chromosomal disorders Flashcards
human karyotype
chromosome analysis test evaluates the number and structure of a person’s chromosomes in order to detect abnormalities (gross screen of human genetic material)
- performed on any dividing cell
- screen test
define aneuploidy and how it is caused
chromosome number that is not a multiple of the normal haploid number (=23)
caused by non-disjunction during meiosis
trisomy
gain of 1 chromosome
monosomy
loss of 1 chromosome
down syndrome
- congenital condition
- chromosome 21 trisomy
- diagnostic test human karyotype
- increased incidence with increased paternal age
congenital vs acquired conditions
congenital are conditions existing at or before birth (germline)
mosaicism
somatic chromosomal abnormality occurring post-zygote formation, from non-disjunction
structural chromosome abnormalities
- reciporocal translocation
- robertsonian translocation
- inversion
- deletion
(can be noth constitutional and acquired)
reciprocal translocation
is a two-way exchange of material between two non-homologous chromosomes
constitutionally = normal phenotype due to no loss or gain of chromosome material
acquired = can result in an abnormal phenotype, as it brings together two genes normally far apart
how do carriers of reciprocal translocations present
- recurrent miscarriages
- chromosome examination of products of conception
- and more
inversion
a flip of chromosome material = structural rearrangement
involves two breaks on the same chromosome
- carriers usually phenotypically normal
deletion
loss of chromosomal material
- always results in a genetically unbalanced chromosome complement
terminal deletion
caused by a single break at the terminal region of chromosome and loss of that fragment
interstitial deletion
caused by two breaks in the same chromosome and loss of the intervening fragment
chromosomal tests
- karyotype analysis
- FISH (fluorescent in situ hybridization)
what are chromosomal tests used for
tests used to look at abnormalities in the number of chromosomes or big translocations and deletions of chromosomal material
when would karyotype analysis be carried out
suspected congenital disorders e.g. down syndrome or recurrent miscarriages
cancer / leukemia
- information helps with diagnosis and prognosis and even influence treatment given
differences between karyotype analysis and FISH
karyotype analysis requires dividing cells, whole genome scan
FISH = an adjacent to chromosome analysis looks at specific genes/parts of genes only
- don’t need dividing cells just any with a nucleus
- both congenital and acquired
