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
What is another name for Trisomy 13?
Patau syndrome
What is the name of the sex chromosome aneuploidy 45 X?
Turner Syndrome
What is the name of the sex chromosome aneuploidy 47 XXY?
Kleinfelter Syndrome
Give some characteristics of Turner Syndrome.
Webbing of the neck Neck swelling at birth Short stature Streaked ovaries so INFERTILE No Barr Body of 1 X chr.
Give some characteristics of Kleinfelter Syndrome.
Testicular atrophy
Female distribution of hair
Infertility
Breast growth in males
What is a molar pregnancy?
When a triploidy occurs and the offspring gained 2 more copies of a whole genome. Incompatible with life and a mass of tissue, hair and teeth grows in the uterus that needs to be surgically removed.
There are two types of triploidy, what do they mean?
Digynic and Diandric?
Digynic- 2 sets of maternal chromosomes
Diandric- 2 sets of paternal chromosomes
What are reciprocal translocations?
When chromosomes are altered by the breakage and rejoining of chromosomes.
They are rearranged by breakage, recombination and random shuffling of similar sequences.
What are the effects of reciprocal translocations?
Can cause cancer in somatic cells or be silent
Or if it occurs in germline cells then a high chance of spontaneous abortion.
Two ways of reciprocal translocations
Alternate segregation results in?
Adjacent segregation results in?
Balanced chromosomes in gametes (no loss/gain which is okay)
Unbalanced chromosomes in gametes (lose/gain information in gametes)
Which chromosomes do Robertsonian translocations occur in?
Acroscentric chromosomes
Chr. 13, 14, 15, 21, 22
What are microdeletions?
Very large amounts of deletions around 5000 bp but you can’t see them under the microscope.
Give an example of a condition where large microdeletion in Chromosome 5 occur?
Cri Du chat syndrome
cry of infant sounds similar to a meow of a cat
Deletion in chromosome 5
Give an example of the condition with the microdeletion in chromosome 22?
DiGeorge’s Syndrome
What is the condition resulting from microdeletions in chromosome 15?
Angelman’s syndrome (deletion in maternal chr 15) and Prader willi (deletion in paternal chr 15)
Give some characteristics of Angelman’s syndrome.
Happy demeanor
lack of speech
balance difficulty
Give some characteristics of Prader Willi.
Overweight
narrow nasal bridge
thin upper lip
What are isochromosomes?
Fusion of chromosomes to get a chromosome with 2 p arms and a chromosome with 2 q arms
What are ring chromosomes?
Forms when a chromosome loses genetic material at the terminal portions and the ends fuse together to form a ring like structure.
Can be caused by harmful radiation exposure.
