Question

meiosis modeling practice

1. use the cells shown below to fill in the alleles for the chromosomes in each cell at the end of meiosis i and meiosis i:

diagram of meiosis stages with cells

• how many cells are present at the end of meiosis i?
• are the cells haploid or diploid at the end of meiosis i?
• do the chromosomes contain replicated sister chromatids or individual single chromosomes at the end of meiosis i?
• how many cells are present at the end of meiosis ii?
• are the cells haploid or diploid at the end of meiosis ii?
• do the chromosomes contain replicated sister chromatids or individual single chromosomes at the end of meiosis ii?

Explanation:

Step1: Analyze end of meiosis I cell count

Meiosis I is the first division, where a single diploid cell divides into two cells. From the diagram, at the end of meiosis I, we can see two cells (the two middle - sized cells with "XX" - like structures). So the number of cells at the end of meiosis I is 2.

Step2: Determine ploidy at end of meiosis I

Meiosis I reduces the chromosome number by half. The starting cell is diploid (has two sets of chromosomes). After meiosis I, the cells have half the number of chromosome sets, so they are haploid? Wait, no. Wait, at the end of meiosis I, the cells are still in a state where chromosomes are replicated (sister chromatids are present). But in terms of ploidy, meiosis I results in two cells that are haploid? Wait, no, actually, at the end of meiosis I, the cells are haploid in terms of chromosome sets (n), but the chromosomes are still replicated (each chromosome has two sister chromatids). Wait, the definition: A diploid cell (2n) enters meiosis I. After meiosis I, the two daughter cells are haploid (n) but with replicated chromosomes (sister chromatids). So the cells at the end of meiosis I are haploid.

Step3: Chromosome structure at end of meiosis I

During meiosis I, the chromosomes are replicated before meiosis starts (in interphase). After meiosis I, the chromosomes in the daughter cells still have sister chromatids. So at the end of meiosis I, chromosomes contain replicated sister chromatids.

Step4: Analyze end of meiosis II cell count

Meiosis II is the second division, where each of the two cells from meiosis I divides into two. So 2 cells * 2 = 4 cells. From the diagram, at the end of meiosis II, we can see four cells (the four small cells with "I" - like structures). So the number of cells at the end of meiosis II is 4.

Step5: Determine ploidy at end of meiosis II

After meiosis II, the cells have the haploid number of chromosomes (n) and the chromosomes are no longer replicated (they are single chromosomes). So the cells at the end of meiosis II are haploid.

Step6: Chromosome structure at end of meiosis II

During meiosis II, the sister chromatids separate. So at the end of meiosis II, the chromosomes are individual single chromosomes (no sister chromatids attached).

Answer:

s:

• How many cells are present at the end of meiosis I? $\boldsymbol{2}$
• Are the cells haploid or diploid at the end of meiosis I? $\boldsymbol{\text{Haploid}}$
• Do the chromosomes contain replicated sister chromatids or individual single chromosomes at the end of meiosis I? $\boldsymbol{\text{Replicated sister chromatids}}$
• How many cells are present at the end of meiosis II? $\boldsymbol{4}$
• Are the cells haploid or diploid at the end of meiosis II? $\boldsymbol{\text{Haploid}}$
• Do the chromosomes contain replicated sister chromatids or individual single chromosomes at the end of meiosis II? $\boldsymbol{\text{Individual single chromosomes}}$