Question

A certain organism has diploid number of chromosomes 2n = 4. Show the following two cases:

- metaphase of mitosis, where the organism is trisomic for the 2nd chromosome (2n+1 = 5)

- metaphase of meiosis I, without any abnormalities

Note:

Feel free to 'write' chromosomes using X, for example like this (no need to draw the cell or draw spindle fibers):

Metaphase:

XX

XX

XX

XX

XX

Answer 1

Metaphase is the stage in which the chromosomes align in order to get segregated.

- metaphase of mitosis, where the organism is trisomic for the 2nd chromosome (2n+1 = 5)

We are going to draw the chromosomes aligned in the center, remember that the units being segregated are the chromatides, so the chromosomes will look like this:

Note there are 5 chromosomes, due to the trisomy.

- metaphase of meiosis I, without any abnormalities

Remember that meiosis has its differences compared to mitosis, one of those differences is that not only the sister chromatides get segregated, but the homologous chromosomes too. In metaphase I the homologous get segregated, and the sister chromatides segregate until metaphase II. So in this case the drawing looks like this:

There are 4 chromosomes in pairs, they are arranged with their homologous.