Question

Drosophila melanogaster, the fruit fly, has a 2n chromosome number of 8. Assuming that a somatic G2 nucleus contains about 8.0 picograms of DNA, how many picograms of nuclear DNA would you expect in:

a) Mitotic metaphase
b) a primary oocyte (metaphase)
c) a secondary oocyte (metaphae)
d) a first polar body (metaphase)

Answer 1

During mitotic metaphase and primary oocyte metaphase in Drosophila, there are 8.0 picograms of DNA. In a secondary oocyte during metaphase and the first polar body, there are 4.0 picograms of DNA, as these cells are haploid postcompletion of meiosis I.

Step-by-step explanation:

In the context of Drosophila melanogaster, which has a diploid chromosome number of 8 (2n=8), and a somatic G2 nucleus containing about 8.0 picograms of DNA, we can determine the amount of DNA present at different stages of cell division. During the G2 phase, a cell has duplicated its DNA in preparation for mitosis, therefore, a G2 nucleus contains twice the amount of DNA compared to a G1 nucleus.

• (a) Mitotic metaphase: In mitotic metaphase, the cell contains 2 copies of each chromosome, just as it does during G2 phase, so you would expect to see 8.0 picograms of DNA, because the chromosomes are aligned and condensed but not yet separated.
• (b) Primary oocyte (metaphase): A primary oocyte in metaphase I of meiosis also contains 8.0 picograms as it is still diploid until the completion of meiosis I.
• (c) Secondary oocyte (metaphase): After the completion of meiosis I, a secondary oocyte is in meiosis II, and is already haploid, but since the chromosomes have not yet divided, it would contain 4.0 picograms of DNA, half of the amount in the primary oocyte before meiotic division.
• (d) First polar body (metaphase): The first polar body, being a byproduct of meiosis I, would similarly contain 4.0 picograms of DNA.

Answer 2

a) Mitotic metaphase

8 picograms

b) a primary oocyte (metaphase)

8 pecograms

c) a secondary oocyte (metaphae)

4 pecograms

d) a first polar body (metaphase)

4 pecograms

Step-by-step explanation:

a) In mitotic phase the chromosome numbers remains same as 8 because in this phase duplicated chromosomes align in center and separate to other poles. Therefore the amount of DNA will be 8 pecograms.

b) after the mitotic meta phase the cells divide into daughter cell with equal proportion of DNA which means each cell have 8 chromosomes. therefore they both contain 8 pecograms of DNA. The new daughter cells called as primary oocytes.

c) These primary oocytes (8 chromosomes) divides into two secondary oocyte each contain 4 chromosomes which means each cell have 4 pecograms of DNA.

d) Duplication of chromosomes occur in secondary oocyte and cell divides into polar body (4 chromosomes) and ovum (4 chromosomes). Therefore first polar body have 4 pecograms of DNA in it.

See the attachment for clarification.