Wk 6_Ch8.1-2_XY chromo biology

Wk 6_Ch8.1-2_XY chromo biology - LS 4 Wk 6 + 7 - Ch 8.1-5...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
LS 4 Wk 6 + 7 -- Ch 8.1-5 X/Y Chrom Biology, Human Karotype, Chrom Disorders Ch 8.1 Yilan Shi Dosage Compensation of X-Linked Genes Drosophila: males INCREASE X chromosome activity by acetylation/silencing DNA C. Elegans (???)- females decrease EACH X-chromosome activity by half. Mammals: X-chromosome is INACTIVATED randomly in early cell division o Chromosome condense at site: XIC o Makes “bend” in metaphase (of mitosis) visible o Chromosomes w/ deletions at this site = unactivated= cause prb’s o Xist = X-inactivation-specific transcript = only transcribed part of inactivated part of X chrom. not exon, it’s only a structure RNA (not protein after splicing, b/c splicing cuts off ORF) 2 Results of X-inactivatn 1. Female = mosaic for X-linked genes in somatic cells. B/c X-chrom inactivated randomly, ea body cell might have diff X turned off esp. if a F is heterozygous for an X-linked allele. 2. Dosage compensation for females equal copies of X-linked genes in M & F. Ex’s: Calico cat Marsupials= SELECTIVE X-inactivatn—Inactivate FATHER’s X Human female sweat glands Exceptions: Tips of arms not silenced – “ Telomeric region X + Y share homologous pairs of alleles CROSSOVER! Genes in “ Pseudoautosomal region ” (PARp) follow AUTOSOMAL inheritance pattern , but physically on X/Y 15% active genes on silent X active genes in lrg blocks in short arm tips Suggest farther away from Xist= more gene activity? PAR on tips of chromosomal arms !
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Activated genes on inactive X have transcription levels 15-50% explains why F hemop carriers = diff exprsn Evolution of Sex Chromosomes! X Y started as autosomes. When mammals + birds diverged (300-350mya), X + Y diverged
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/25/2010 for the course LIFE SCI 504675445 taught by Professor Dr.merriam during the Winter '09 term at UCLA.

Page1 / 7

Wk 6_Ch8.1-2_XY chromo biology - LS 4 Wk 6 + 7 - Ch 8.1-5...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online