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 & teroploidy?
Triploidy - extra set of chromosomes (total 69)
Tetraploidy - 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
Characteristics of Trisomy 18
Severe developmental abnormalities
Most die in first month or year of life
What is Turner syndrome?
45,X
Lack of a sex chromosome from father
What are characteristics of 45,X (turners syndrome)?
- Short stature & infertile
- 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 since all DNA is present.
What is an unblanced translocation?
Parents chromosome have undergone balanced translocation.
Can form gametes that lack 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?
2 long arms are fused and short ones lost
No genetic material is lost
What are the 2 types of deletion?
Terminal - DNA removed form chromosome end
Interstitial - DNA removed from inner part of chromosome
What are the 2 types of inversion?
Paracentric - Part of one arm is inverted
Pericentric - DNA on either side of 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?
Base changes but 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 STOP codon
How does a frameshift mutation occur?
Deletion or insertion shifts 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 DNA
Repeated many times to produce huge numbers of copies
What does Gel Electrophoresis do?
Separated DNA fragments by size through agarose gel matrix
Applying electric field to -ve DNA
Can visualise DNA.
What does ARMS stand for?
Amplification Refractory mutation system
What does RFLP stand or?
Restriction Fragment Length Polymerisation
How does RFLP work?
Certain Endonuclease always cut DNA at specific points in a chain of bases .
Uses Endonuclease then PCR to see length of cut section
Show if normal, mutant or heterozygous
Whats another name for Sanger DNA sequencing?
Chain Termination method
Why are dideoxynucleotides used in SANGER DNA sequencing?
Stop DNA polymersation reaction
Can analyse small section of DNA
How can the base sequence be determined in chain termination DNA sequencing?
Dideoxynucleotides dyed with fluorescent dye
Can See where bases joins
