5. Answer the following questions regarding X-inactivation 46,XX a. What are XIS

Question

5. Answer the following questions regarding X-inactivation 46,XX a. What are XIST and TISX? (1 pt) 46,XY -47,XXY 49,XXXXY Figure 2 Expression ofl the X0ST gene in males, Semalies and somatic cell hybrids b. The image to the right is a gel blot of RNA from cells with different chromosomal make-ups. The spots indicate the amount of XIST in each of the cells. Explain why there is more XIST produced in some cells based on their chromosomal composition. (1 pt) 6. A DNA fragment with the following base sequence has some cytosine bases that are methylated (indicated by C') and others that are unmethylated. To determine the location of methylated and unmethylated cytosines, researchers sequenced this fragment both with and without treatment with sodium bisulfite. Give the sequence of bases that will be read with and without bisulfite treatment. (1 pt) ATCGC GTTAC ATTGC ATCA

Explanation / Answer

1. XIST = X inactive specific transcript.

It is a non-coding gene located on the X-chromosome. Its transcript is involved in the inactivation of extra copies of X-chromosomes.

TSIX is a complementary non-coding RNA anti-sense to XIST RNA. It binds to XIST during X-chromosome inactivation.

2. The amount of XIST produced depends upon the number of additional X-chromosomes present in an organism.

46 XX = 1 additional X-chromosome

46 XY = 0 additional X-chromosome

47 XXY = 1 additional X-chromosome

49 XXXXXX = 4 additional X-chromosomes

46 XXXXY = 3 additional X-chromosome

3. Bisulfite treatment converts cytosine to Uracil.

5-methylcytosine can not be converted to Uracil.

So,

Sequence without bisulfite treatment = ATCGCGTTACATTGCATCA

Sequence with bisulfite treatment = ATUGCGTTACATTGCATUA

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