Mutations and Genetic Analysis Flashcards
What are the different types of chromosomal abnormalities?
numerical
structural
mutational
What does trisomy mean?
instead of two pairs of chromosomes , three pairs of chromosomes in your cells
What system of abnormalities are responsible for 50% of trimester miscarriages?
trisomys
Describe Patau syndrome?
47, xx + 13
Describe Edwards syndrome?
47 xy + 18
Describe downs syndrome?
47 xx + 21
Describe klinefelter syndrome?
47 , XXY
What happens in normal meiosis?
cell duplicates the genomic material
then gets split into two daughter cells
then in meiosis 2, split what they have into 4 haploid cells
Describe non-disjunction?
the cell does not divide into daughter cells and then the one cell with duplicated material divides and have 2 complete cells and 2 empty.
and another way of non disjunction
successful meiosis 1 and duplicated material is successfully divided into daughter cells however in meiosis 2 one of daughter cells gets two of of chromatids instead of single.
What alleles are major contributor for trisomys?
maternal
What allele is the contributing factor for monosomy?
paternal as there should be a Y
What causes 95% of down syndrome?
Trisomy 21: non-dysjunction (95%), usually maternal origin
Unbalanced Robertsonian translocation (4%)
Mosaicism (1%)
What is trisomy 21?
Trisomy 21 (Down syndrome)
Incidence: 1 in 650 to 1 in 700
Increases with advancing maternal age
Characteristic facial dysmorphologies
IQ less than 50
Average life expectancy (50-60 years)
Alzheimer’s disease in later life
Chromosomal findings
Trisomy 21: non-dysjunction (95%), usually maternal origin
Unbalanced Robertsonian translocation (4%)
Mosaicism (1%)
What is trisomy 13?
Incidence: 1 in 5000
Multiple dysmorphic features and mental retardation
About 5% die within first month, very few survive beyond first year
Non-dysjunction (90%), maternal origin
Unbalanced Robertsonian translocation (10%)
What is trisomy 18?
Incidence: 1 in 3000
Severe developmental problems; most patients die within first year, many within first month
Non-disjunction (90%), maternal origin
What is Turner syndrome?
Incidence: 1 in 5000 to 1 in 10000 (liveborn)
Incidence at conception much greater, about 97% result in spontaneous loss
Females of short stature and infertile
Neck webbing and widely spaced nipples
Intelligence and lifespan is normal
What is Klinefelter syndrome?
Incidence: 1 in 1000
Tall stature, long limbs
Male but infertile, small testes, about 50% gynaecomastia
Mild learning difficulties
Give examples of structural abnormalities?
Balanced or unbalanced rearrangements
Translocations
Reciprocal: involving breaks in two chromosomes with formation of two new derivative chromosomes
Robertsonian: fusion of two acrocentric chromosomes
Deletions
Insertions
Inversions
What happens with unbalanced conditions in reciprocal translocations?
normal
balanced
one chromosome that has been unaffected and one that has been translocated. When this gets duplicated again, get an unaffected chromosome and one affected one.
Causing partial trisomy and partial monosomy.
One affected and one fine, when fertilised you have a partial monogamy and a partial trisomy.
Describe robertsonian translocation?
starts because of having two acrocentric chromosomes (p arm inactive)
q arms get joined together as one chromosome
What are the acrocentric chromosomes?
13 14 15 21 22
What are the different outcomes of a robertsonian translocation carrier?
refer to minutes 29;50
Describe chromosomal deletions?
breaks in chromosomes and part gets deleted out `
Describe inversions?
genetic material that is put into chromosome in one way but then through some mechanism-gets flipped around and genes now in diff position. Repressed, activated and changes outcome of gene transcription.
Describe genetic mutations?
level of DNA
disruptions of gene
SNP polymorphism- one nucleotide in a dna code gets changed
Describe coding mutations?
in coding regions
What are the different types of coding mutations?
silent -no effect
missense e.g. CGA to GGA and diff amino acid expressed
nonsense- stop codon where AA should be
shift-deletion/ insertion
How to name mutation of an adenine in position 1298 getting changed to guanine?
1298A>G
What does 1294del40 mean?
deletion of 40 base pairs
What does M252X mean?
instead of methionine on position 252, there’s a premature stop codon
What does Cys64Arg mean?
changed into argenine
What are the ways of detecting mutations?
polymerase chain reaction (PCR) - making more of DNA
gel electrophoresis
restriction fragment length polymorphism (RFLP)
amplification refractory mutation system (ARMS)
DNA sequencing
What do we need for PCR?
sequence information
oligonucleotide primers
DNA
Nucleotides
DNA Polymerase
How does PCR work?
split the DNA apart- denaturation at 93-95 degrees)
primer can anneal (50-70 degrees)
extending (70-75 degrees)
repeat 20-30 times
Describe gel electrophoresis?
separates DNA from PCR
fragments by size
apply an electric field
DNA is negatively
charged
separate through agarose gel matrix
visualise DNA fragments
SMALLER FRAGMENTS ON BOTTOM
Advantages of PCR?
speed
ease of use
sensitive
robust
Describe how restriction digest assay works?
have control samples that show what it should look like compared to test samples with mutations
What do restriction endonucleases do?
Degrade DNA of invading viruses
recognize specific DNA sequences
usually 4-8bp
always cuts DNA at same site
