Question

Consider an animal cell that has eight chromosomes (four pairs of homologous chromosomes) in G₂ phase. Match how many of each of the following features the cell will have at mitotic prophase :

A. sister chromatids

B.        centromeres

C.        kinetochores

D.        centrosomes

E.         centrioles

Answer 1

Ans: The cell cycle comprises of G1 phase in which growth is taking place, S phase which is synthesis phase in which replication of DNA taking place followed by G2 phase which is a preparatory phase for mitosis and the last one M phase in which cell divison takes place.

The M phase comprises of Prophase, Metaphase, Anaphase and Telophase and lastly Cytokinesis.

Now as given in the question that at G2 phase an animal celll has 8 chromosomes and we have to find features at prophase.

A) At prophase each chromosome is comprises of a pair of sister chromatids so in this animal cell we have 16 sister chromatids at prophase.

B) These sister chromatids are held together by centromeres so which means that each chromosome has a single centromere so this animal cell has 8 centromeres.

C) Kinetochores start, control, and supervise the striking movements of chromosomes during cell division. During mitosis, which occurs after chromosomes are duplicated in S phase, two sister chromatids are held together by a centromere. Each chromatid has its own kinetochore, which face in opposite directions and attach to opposite poles of the mitotic spindle apparatus. From this we can say that as each chromosome has 2 sister chromatids so each chromosome has 2 kinetochore and we have total 8 chromosomes whch means we have 16 kinetochore at prophase.

D) The centrosome is an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell, as well as a regulator of cell-cycle progression.Centrosomes are composed of two centrioles arranged at right-angles to each other, and surrounded by an amorphous mass of protein termed the pericentriolar material (PCM). This means that the pair of centrioles combinally make a single centrosome which means that each cell contains a single centrosome. So the animal cell also contains only a single centrosome.

E) Since the single centrosome comprises of 2 centrioles arranged at righ angles to each other we can conclude that at prophase the cell has a pair of centrioles.