GiM 1 Flashcards
What is Penetrance?
The frequency with which a specific genotype is expressed by those individuals that possess it, usually given as a percentage.
What is expressivity?
variation in expression - the extent to which a heritable trait is manifested by an individual
What is anticipation?
symptoms of a genetic disorder become apparent at an earlier age as it is passed from one generation to the next. In most cases there is an increase in the severity of symptoms too.
eg. Huntingtons disease
What is the risk to offspring of inheriting an autosomal dominant disorder?
1/2
What is the risk to offspring of inheriting an autosomal recessive disorder if both parents are carriers?
1/4
There are two carrier parents with an autosomal recessive disorder, what is the risk that their unaffected offspring are carriers?
2/3
Give some examples of disorders with X-linked inheritance
Duchenne Muscular dystrophy,
Fragile X syndrome
Red / green colour-blindness
Haemophilia
What will be the inheritance pattern of a father with haemophilia and a normal wife?
Xx = Carrier daughter (50%) XY = unaffected son (50%)
What is Lyonisation?
X-inactivation
When does X-inactivation occur?
In the blastocyst stage
What is the inactivated X chromosome in a cell called?
Barr body
Gives examples of X-linked dominant conditions
Rett syndrome - lethal in males, phenotype only in females
Fragile X syndrome – females:- asymptomatic to fully symptomatic,
due to X-inactivation pattern
Why do girls who are carriers of X-linked recessive disordered have varying levels of expression?
Approximately 50% of cells express the normal gene
Skewed X-inactivation – random preference
Tissue variability – random preference in crucial tissue group – eg muscle in Duchenne Muscular dystrophy
