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Which of the following is FALSE regarding X-Chromosome inactivation.

a. In female mammals, one of the two X chromosomes is highly compacted and transcriptionally inactive
b. Calico fur coloration is due to inactivation of X chromosomes in heterozygous female cats
c. Inactivated X chromosome is called a Barr body
d. Inactivated X chromosome happens in the Zygote
e. X-Chromosome inactivation is Random (either the maternal or paternal chromosome)

1 Answer

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Final answer:

The false statement about X-Chromosome inactivation is that it occurs in the zygote. It actually occurs early in embryonic development, not at the zygote stage, with the future somatic cells of the embryo inactivating one X chromosome, which becomes a Barr body.

Step-by-step explanation:

The statement that is FALSE regarding X-Chromosome inactivation is 'd. Inactivated X chromosome happens in the Zygote'. X-Chromosome inactivation occurs early in development when the female mammalian embryo consists of just a few thousand cells, not at the zygote stage. Each cell in the embryo will inactivate one of its two X chromosomes by condensing it into a structure called a Barr body. This process is random, meaning either the maternal or paternal X chromosome can be inactivated, but once inactivated, all cells derived from that one will have the same inactive X chromosome. This process is crucial for females to compensate for their double genetic dose of the X chromosome. In calico or tortoiseshell cats, the variegation of coat color is due to X inactivation of different X chromosomes having different alleles for the coat color gene in different cells during embryonic development.

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