bio question

[Dental2000]

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If nondisjunction of chromosome 21 occurs during meiosis I of spermatogenesis, which statement would be true about the resulting four sperm?

1)Two sperm would be normal.
2)Two sperm would lack chromosome 21.
3)Three sperm would lack chromosome 21.
4)All four sperm would lack chromosome 21.
5) One sperm would have an extra copy of chromosome 21.


any help is appreciated

 

[es1113]

should be 2)
the two sperm that didnt receive 21 would double in meiosis II without #21

 

[Demps]

if nondisjunction took place at meiosis I, that means that all tetrads went to one pole during the first anaphase instead of splitting 2n | 2n

so on the following meiosis II, you'd get n+1, n+1, 0, and 0. 0 just means nullsosomy. There is no chromosome at all. so in case for nondisjunction I, you have all 4 abnormal chromosome 2 that is one extra, 2 that has none. Hence, I believe answer is choice B.

On a side note, if nondisjunction II took place, then you have n, n, n+1, 0.
Therefore you would get two normal sperms and two that are abnormal.

Hope this helped!

 

[Dental2000]

if nondisjunction took place at meiosis I, that means that all tetrads went to one pole during the first anaphase instead of splitting 2n | 2n

so on the following meiosis II, you'd get n+1, n+1, 0, and 0. 0 just means nullsosomy. There is no chromosome at all. so in case for nondisjunction I, you have all 4 abnormal chromosome 2 that is one extra, 2 that has none. Hence, I believe answer is choice B.

On a side note, if nondisjunction II took place, then you have n, n, n+1, 0.
Therefore you would get two normal sperms and two that are abnormal.

Hope this helped!

U sir are great...Simple yet i was still getting confused..👍👍👍