genetics Flashcards
how do we analyse DNA?
lots of base pairs -> aCGH - for deletions/duplications
(chromosome/karyotype analysis for balanced rearrangements)
little BP - polymerase chain reaction (PCR) + Sanger sequencing or Next generation sequencing
focused testing - PCR
allows selection of one small piece of humans genome + amplify it
-> make lots of copies of one short stretch of genome
promotor + splice site sequence changes effect
stop transcription or cause abormal splicing
effect of base change causing an amino acid change
change in protein sequence
- not every base change causes disease
may or may not reduce protein function
some missense mutations make protein work faster
penetrance
the likelihood of having a disease if you have a gene mutation
100% penetrance = you will always get the disease if you have the mutation
mendelian disorders
segregates in families
- a disease that is predominantly caused by a change in a single gene (high penetrance)
autosomal dominant, recessive, X-linked
high penetrance, small environmental contribution
risk of female carrier’s kids being affected in Xlinked recessive inheritance
half her male children will be affected
half of female children will be carriers
risk of affected male’s kids being affected in xlinked recessive inheritance?
all of male kids will be normal -> NO MALE TO MALE TRANSMISSION
all female kid will be carriers
mendelian vs multifactorial
mendelian = high penetrance, small environmental contribution
multifactorial - genetic change is just another risk factor, penetrance for ant one mutation is low
shared genes in mono- v dizygotic twins
mono - share all their genes
di - share 50% of their genes
DNA replication happens during what phase of the cell cycle
S phase
DNA can be damage during replication
repair mechanisms exist - defect in these can cause disease
mitosis
one diploid parent
2 identical diploid daughter cells
meiosis
One diploid parent cell becomes 4 haploid daughter cells
o One of each chromosome to each cell
- Crossing over occurs – genes segregate independently, even if on the same chromosome
- Occurs in gamete formation
Ribonucleic acid (RNA)
- Single stranded
- Ribose in backbone not deoxyribose
- Uracil instead of thymine
amount of protein produced is determined by..
- Rate of transcription – manufacture of pre-mRNA
- Rate of splicing to mRNA
- Half life of mRNA
- Rate of processing of polypeptide
polymorphisms
- any variation in the human genome that has a population frequency of more than 1%
- OR
- Variation in human genome that does not cause disease in its own right
o May however predispose a common disease
mutation
- A gene change that causes genetic disorder
OR - Any heritable change in human genome
chromosome changes that cause disease - balanced vs unbalanced chromosome rearrangement
Balanced chromosome rearrangement
o All the chromosomal material is present
Unbalance chromosome rearrangement
o Extra or missing chromosomal material
o Usually 1 or 3 copies of some of the genome
–>(developmentally bad news)
Unbalanced rearrangements = multiple malformations or miscarriage
aneuploidy
whole extra or missing chromosome
robertsonian translocation
2 acrocentric chromosomes stuck end to end
increased risk of trisomy in pregnancy
edwards syndrome, turners, klinefelter
47XY + 18 = Edward syndrome (trisomy 18)
45 X = Turner syndrome
47 XXY = Klinefelter
is x chromosome aneuploidy better or worse tolerated? why?
X chromosome aneuploidy is better tolerated because of X inactivation
reproductive risks of reciprocal translocations
50% of conceptions will have either normal chromosomes or the balanced translocation
- Unbalanced products result in –
o Miscarriage – large segments
o Dysmorphic delayed child – small segments
molecular technique for genome wide testing
array comparative genomic hybridisation (aCGH)
molecular testing for specific chromosome
quantitive PCR
microoarray CGH
- Detects any missing or duplicated piece of chromosome
- Causative deletions possibly in up to 7% of children with learning disability
- Many deletions seen are neutral polymorphisms
- 1st line chromosome test!
how do deletions appear on aCGH?
half as much as DNA indicates a deletion
