A large family has a history of multiple aneuploid diseases such as Down Syndrom

Question

A large family has a history of multiple aneuploid diseases such as Down Syndrome, trisomy-18 and Klinefelter Syndrome (XXY). The propensity to defects seems to be inherited, but the gene responsible is unknown.
What types of candidate genes would be most likely to lead to aneuploidy if they were mutated?

A. Genes that are part of the G1 checkpoint of mitosis.

B. Genes that encode proteins involved in chiasma formation.

C. Histone genes.

D. Genes that control DNA synthesis.

I have already answered and I know it is not A or D. Just need clarification.

Explanation / Answer

answer would be (B). Genes that encode proteins involved in chiasma formation

Down Syndrome - aneuploidy caused by nondisjunction.
Klinfelter Syndrome - nondisjunction in sex chromosomes that results the male to have two X chromosome (XXY)

Non disjunction of chromosomes results due to:

- during anaphase II, sister chromatids fails to separate properly  
- during anaphase I, homologous chromosomes fails to separate properly  
- during meiosis II, centromeres fails to split apart properly  

individual has an exact multiple of the haploid number of a chromosome number, like sex trisomy 47, XXY or trisomy 21, aneuploidy is due to nondisjunction during meiosis that is the chromatids fail to move to opposite poles during anaphase.

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