Know Why One X Chromosome Is On Silent Mode in Women

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When fertilization takes place, the sperm fertilizes the egg.
Now, sperms are of two types: Haploid-Y or Haploid-X,
whereas the egg is of just one type: Haploid-X.
So the resulting child may be Diploid-XY (Boy) or Diploid-XX (Girl).

However, in girls, the double dose of X chromosomes isn't really necessary, and one of the X chromosome is rendered inactive, by a process called Lyonization.

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Barr Bodies

Murray Barr discovered these inactive X Chromosome in a female somatic cell and named them Barr Bodies. They are sometimes referred to as sex chromatin.

The number of Barr bodies is one less than the number of X chromosomes.
Type Genotype Count of
Barr Bodies
Male XY 0
Female XX 1
Super Males XYY 0
Super Females XXX 2
Klinefelter's Syndrome XXY 1

Recessive Sex-Linked Genetics Disorders

The anomalies with genes found on X Chromosomes can lead to diseases like hemophilia, autism, Muscular dystrophy (Duchenne's pseudohypertrophy and Becker's benign pseudohypertrophic dystrophy, which is less severe), G-6-PD Deficiency syndrome, Color Blindness and Night Blindness.

Multiple Choice Questions

Which of the following statement is true?
(1) Length of X is more than that of Y
(2) X chromosomes is the sex determiner
(3) Length of X is equal to that of Y
(4) X chromosomes has Holandric genes

Ans: http://zoomgenetics.apphb.com/?id=m228

In female mammals the two X chromosomes are
(1) both active
(2) both inactive (silenced)
(3) one silenced
(4) both are partially active

Ans: http://zoomgenetics.apphb.com/?id=m234

Number of barr bodies in Super males?
(1) 0
(2) 1
(3) 2
(4) 3

Ans: http://zoomgenetics.apphb.com/?id=m270

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