Cytogenetics Flashcards
What is the human Karyotype?
46 chromosomes
22 pairs of autosomal chromosomes and 2 sex chromosomes.
What is a Monosomy/Trisomy? AKA ANEUPLOIDY
Loss or gain of a chromosome/multiple chromosomes
What is monoploidy/polyploidy? AKA EUPLOIDY
Loss or gain of a whole genome
What does karyotype mean?
a detailed description of the chromosomal content of an organism including number, features and banding pattern of chromosomes.
What are the steps of Karyotype analysis?
1) Take blood
2) Add culture medium and mitogen
3) Culture at 37 degrees for 3 days
4) Add hypotonic saline
5) Fix cells so proteins drop out
6) Drop cells ontp slide
7) Digest cells with trypsin and Giemsa stain
8) Analyse the metaphase spread using adobe
How do we get darker bands using Giemsa stain?
Those areas in the DNA re A and T rich.
What is the size of the chromosomes going from 1 to 22?
Longest is chr 1 to shortest chr 22
What is meant by chromosomes being metacentric, submetacentric, acrocentric and telocentric?
The centromere is near the middle,to one side, near one end, at the very end.
What is an ideogram?
An ideal picture of what the ideal human karyotype should look like.
What do we use to distinguish between similar looking chromosomes?
Banding pattern and centromeric index.
When during the cell cycle can we see chromosomes?
Metaphase Less compaction (in middle of metaphase) means better resolution and we can see more banding pattern
What is a pair of chromosomes (1 from mum and 1 from dad) known as?
Homolygous pair of chromosomes.
What does this nomenclature code mean?
46, XY,del(1)(p21)
47, (+XXY)
46, XX, t(2;4)(p12;q13)
Normal male karyotype except there is a deletion in chromosome 1 on the short arm in band 2 sub band 1
Trisomy with the addition of an extra X chromosome
Normal female karyotype except there is a translocation between chr 2 (from short arm band 1 sub band 2) to chr 4 (long arm band 1 sub band 3)
What is FISH?
Flourescent in situ hybridization
Use flourescent locus specific probes to analyse chromosomes and identify genetic disorders
What is the main advantage of FISH?
The cell does not have to be in metaphase to visualise the chromosomes and can be automated using computer analysers.
This saves time and doesn’t require 3 year trained professionals
What is Cot-1 DNA?
mops up any repetitive sequences and prevents them binding to other sequences to remove an overall glow that interferes with flourescent analysis.
What is Array Comparative Genome Hybridisation?
Comparing normal genome to patient genome using flourescent probes.
CGH is a molecular cytogenetic technique that allows detection of DNA sequence copy number changes throughout the genome in a single hybridisation.
What does it mean in an array CHG if there is more green than red? more red than green?
duplication or gain of chromosomes
Deletion or loss of chromosomes
What is the basic methodology of a CGH?
1) Isolate DNA from 2 different cell types or individuals
2) Label DNA with 2 different flourescent dyes
3) Compare the labelled DNA with normal set of chromosomes.
How does aneuploidy occur as a result of non-dysjunction in meiosis?
Sister chromatids don’t separate during anaphase, one cell gets 2 chr and the other cell gets none.
What is another name for Trisomy 21?
Down Syndrome
Give some characteristics of down syndrome.
Mental retardation
Depressed nasal bridge
Epicanthal fold
Single palmar crease
What is another name for Trisomy 18?
Edward Syndrome
Give some characteristics of edward syndrome.
Clenched fist
Rocker bottom feet
Low set ears
Small lower jaw
