Chromosomal Abnormalities Flashcards
How to prepare a karyotype
Collect venous blood Isolate white cell Culture to T-lymphocyte growth Add colchicine which arrest them in metaphase more recently prophase Place in hypotonic saline Fix and stained
What to chromosomes have in common
Centromere P arm (short arm) Q arm (long arm)
What does gisema staining do
Distinct bands
What do the colours mean in a karyotype
Different levels of compaction Dark (heterochromatin) compact fewer genes Light (euchromatin) open genes
Aneuploidy
Abnormal number of chromosomes
What is the purpose of meiosis
Random assortment and recombination Reduction from diploid to haploid
When does non disjunction occur
Uneven number of chromosomes in daughter cells Meiosis 1 all daughter cells affected Meiosis 2 half affected
Why is sex chromosome aneuploidy tolerated
X inactivation Low gene content on Y chromosome
What is the pseudo-autosomal region
X region on the X gene which has not been activated is activated
What is Trisomy 21
Down syndrome 3 copies of 21
Why is there a maternal age effect
Egg is stuck of meiosis for a long time Degradation of factors which hold homologous chromatids together
Why is there a paternal age effect
Under 23 mitotic division Age is not a risk factor Smoking is a risk factor (not maternal)
What is the standard nomenclature
Where does crossover occur
Prophase 1
Increase genetic diversity
Chiasma
What are single chromosome abnormalities
Deletion of parts
Duplication - unequal crossover
Inversions - near centromere
What are the classes of chromosomes
