How can whole chromosomes can be lost or added during meiosisexplain?

Answer 1

During anaphase II of meiosis, the chromosomes are being pulled apart. If the spindle fibers aren't wholely attached to the centromere (at the center of the chromosomes) they might not separate evenly, resulting in monosomy or, inversely, trisomy. This renders gametes with extra or missing chromosomes, leading to illnesses like down's syndrome (Down's is trisomey of the 21st chromosome. There are three of them as opposed to 2, hense TRIsomey).

Sorry there's no drawing application, but I'll do my best to make you a diagram.

Here is the diploid cell before mieosis I.

11 22 33

Here it is after DNA synthysis

1111 2222 3333

And after telephase I

11 22 33 11 22 33

There are now 2 diploid cells. Gametes (sperm and eggs) are haploid, so the cell divides one more time without performing synthysis.

1 2 3 1 2 3 1 2 3 1 2 3

That is what occurs under normal conditions.

When something messes up...

after synthysis

1111 2222 3333

After Telophase 1

11 22 33 11 22 33

After telephase 2

11 2 3 2 3 1 2 3 1 2 3

That is an example of non-disjunction in meiosis II

The result of non-disjunction in meiosis I...

After Synthysis

1111 2222 3333

After telophase I

1111 22 33 22 33

After telophase II

11 2 3 11 2 3 2 3 2 3

Evidently, this is going to cause some problems. :)