Chromosomal abnormalities
- Created by: Former Member
- Created on: 04-04-11 16:38
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Chromosomal abnormalities
Sex chromosome abnormalities
- a significant cause of genetic disease
- chromosome abnormalities are found in 0.6% of live births, 50% of spontaneous abortions
Numerical chromosomal abnormalities
Polyploidy
- multiple sets of chromosomes (extra full set)
- triploidy (3n) and tetraploidy (4n)
- rare births, short lived
Aneuploidy
- the condition of having an abnormal number of chromosomes (not a multiple of haploid number)
- nullisomy - 2n - 2 (missing chromosome)
- monosomy - 2n - 1 (one missing copy of chromosome)
- trisomy - 2n + 1 (three copies of one chromosome)
Arises due to:
Non-disjunction
- failure of homologous chromosome (meiosis 1) or sister chromatids (meiosis 2) to separate at anaphase
Numerical sex chromosome abnormalities
Klienfelter syndrome
- 47, XXY karyotype (or more rarely 48, XXYY, 48 XXXY, 49 XXXXY), male
- form of trisomy
- 1 in 1000 male births
- common cause of male infertility
- tall stature
- mildly impaired IQ
- slightly feminised physique
- frontal baldness absent
- little chest hair
- some breast development
- testicular atrophy
- female type pubic hair pattern
- testosterone can improve secondary sexual characteristics
Turner syndrome
- XO, 45 X karyotype, female
- form of monosomy
- 1 in 5000 female births but >90% of cases are spontaneously aborted
- defects more prominent in puberty
- short stature
- characteristic facial features
- skin fold
- shield-shaped thorax
- constriction of aorta
- poor breast development
- widely spaced *******
- elbow deformity
- shortened metacarpals
- low hairline
- small fingernails
- rudimentary ovaries
- no menstruation
- brown spots
- mainly infertile
Autosomal abnormalities
- extra copy of chromosome
- all autosomal monosomies and most autosomal trisomies are lethal before birth
- only autosomal trisomies to survive to birth are Patau syndrome (chromosome 13) and Edwards syndrome (chromosome 18)
Down syndrome
- form of trisomy
- affects chromosome 21
- 15 in…
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