3 The amount of DNA in an unfertilized egg nucleus of a cert

3. The amount of DNA in an unfertilized egg nucleus of a certain species is 9.0 picograms (9.0 x 10-12 g) . what would. be the DNA content, in picograms, in each of the following specific cells of this species?

a) A somatic cell in G1 stage of the cell cycle.

b) A spermatid

c) A secondary spermatocyte at very early Telophase II

d) Primary Oocyte at the Diplonema stage of prophase

e) Kidney Cell at Prophase..

f) Zygote at Anaphase of the First Cleavage Division…

g) Liver Cell in G2.

Solution

The amount of DNA in unfertilized egg is given like 9.0 pico grams. As it is unfertilized egg , it conatins only one set of chromosomes. It means female gamete has 9.0 pico grams, but we dont know the amount of DNA in male gametes. so let it be \'X\'

a) A somatic cell in G1 stage of the cell cylce:

In G1 phase the cell has two sets of DNA , one from female and one from male.So the total DNA content is 9.0+X pico grams.

b) A spermatid.

It will be \'X\'. Only single set of male gamete DNA

C) A secondary Spermatocyte at very early telophase II :

It will be X +X = 2X. Since at early stage of Telophase there are two sets of DNA in the spermatocyte.

d) Primary oocyte at the diplonema stage of prophase

It has 9.0+9.0 = 18 picograms . Because the primary oocyte will have two sets of DNA (2N). Hence the amount is double.

e) Kidney cell at Prophase

As it has vegetative cells , it has 2N amount of chromosomes , one from male and another from femlae. So it is 9.0 +X.

f) Zygote at Anaphase of the first cleavage division.

It contains 2N no of chromosomes. It is diploid. A zygote is a fertilized egg. so it contains one from father and one from mother. So it contains 9.0+X amount of DNA.

g) Liver cell in G2.

Liver cells are somatic and also during G phase , they have 2N chromosomes, they are diploid. So the amount DNA is 9.0+X. pico grams.

We know that in a species every individual will have almost 99% same amount and kind of DNA. So the X can be equal to 9.0 as females.

Then all the answers will be

a) A somatic cell in G1 stage of the cell cycle. = 9.0+9.0 = 18 pico grams

b) A spermatid = 9.0 pico grams

c) A secondary spermatocyte at very early Telophase II = 9.0 +9.0 = 18 pico grams

d) Primary Oocyte at the Diplonema stage of prophase = 9.0+9.0 = 18 pico grams

e) Kidney Cell at Prophase = 9.0+9.0 = 18 pico grams

f) Zygote at Anaphase of the First Cleavage Division = 9.0 +9.0 = 18 picograms

g) Liver Cell in G2. = 9.0+9.0 = 18 pico grams