2002 Exam question

[Yacoubb]

Could someone explain the question on translocations and meiosis from the 2002 unit 4 vcaa exams. Q1.

Thanks!

[TrebleClef]

I also asked about this question, if you're asking about the sperm formation, and this is what SocialRhubarb replied


Okay, so we've got a male cat with a translocation producing sperm.

Normally in meiosis, homologous chromosomes are separated and end up in different cells after the first division. However, there is only one copy of chromosome 18, as one of the chromosomes has been translocated. This means that as the cell is undergoing its first meiotic division, spindle fibres can attach to one chromosome 18, and pull it to one side, but there is no other chromosome 9 for spindle fibres to attach t. This means that in the two cells produced by the first division, one cell has chromosome 18, but one cell does not.

Now we have one cell with a chromosome 18, and one cell without it, and the chromosome 9 will assort independently. So in the cell with chromosome 18, some will also contain a normal chromosome 9, and some will contain a translocated 9/18 chromosome. In the cell without chromosome 18, some will contain a normal chromosome 9, and some will contain a translocated 9/18 chromosome.

This leads to cells with a chromosome 9+18, a 9/18+18, a 9/18 by itself, and a 9 by itself.

EDIT:  Making the same assumption which t-rav mentioned - that the 9/18 chromosome will pair with the 9 chromosome, not the 18 chromosome.


Also, t-rav

It'll be because the 9 and the 9/18 are more likely to pair as homologous chromosomes during meiosis than the 9/18 and the 18. So it's very, very unlikely that they'd go together. Unless of course non-disjunction occurred.