Nondisjunction during Meiosis II (DAT Bootcamp)

[veryhappylabrador]

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From DAT Bootcamp: "Nondisjunction occurring during meiosis II, followed by fertilization, would result in a zygote with which of the following chromosomal descriptions?"

I thought it would be triploid, but the answer is aneuploid.

Nondisjunction at Meiosis II would give rise to one cell with 23 chromosomes (but 46 chromatids). If it were fertilized by a haploid gamete, wouldn't it contain 69 chromosomes and be 3n? I thought aneuploid only referred to an abnormality such as containing an extra chromosome or two, not an entire set of chromosomes.

Thank you.

 

[veryhappylabrador]

From DAT Bootcamp: "Nondisjunction occurring during meiosis II, followed by fertilization, would result in a zygote with which of the following chromosomal descriptions?"

I thought it would be triploid, but the answer is aneuploid.

Nondisjunction at Meiosis II would give rise to one cell with 23 chromosomes (but 46 chromatids). If it were fertilized by a haploid gamete, wouldn't it contain 69 chromosomes and be 3n? I thought aneuploid only referred to an abnormality such as containing an extra chromosome or two, not an entire set of chromosomes.

Thank you.

Wait...it has 46 chromatids but still has 23 chromosomes. Therefore it still has 46 chromosomes upon fertilization, therefore it isn't 3n, it is still 2n but has extra chromatids. I think that is the correct explanation.