Chromosomal Abnormalities Flashcards
(22 cards)
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 two chromosome abnormalities
Non homologous pairs
Unilateral information exchange
Can result in partial trisomy or monosomy
What are the types of chromosomal deletions
Deletion in microscope - cri-du-chat syndrome
Microdeletion - high resolution banding - 20+ genes deleted - DiGeorge syndrome
What is williams syndrome
Deletion of 7q11.23
Need to use flurescent in situ hybridisation to see
Aortic stenosis
Change in personality
Short upturned nose
Arched eyebrows
What is 7q11.23 syndrome
Delayed speech development
Autistic behaviours
Dilation of aorta
Flat eyebrows
(Duplicates normally have milder phenotype)
What are the classes of chromosomes
Robertsonian translocation
Occurs between acrocentric chromosomes
Homologous or non homologous
13 & 14, 14 & 15, 14 & 21
What is mosaicism
Two or more populations of cell with different genotypes
Non disjuncture during early development
Loss of extra chromosome in early development
Milder phenotype
