1 / 7

Incomplete (unbalanced) chromosome sets: monosomy , trisomy , etc.

Complete chromosome sets: 1N , 2N, 3N, etc. Incomplete (unbalanced) chromosome sets: monosomy , trisomy , etc. Changes in chromosome number. Euploidy vs. aneuploidy. Autosomal trisomies and monosomies. Monosomy (2N - 1 ) … invariably fatal in humans.

fathia
Télécharger la présentation

Incomplete (unbalanced) chromosome sets: monosomy , trisomy , etc.

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Complete chromosome sets: 1N, 2N, 3N, etc. Incomplete (unbalanced) chromosome sets: monosomy, trisomy, etc. Changes in chromosome number Euploidy vs. aneuploidy

  2. Autosomal trisomies and monosomies Monosomy(2N - 1) … invariably fatal in humans Trisomy (2N + 1) … only three kinds tolerated in humans: # base pairs # genes # base pairs # genes Most common at birth—trisomy 21 (Down syndrome) 1 in 750 live births; 85% survive >1 year Less common Trisomy 18 (Edward syndrome, 1 in 10,000); <5% survive >1 year Trisomy 13 (Patau syndrome, 1 in 20,000); <5% survive >1year Why are trisomy 21, 18 & 13 tolerated better than other trisomies?

  3. sex chromosomal aneuploidy Sex chromosome aneuploidies are better tolerated than autosomalaneuploidies # base pairs # genes # base pairs # genes • XXY -- Klinefelter’s Syndrome • X0 -- Turner’s Syndrome • XXX -- Normal females • XYY -- Taller males, some mental retardation • Y0 -- Inviable Only one X-chromosome is active in males, females, and in individuals with an X-chromosomal aneuploidy XX XXY XXX XY Barr bodies

  4. X-chromosome inactivation • One X chromosome is packaged away. • Visible as a spot in female cells (Barr body). • The inactive X is randomly selected at about 32 cell stage of embryonic development. • In about half the cells, the maternal X is active; in the other half the paternal X is active. In some diseases involving genes on the X-chromosome this can yield a mosaic pattern of disease expression

  5. AnhidroticEctodermalDysplasia (caused by a mutation on the X chromosome)

  6. What’s unusual about this pedigree? XDXd XDY filled = colorblind X-linked recessive XDXd Xd=colorblind XD=color vision XdY -Identical twins with non-identical phenotypes -XDXd heterozygote is showing recessive phenotype X-inactivation phenotype… all-or-none (or in-between)?

  7. Meiosis II nondisjunction Meiosis I nondisjunction All 4 products defective 2 normal 2 defective How does aneuploidy arise? Major cause of aneuploidy—meiosis nondisjunction

More Related