Chromosome Biology 2 Flashcards
What types of chromosomal abnormalities can arise?
- Numerical
- Structural
- Mutational
What stages have the highest percentage incidence of abnormalities?
First trimester abnormalities - 50%
Children with mental retardation - 35-40%
Name two numerical abnormalities
- Trisomy (extra chromosome)
- Monosomy (loss of chromosome)
Name three trisomy conditions and the abnormality
- Patau: 47,XX+13
- Edwards: 47,XY+18
- Down: 47,XX+21
- Klinefelter: 47,XXY
Name a monosomy condition and the abnormality
Turner: 45,X
What does 46,XX+13 indicate?
- 46 chromosomes
- XX - the extra chromosome
- 13 - at which chromosome
What problems arise in non-disjunction?
- 1st stage: homologous pair not separated
- 2nd: sister chomatids fail to separate - one cell is disomy (2 copies)
What is an example of an autosomal aneuploidy syndrome?
-Trisomy 21 (down)
What does non-dysjunction cause?
Autosomal aneuploidy syndromes - Down, Patau, Edwards (only ones that survivable)
Examples of sex chromosomes aneuploidy syndromes?
- Turner
- Klinefelter
Examples of structural abnormalities
- Balanced/unbalanced rearrangements
- Translocations
- Deletions
- Insertions
- Inversions
Describe balanced translocations
Two non-homologous undergo reorganisation - retains same amount of DNA so no severe effects
Describe unbalanced translocations
Reorganistion leads to:
-Partial trisomy (extra chromosome)
-Partial monosomy (chromosome missing)
of each chromatid
Describe Robertsonian translocation
Translocation where two acrocentric chromosomes are fused but no DNA is lost
What happens in R translocation?
Two Q arms join, and two P arms join (usually lost)
-Unbalanced trans. leads to trisomy and monosomy
What is an acrocentric chromosome?
Centromere located near one end of the chromosome
Describe deletion mutations
Interstitial break in chromosome leading to deleted genetic material
Describe inversion mutations
Interstitial break in chromosome and inverted - no loss of DNA (balanced)
Name and describe the two types of inversion mutations
- Paracentric - on the arms
- Pericentric - around centromere
Examples of genetic mutations
- Germline or somatic
- Gene disruption
- Polymorphism
Types of genetic mutations
- Non coding
- Coding
Give examples of coding mutations
- Silent - no change to AA
- Missense - change of AA
- Nonsense - stop codon leading to truncated protein
- Frameshift -deletion/insertion
Cys64Arg
AA 64 changed from cys to arg
M252X
AA 252 codes sor stop codon
1294del40
At AA 1294 theres a deletion of 40 nucleotides
662-42C>T
42 nucleotides BEFORE 662 change from C to T
IVS2+12insG
12 nucleotides into exon theres an insertion of G
Methods of detecting mutations
- PCR
- Gel electrophoresis
- RFLP
- ARMS
- DNA sequencing
What is PCR used for
Amplifying small segments of DNA
What is required for PCR?
- Oligonucleotide primers
- DNA sample
- DNA polymerase (heat resistant)
What are the step in PCR?
- Denaturing: DNA heated into 2 strands (break H bonds)
- Annealing: temp lowered so DNA primer attached to template DNA
- Extending: temp increase and DNA polymerase enzyme forms new strand
What is the principle of gel electrophoresis?
Separating DNA fragments by size
Mechanism of gel electrophoresis
- Apply an electric field
- DNA negatively charged due to -ve phosphate backbone and so moves towards +ve electrode
- Separate through agarose gel matrix
- Visualise DNA fragments
PCR and gel electrophoresis
Gel used to visualised the results of PCR
PCR applications
- DNA cloning/sequencing
- Gene identification
- Mutation detection
What is the use of ARMs?
To differentiate between wild type (normal) and mutant alleles
Normal primer + wild type allele
Amplification
Normal primer + mutant allele
No amplification
Mutant primer + wild type allele
No amplification
Mutant primer + mutant allele
Amplification
What can ARMs be used in combination with?
PCR and Gel electrophoresis
What is a disadvantage of PCR?
Primer design is critical - need to know what mutation codes for condition
What are restriction endonucleases?
They’re enzymes from bacterial cell that degrade the DNA of invading viruses and recognise specific DNA sequences
What is RFLP analysis?
Use of restriction endonuclease to cut specific section of DNA and run through gel electrophoresis
What can RFLP analysis diagnose?
Sickle cell anaemia - use mutant primer in PCR to show mutant base
What is DNA sequencing?
Chain termination method using dideoxynucelotides - from 5’ to 3’ end
