Unit 3 -Chromosomal Abnormalities Flashcards
describe a sub-metacentric chromoome and give examples
short (p) arm
long (q) arm
- examples: chromosomes 6-12, X
what is a metacentric chromosome?
centromere is in middle - e.g. chromosome 1
what is an acrocentric chromosome?
very short (p) arm which can be deleted without harm - examples: 14, 21, Y
when genes are being labelled, in what order are the autosomes?
of decreasing size
what are the chromosomes stained with?
giemsa
how are genes labelled?
chromsome number, arm (either p or q), position on arm (main band and sub types)
what is the difference between a karyogram and karyotype?
karyogram - depiction (image) of chromosome set
karyotype - description of chromosome set
how is a karyotype recorded?
number of chromosomes, identity of sex chromosomes and anomalies
what are the karyotypes of normal male and female?
Male: 46, XY
Female: 46, XX
what is aneuploidy? how does it arise?
presence of extra individual chromosomes or absence of chromosomes
arises from non-disjunction during meiosis - leads to disomic gametes (two copies) and nullisomic gametes (no copy)
- when gametes fertilise, it will have three copies= trisomy or 1 copy = monosomy
what is the karyotype for a female with down’s syndrome?
47, XX, +21
what is the karyotype of a triploid male?
69, XXY
male has polyploidy - extra set of chromosomes
what is the karyotype of a female with turner’s syndrome? state the consequences of this sex chromosome aneuploidy
45, X
short stature,infertility - incomplete ovarian development
what is the karyotype of a male with Klinefelter’s syndrome?
47, XXY - extra X chromosome - infertility, small testicles
why are the effect of sex chromosomes aneuploidies so mild?
X chromosome activation ensures balance in number of X-chromosome between males and females so only 1 X chromosome is active
what type of structural abnormality is Cri du Chat syndrome? give karyotope of male wih this condition
deletion of short arm of chromsome 5 - development delay, cognitive impairment
46, XY, del(5p)
what is a reciprocal translocation?
exchange of material between non-homologous chromosomes
what is a robertsonian translocation? - give consequences
fusion between long arms of acrocentric chromosomes with loss of short arms
- risk loss/ gain of materials in gametes
- if occurs between two copies of chromosome 21 -all offspring will have down’s syndrome
what are the two forms of prenatal diagnosis of common aneuploidies?
non-invasive - biochemical markers in circulation + ultrasound - produces false positives (1:9)
invasive - amniocentesis (small amount of amniotic fluid retrieved) and chromosomal analysis - definitive result
what is the “philadelphia” chromosome?
reciprocal translocation between chromosome 9 and 22 = common in myeloid leukaemia (bone cancer)
- produces fusion gene = BCR-ABL - codes for tyrosine kinase- abnormal cell proliferation
