13. Mendelian Genetics

X-Inactivation

X-Inactivation in mammals

 No. This would not explain the patched pattern. 

 No. This disorder results from a single gene. 

 No. Nondisjunction is a rare event and could not be responsible for multiple patches of skin with the abnormal phenotype. 

Heterozygous females are mosaic for traits that result from X-linked genes.

A genetic defect in humans results in the absence of sweat glands in the skin. Some men have this defect all over their bodies, but in women it is usually expressed in a peculiar way: A woman with this defect typically has small patches of skin with sweat glands and other patches without sweat glands. In women, the pattern of sweat-gland distribution can best be explained by __________.

X-Chromosome Inactivation and Escape Genes - Biological and Musical Analyses

HHMI BioInteractive: X Inactivation

Why Women Are Stripey

The XIST gene codes for an enzyme that methylates DNA on the X chromosome being inactivated.

No. Although DNA methylation is involved in the inactivation of an X chromosome, the product of the XIST gene is not composed of amino acids, so the gene product must be functional after transcription.

The XIST gene on the X chromosome that will remain active is expressed to produce multiple RNA molecules that bind to the X chromosome to be inactivated and effectively cover it up, thereby generating a Barr body.

No. The XIST gene that is activated and expressed is on the X chromosome to be inactivated.

Together with other proteins, the protein product of the XIST gene binds to histones and induces supercoiling of the DNA in one of the X chromosomes, thus inactivating it.

No. Although modification of the histone arrangement can contribute to X chromosomes inactivation, the product of the XIST gene is not a protein.

 The first and second listed responses are correct. 

 No. Only one of the listed responses is correct. 

The XIST gene on the X chromosome that will be inactivated is expressed to produce multiple RNA transcripts that bind to that chromosome and effectively cover it up, thereby generating a Barr body.

The gene product is not composed of amino acids.

Which of the following best describes the function of the XIST gene in X chromosome inactivation?

Secrets of the X chromosome - Robin Ball

X Inactivation and Epigenetics (2017) Etsuko Uno wehi.tv

In cats, fur color is determined by an X-linked gene; There are two alleles for this gene, one allele is for black fur and the other is for orange fur. In cats, a heterozygote female has calico (black and orange patches) colored fur. What kinds of offspring would you expect from the mating of a black female and an orange male?a) Calico females &amp; calico males.b) Black females &amp; orange males.c) Calico females &amp; black males.d) Orange females &amp; black males.

X Inactivation

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