Question

You're studying a eukaryotic species with a haploid number of 7. The somatic cells in this species each contain a total of 1.8 billion base pairs of DNA, or approximately a total mass of 1.8 picograms (DNA weighs approximately 1 pg/ 1 Gbp)

a. You are observing cells of this species undergoing meiosis utilizing a special microscopy technique that allows you to estimate the mass of DNA in the nucleus. All of the cells you are currently observing are undergoing the same stage of meiosis, and you find the mass of DNA in the observed cells to be approximately 3.6 picograms. Based on this result, are these cells undergoing Meiosis I or Meiosis II, or have they completed Meiosis II? Explain your answer.

b. How many base pairs of DNA would be present in each of the cells from this species after Meiosis II is complete?

c. Draw the genetic material in a cell from this species undergoing Metaphase of Meiosis I. Indicate maternal and paternal chromosomes using different color or open/filled shapes.

d. Assuming genetic crossover does not occur in this species, what is the probability if you tested a single germ cell from an individual that it would only contain DNA originally inherited from its mother (maternal chromosomes)?

*This is all I was given on the question, there's no more info to add.

Answer 1

We should progress step by step.

A . A somatic eukaryotic cell with haploid no. 7 i.e n= 7, so, in somatic diploid cell (not germ line cell ) the total no. of chromosome 2n= 14, This 14 chromosome containing 1.8 billion base pare. So We know that Meiosis occures in germ line, where after completed meiosis II, each daughter cells contain half of the mother cells genetic material, that means in each germ cell, ( as in sperm or ovum), n=7.

Here the cells under observation is having the 3.6picograms of DNA mass which is exact 4 times on the germ cell.

In anyways this is not possible in normal meiosis unless there is some meiotic error with polyploidy.

as an example -

B.

If this sp. compleated meiosis 2 there would have haploid no. i.e. n= 7. But as each Chromosome having 2 Double stranded DNA double helix, in 2n mother cell have 14X 2 = 28 DNA double helix, after completed meiosis one, it would be 14 in each daughter cell, and after completed meiosis II it would be 7 in each daughter cell, i.e. exact 1/4th of the original mother cell. So there would be 0.45 billion base pairs of DNA would be present in each of the cells from this species after Meiosis II is complete.

C.

D. If there is no crossing over after Meiosis I there would each cell containts equal no. of maternal and paternal chromosome, then they are divided again in meiosis II, So out of 4 daughter cell, 2 can only have DNA from maternal origin. So, there is a 50% chance that we can get a single germ cell, only contain DNA originally inherited from its mother (maternal chromosomes).