Obstetric genetics Flashcards
What are the different types of inheritance
- autosomal dominant
- Autosomal recessive
- x-linked recessive
Whats autosomal dominant inheritance
Heterozygous with one copy of abnormal gene are affected
Whats autosomal recessive inheritance
`homozygous with two copies of the abnormal gene are affected
Whats x-linked recessive inheritance
Males which one copy of the abnormal gene on X-chromosome are affected
Who is not affected by x-linked inheritance
Carrier women
Who can’t x-linked inherited genes be passed on from-to
Male to male
Who are affected by x-linked recessive diseases
All men who inherit the mutation
Examples of x-linked diseases
- Haemophilia
- Duchene muscular dystrophy
common examples of recessive inherited diseases
- CF
- Haemochromatis
- Beta thaloesemia
What’s the chance of being a carrier when you are not affected, but your sibling is
2/3
Formula for risk
Risk in A x Risk in B x Probability that child will inherit 2 copies of the mutation
What formula do you use when you don’t know the carrier rate
Hardy Weinburg (as long as the gene frequency is in equilibrium)
When is chronic villus sampling done
11-13 weeks
How is chronic villus sampling done
needle stuck through stomach and chromosomes are tested
risks of chronic villus sampling
1% risk of miscarriage
When is amniocentesis done
15-16 weeks
Where are amniocytes derived from
Fetal tissue and amnion
How long does chromosome analysis in amniocentesis take
2-3 weeks
Negatives of amniocentesis
Low yield of fetal DNA, 1% miscarriage
What happens in PGD
1) stimulation ovulation
2) oocyte retrieval
3) fertilization and culture
4) blastocyst biopsy on day 5
When does transfer of embryos occur in PGD
embryos are frozen when testing takes place and the transfer of embryo occurs 2 months later
What is the live birth rate of PGD
35%
What gives a persons liability to be affected?
Sum of environmental and genetic predisposition
What is recurrence risk
Empiric figures from population studies
