Handout 6 (for student)

Handout 6 (for student) - Duyen-Anh Pham BICD 100...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Duyen-Anh Pham BICD 100 [email protected] HANDOUT #6 Dosage Compensation: The fact that females have an extra copy of the X chromosome introduces a problem: If females have twice as many X-linked genes, then they should produce twice as many proteins that are encoded by these genes? Thus we can say that females have an extra “dose” of the X chromosome. The mechanism developed in humans to compensate for this extra dose is called Dosage Compensation. The purpose is to balance the dose of X chromosome gene Dosage compensation occurs in Drosophila, C. elegans, and Mammals by different mechanisms. In Mammals, the extra dose of the X chromosome is compensated for by inactivating it. So females have only 1 active X chromosome. The X chromosome is inactivated by condensing it to the form of heterochromatin. The inactivated chromosome is called a Barr Body. N-1 rule: females Turner 45, X with no Barr body Males Klinefelter 47, XXY with 1 Barr body (still forming hypothesis to explain why males having inactivated X chromosome) Lyon Hypothesis : which X chromosome is inactivated, from paternal origin or from maternal origin? Answer: occurs randomly in somatic cells during early development. e.g. red-green color blindness is X-linked recessive disorder. Color blindness males are hemizygous (X &Y) therefore fully color-blind in all retinal cells. Heterozygous females display mosaic retinas, patches of defective color perception surrounded by normal color perception.
Background image of page 1

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

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/28/2009 for the course BICD BICD100 taught by Professor Smith during the Winter '09 term at UCSD.

Page1 / 3

Handout 6 (for student) - Duyen-Anh Pham BICD 100...

This preview shows document pages 1 - 2. Sign up to view the full document.

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