It is a normal karyotype. Meiotic nondisjunction has occurred, there is an extra

Question

It is a normal karyotype.

Meiotic nondisjunction has occurred, there is an extra chromosome.

Meiotic nondisjunction has occurred, there is a missing chromosome.

There is a translocation.

A.

It is a normal karyotype.

B.

Meiotic nondisjunction has occurred, there is an extra chromosome.

C.

Meiotic nondisjunction has occurred, there is a missing chromosome.

D.

There is a translocation.

21 You have a newborn with severe congenital birth defects. You do a test? karyotype analysis and the result is above. What is your analysis of this

Explanation / Answer

B. Meiotic nondisjunction has occurred, there is an extra chromosome.

Humans have 23 pairs of chromosomes (normal karyotype), out of which 22 pairs are autosomes and 1 pair is sex chromosome. Males have one X and one Y sex chromosome and females have two X chromosomes.

From the given karyotype, it is cleared that the newborn is a female as karyotype contains two X chromosomes and Y chromosome is absent. But there is a trisomy of 18 chromosomes. In 18th chromosome, three copies are present (1 pair and an extra chromosome) instead of two copies. The newborn has Edwards syndrome which is caused due to the failure of sister chromatids to separate in the Anaphase stage of meiosis (meiotic nondisjuction) that leads to the unequal distribution of chromosomes in daughter cells.

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