Some XY individuals are phenotypically females. What chromosomal abnormality cou

Question

Some XY individuals are phenotypically females. What chromosomal abnormality could account for this?

Fragile X syndrome

Mitotic segregation

Dosage compensation

Mosaicism

A deletion of the portion of the Y chromosome containing the testis-determining factor

The leading cause of Turner syndrome is nondisjunction events. If Turner syndrome were only caused by nondisjunction of paternal origin, what other trisomic conditions would be expected to occur at least as frequently?

Down syndrome can be the result of a 14/21 Robertsonian translocation. Given that monosomy for chromosome 21 is lethal (as well as monosomy and trisomy for chromosome 14), what percentage of the viable offspring from translocation heterozygotes is expected to have Down syndrome and why?

Fragile X syndrome

Mitotic segregation

Dosage compensation

Mosaicism

A deletion of the portion of the Y chromosome containing the testis-determining factor

Explanation / Answer

Correct answer is "E": A deletion of the portion of the chromosome containing the testis-determinig factor.

In males, nondisjunction may leads to a sperm without having sex chromosomes which is the cause of Turner syndrome, can also lead to sperm carrying XY, XX or YY chromosomes that is depends on whether it is meiosis-I or meiosis-II. If it combined with a female X chromosomes, it can lead to get the XXY, XXX or XYY offspring.

the other possible trisomic condition may be Kleinfelter syndrome in which Nondisjunction in Meosis-I is responsible and it is more common in Meosis-I as compared to nondisjunction in Meiosis-II, and this Nondisjunction in Meosis-I leads to an XY sperm and the offspring contains XXY chromosomes.

Down syndromeis a chromosomal abnormality which is charaterised by the formation of extra copy of genetic material on chromosome 21. Translocation Down syndrome is mainly caused due to Robertsonian fusion between chromosome14 and chromosome 21. 50% of their gamates produce viable offspring. One out of three will have down syndrome, one out of three will be normal, one out of three will be a carrier.

Carriers of robertsonian translocation involving chromosome 21 (14;21), theoretically it will produce six types of gametes, in equal proportion andout of six, the two will be balanced. Other four gametes, two will be nullisomic for both chromosome 14 and 21, and two will be disomic for either of these chromosomes. The two-nullisomic gametes will direct to nonviable monosomy, on other hand the two disomic gametes will lead to trisomy for either chromosome 14 or 21. Because trisomy 14 is nonviable, only three of the gametes could develop into viable offspring, and the expected chance of Down syndrome is be approximately 1:3

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