Question

- (4 pt) The cell to the left is undergoing: A. Mitosis B. Meiosis I C. Meiosis II Ito yo) If there is a cross over between genes A and B, and E and G, what is the arrangement of genes on the gametes after meiosis II? Make a simple drawing of this below on the figure. (4 pt)

Answer 1

The given parental cell has 2n = 4 chromosomes. After undergoing cell division, daughter cells have n = 2 chromosomes. We know that, after undergoing meiosis chromosome number in each daughter cell is reduced by half, which is the case here. Thus, the cell undergoing meiosis. So, we can ignore option A (mitosis). Now, we have to find if the cell is undergoing meiosis I or meiosis II. We noticed that parental cell is yet to complete reduction division, in which chromosome number is halved. Thus, the cell is undergoing meiosis I. So, correct answer will be option B.

Note: Assuming that loci of black chromosome are Abc (Top left-hand side) & yellow chromosome are aBC (Top right-hand side). We also assume that there is no mistake in the allele notation in the bottom two chromosome as both contain g allele instead of one G & one g allele.

Parts of the non-sister chromatids are exchanged during crossing-over. According to the question, a single cross-over occurs between genes A & B & between E & G. Thus, we will get two parental gametes & two recombinant gametes. Thus, parental gametes for chromosomes containing ABC loci will be Abc & aBC; recombinant gametes of these chromosomes will be ABC & abc. In case of bottom two chromosomes, as both chromosomes contain g allele, a cross-over between E & G locus will not change the final gamete product; however, their combination will change. Arrangement of genes after meiosis II is shown in below image.

Parental Cell (2n = 4) lou wor After meiosis II Daughter cells (n = 2)