Chromosomal abnormalities

Question 1

describe karyotyping

Answer 1

study of metaphase chromsomes
stain and pair up chromosomes
count number of chromosomes to check for duplication or deletions
check banding pattern

dark bands = G positive bands are AT rich and gene poor
light g negative bands are GC rich - gene rich

C banding - centromeres
q banding - fluorescence

Question 2

Describes some numerical chromosome abnormalities

Answer 2

polyploidy - gain of whole haploid set of chromosomes
aneuploidy - gain or loss of whole chromosomes
e.g. trisomy 21, trisomy 18 Edwards, Trisomy 13 Patau, monosomy 45 X - turners
mosaicism and x inactivation
uniparental disomy - presence of homologous chromosomes from 1 parent

Question 3

describe some structural chromosome abnormalities

Answer 3

reciprocal translocation - rearrangement by exchange of genetic material onto non homologous chromosomes
Robertsonian translocation - the rearrangement of genetic material by q arms of two acrocentric chromosomes combining to form a super chromosome and the loss of both p arms
deletions

Question 4

describe the use of FISH

Answer 4

used to identify deletions in chromosomes. especially for micro deletions as cannot see with karyotyping
can have centomere probes, whole chromosome probes or locus specific probes and can show fusions

Question 5

Give reasons for referral to karyotyping

Answer 5

infertility 
multiple miscarriages 
birth defects 
abnormal sexual development 
constitutional abnormalities 
prenatal diagnosis