Dosage Compensation

Question 1

Dosage compensation

Answer 1

Dosage compensation is the crucial process that equalizes gene expression from the X chromosome between males (XY) and females (XX).

Question 2

Xist

Answer 2

mediates chromatin formation on the inactive-X Chromosome.

Question 3

roX

Answer 3

mediates chromatin formation on the hyper-active X Chromosome

Question 4

Gene switched on

Answer 4

• Active (open) chromatin
• Un-methylated cytosines (white circles)
• Acetylated histones

Question 5

Gene switched off

Answer 5

• Silent (condensed) chromatin
• Methylated cytosines (red circles)
• De-acetylated histone

Question 6

Nucleosome Remodeling Factor (NURF)

Answer 6

• NURF is an ATP-dependent chromatin remodeling complex that catalyzes nucleosome sliding in order to regulate gene transcription.
• It contains an ISWI ATPase, making it part of the ISWI family of chromatin remodeling complexes.
• NURF is highly conserved among eukaryotes and is involved in transcriptional regulation of developmental genes.
• The NURF complex in Drosophila contains four subunits: NURF301, NURF140, NURF55, and NURF38.

Question 7

X inactivation produced the coat pattern of a calico cat

Answer 7

Female clicks are heterozygous for the alleles O (orange) and o (black).

Inactivation of the O-bearing X chromosome produces a black patch expressing o, and inactivation of the o-bearing X chromosome produces an orange patch expressing O.

The white areas are caused by a separate genetic determinant present in calicos.

Question 8

Mechanisms of Dosage Compensation

Answer 8

1) Random inactivation of 1 X
2) Two-fold transcription of single X
3) Decreased transcription of both Xs by half

Question 9

Pseudoautosomal Regions And Dosage Compensation

Answer 9

The pseudoautosomal regions are required for sex chromosome segregation.

All pseudoautosomal genes escape X-inactivation.