Genetics Flashcards
(28 cards)
briefly describe the phases of mitosis
- prophase - chromosomes condense, spindle forms and nucleolus disappears
- metaphase - spindle captures all the chromosomes and lines them up at the middle of the cell
- Anaphase - sister chromatids separate from each other and are pulled toward opposite ends of the cell
- telophase - mitotic spindle broken down, two nuclei form, chromosomes decondense
at what phase of the cell cycle does DNA replicate
S phase of interphase
timing of FTCS, MSST and NIPS
FTCS - 11+0 to 13+6
MSST - 15-20
NIPT >10
FTCS incorporates what
maternal age US measurement of NT serum levels of: - PAPP-A - free bhCG
what is the sensitivity and specificity of FTCS, MSST and NIPT for T21
FTCS - sensitivity 85% - specificity 95% MSST - sensitivity 70-75% - specificity 93% NIPT - 99% for both
MSST incorporates what
maternal age serum levels of: - free bhCG - alpha fetal protein - unconjugated oestriol - inhibin A
timing of CVS and amnio
CVS 11-14
Amnio 15-20
quoted risk of miscarriage after CVS and amnio
CVS 1%
Amnio 0.5%
what is the risk of doing a CVS prior to 11 weeks
increased risk of transverse limb reduction defects
when and what cells are removed for PIGD
performed at blastocyst stage
- 5-8 trophoectoderm cells extracted
risk of T21 across maternal ages
age 25 - 1:1200
age 35 - 1:300
age 40 - 1:100
overall incidence of T21
1:400 recognized pregnancies
what levels of maternal serum markers in FTCS and MSST would make you think that T21 is higher risk
FTCS
- high PAPP-A
- low bhCG
MSST
- high bhCG
- low alpha fetal protein
- low unconjugated oestriol
what levels of maternal serum markers in FTCS would make you think that T18 is higher risk
very low bhCG
very low PAPP-A
incidence of Turner syndrome
1:2500 girl infants
incidence of CF
1:2500 newborns
carrier frequency of CF
1:25 in people of Northern European origin
what nationalities are more and less common to have CF
more common - Northern European, Ashkenazi Jews, Native Americans
less common - Asian, African, Southern European
describe the inheritance of CF and what gene is affected
- autosomal recessive condition
- defect in CFTR gene on chromosome 7 that codes for transmembrane chloride channel
- most common mutation is F508 deletion
- variable penetrance and phenotype
how does the CF mutation cause the phenotype see
mutation causes abnormalities in the transport of chloride across the epithelial and mucosal surfaces
- causes relative dehydration of airway secretions –> impaired mucociliary transport and airway obstruction
- causes abnormal pancreatic enzymes
what proportion of infants with CF does newborn screening pick up
90%
- differing sensitivities in different ethnic gruops
what is measured in CF newborn screening
level of serum trypsinogen
which populations have higher incidence of Tay Sachs
Ashkenazi Jews
French Canadian
Pennsylvania Dutch
describe the genetics of Tay-Sachs
Autosomal recessive inheritance
Mutation in HEXA gene
