Genetics Flashcards
(41 cards)
What is a Robertsonian Translocation?
Where chromosomes break at their centromeres and the long arms fuse to form a single large chromosome.
Define deformation.
Distortion of a structure by mechanical force.
Define dysplasia.
Abnormal organisation of tissue. Pre-cancerous cells which show the genetic and cytological features of malignancy but not invading the underlying tissue.
What is genetic imprinting?
Where genes are expressed differently according to whether they’re inherited on the maternal or paternal chromosome.
What weeks of gestation are each trimester?
1st = 1-12 2nd = 13-26 3rd = 27-40
What are the purposes of the 12 week scan?
Date the pregnancy accurately Diagnose multiple pregnancy Diagnose major foetal abnormalities Diagnose early miscarriage Assess DS risk and other chromosomal abnormalities
What is nuchal translucency?
Thickness of the fluid at the back of the foetal neck.
How is nuchal translucency used in diagnosis.
Should be <3mm
>3mm indicates DS, Patau, Turner’s, Edward’s.
What are the routine ultrasound scans in a pregnancy?
Nuchal scan - 10-14 weeks
Mid-trimester anomaly scan - 20-22 weeks
When can cell-free foetal DNA (cffDNA) be detected in the maternal plasma?
First detectable after 4-5 weeks gestation. Accurate detection after 9 weeks gestation.
How can cffDNA be used to diagnose aneuploidy conditions?
Amount of cffDNA for particular chromosomes will be more/less than expected. E.g. for trisomy 21, more chromosome 21 detected than expected.
How can cffDNA be used to assess risk of x-linked conditions.
SRY gene detected enabling determination of sex. If female, no risk.
Discuss limitations of cffDNA as a technique.
In multiple pregnancies, not possible to tell which foetus DNA is from.
In women with high BMI, cffDNA reduced.
What is chorionic villus sampling (CVS)?
An invasive transabdominal/transvaginal technique where a sample of the chorionic villi is taken. Chorionic villi = part of the developing placenta: have the same DNA as the foetus. Test can be conducted from 11-14 weeks. 1-2% miscarriage risk.
What is an amniocentesis test?
A sample of the amniotic fluid (which contains foetal cells) is taken. Test can be conducted from 16 weeks. 1% miscarriage risk.
What does PGD stand for?
Pre-implantation Genetic Diagnosis.
What is a single nucleotide polymorphism (SNP)?
A mutation present in at least 1% of the population.
What is cystic fibrosis and how is it caused?
It is a monogenic autosomal recessive disease caused by mutations in the CFTR gene. This mutation affects the chloride ion channels, leading to excessive mucous production in airways and pancreas, affecting breathing and secretion of pancreatic enzymes.
Define penetrance.
The proportion of individuals of a population with a specific allele that also have the expected phenotype (they express the associated trait).
Define variable expressivity.
Phenotype expressed to a different degree in individuals with the same genotype.
Define consanguinity.
Inbreeding between 2nd cousins or closer.
What are obligate carriers.
Clinically unaffected people who carry a gene mutation based on their family history (autosomal recessive or x-linked).
What is the difference between the proband and the consultand?
The proband is the first affected family member who seeks medical attention for a genetic disorder
The consultand is the person about whose future offspring the genetic counsellor is about to make predictions.
What is the difference between anaphase in mitosis and anaphase I in meiosis?
In mitosis, the SISTER CHROMATIDS are pulled apart.
In meiosis, the HOMOLOGOUS PAIRS are pulled apart.
