Chromosomal Abnormalities Flashcards
What is trisomy?
extra copies of a chromosome
What is monosomy?
A diploid chromosome complement where one lacks its homologous partner
What is triploidy & heteroploidy?
Triploidy is the prescnene of an extra set of chromosmes (total 69)
Tetraploidy is the pressne of 2 extra sets of chromosomes (total 92)
How do numerical abnormalities mainly arise?
When chromosmes dont divide properly during meiosis (non-junction)
What is another name for trisomy 21?
Downs syndrome = Trisomy 21
What are characteristics of trisomy 21?
Maternal (chances increase with age) Distinc facial characteristics Alzhiemers in later life IQ < 50 50-60 yr life expectancy.
What is Trisomy 13 called?
Patau Syndrome = Trisomy 13
Characteristics of trisomy 13?
Mental retardation
Dysmorphic features
Maternal
Most die in 1st year
What is Trisomy 18 called?
Edwards Syndrome = Trisomy 18
What numerical abnormality causes severe developmental problems with most dying in the first month or year of life?
Trisomy 18 or Edwards syndrome
What is Turner syndrome?
45,X
A lack of a sex chromosome from the father.
What are characteristics of 45,X (turners syndrome)?
- Short stature & infetile
- All female
- Neck webbing & widely spaced nipples
- 97% die at conception
What is 47, XXY called?
Klinefelter Syndrome = 47,XXY
What are characteristics of Klinefelter syndrome?
- Tall & long limbed
- Infertile, small testes
- 50% develop breasts (gynaecomastia)
- Mild learning difficulties.
What is a balanced translocation?
Non-Homologous Chromosomes break and repair with some DNA swapped, usually fine because all DNA is present.
What is an unblanced translocation?
Parents chromosome have undergone a balanced translocation.
So they can form gametes that are lacking some material & have some duplicated
What kind of chromosoes are affected by robertsonian translocations?
Those with one long arm and one short containing no coding DNA. (Acrocentric)
How are two chromosmes fused in robertsonian translocation?
The 2 long arms are fused and the short ones lost, this way no gnentic material is lost.
What are the 2 types of deletion?
Terminal - DNA removed form the chromosme end
Interstitial - DNA removed from an innner part of the chromosome.
What are the 2 types of inversion?
Paracentric - Part of one arm is inverted
Pericentric - DNA on either side of the centromere is inverted (both arms change)
What is polymorphism?
Mutations in genes with no phenotypic effect
What are 4 sub-types of Coding mutations?
Silent
Missense
Nonsense
Frameshift
What is a silent coding mutation?
When a base changes but the amino acid is unchanged
What is a missense coding mutation?
One amino acid is changed to another
What is a nonsense coding mutation?
One amino acid is changed to a STOP codon.
How does a frameshift mutation occur?
Deletion or insertion shifts the whole chain along.
What does PCR stand for?
Polymerisation Chain Reaction
What are the 3 steps of PCR?
Denature, Anneal, Extend
What is the result of PCR?
Two copies of the DNA you started with.
Can be repeated many times to produce huge numbers of copies.
What does Gel Electrophoresis do?
Seperated DNA fragments by size through agarose gel matrix by applying an electric field to the -ve DNA so you can visualize the DNA.
What does ARMS stand for?
Amplification Refractory mutation system
What does RFLP stand or?
Restriction Fragment Length Polymerisation
How does RFLP work?
Certain Endonucleases always cut DNA at speciic points in a chain of bases .
So use an endonuclease then PCR to see the length of the cut section.
This will tell if its normal, mutant or heterozygous.
Whats another name for Sanger DNA sequencing?
Chain Termination method
Why are dideoxynucleotides used in SANGER DNA sequencing?
They stop a DNA polymersation reaction so you can analyse a small section of DNA
How can the base sequence be determined in chain termination dna sequencing?
The dideoxynucleotides are dyed with fluorescant dye so you can see which bases ones join where
