Nondisjunction

[deleted647690]

There was a question in BR about which diagram shows secondary nondisjunction in spermatogenesis. When you draw out a chart showing nondisjunction, why does it seem like it is always assumed that the nondisjunction only occurs in one set of cells? For example,

When I saw the question describing nondisjunction, I assumed it meant that all 4 daughter cells experienced the effect. However, the answer was just like the diagram above, where one gamete still turned out normally. Why does nondisjunction only occur on the one side?

---

Members don't see this ad.

 

[theonlytycrane]

Non-disjunction is the failure of chromosomes to separate during cell division. This isn't supposed to happen, so it's more rare when it does happen. It depends on the question that you saw, though. Above, if the gamete with red chromosomes undergoes non-disjunction, this wouldn't have an influence on the cell division of the gamete with yellow chromosomes.

 

[deleted647690]

Non-disjunction is the failure of chromosomes to separate during cell division. This isn't supposed to happen, so it's more rare when it does happen. It depends on the question that you saw, though. Above, if the gamete with red chromosomes undergoes non-disjunction, this wouldn't have an influence on the cell division of the gamete with yellow chromosomes.

I think the question just said to pick the diagram that showed the results of secondary nondisjunction. I thought that would mean that both red and yellow chromosomes in the diagram above fail to divide; however, for some reason, nondisjunction only occurs in one set (the red ones) and the yellow ones turn out normal. Is this always the case? Nondisjunction does not occur in both sets?

It didn't specify that disjunction should only occur in one pair in the question, it just said something general like "secondary nondisjunction"

 

[theonlytycrane]

It can, but the non-disjunction event for each cell in meiosis II would be independent. Since it's more rare than normal division, it would be more likely that only one cell would show failure of chromosome separation.

 

[deleted647690]

It can, but the non-disjunction event for each cell in meiosis II would be independent. Since it's more rare than normal division, it would be more likely that only one cell would show failure of chromosome separation.

Thanks