centromeres, kinetochores, centrosomes, and centrioles - will an animal cell have at mitotic prophase if it begins with 8 chromosomes (4 pairs) in G1 phase.

During the S phase of interphase, each chromosome is replicated, leading to the formation of two sister chromatids held together at a centromere. Thus, at the onset of mitotic prophase, a cell that started with 8 chromosomes will now have:

1. 16 sister chromatids (8 chromosomes × 2)
2. 8 centromeres (one per pair of chromatids)
3. 16 kinetochores (one per chromatid)
4. 2 centrosomes (as each replicated during S phase)
5. 4 centrioles (each centrosome has a pair)

This is because chromosomes duplicate during the S phase, and structures like centrosomes and centrioles are also duplicated in preparation for cell division.