Genetics in clinical practice 1

Question 1

What is the difference between phenotypic heterogeneity and genetic heterogeneity

Answer 1

Phenotypic -different mutations in the same gene that can sometimes give rise to strikingly different phenotypes
Genetic - mutations at two or more genetic loci that produce the same or similar phenotypes

Question 2

Autosomal dominant condition

Answer 2

transmitted from generation to generation (vertical inheritance)
male and female equally affected, affected parent of either sex can pass onto both sons and daughters (variable condition, variable expression)

Question 3

What is penetrance

Answer 3

proportion of carriers who manifest phenotypic signs of conditions. Not all individuals who inherit a dominant disease mutation necessarily show signs of it e.g. cherubism, age specific penetrance

Question 4

What does tertralogy of fallot involve

Answer 4

narrow pulmonary valve, thick RV, large over riding aorta, ventricular septal defect

Question 5

For some autosomal dominant diseases, the parents may not present with symptoms but their children might. Why

Answer 5

Even if exclude non paternity, a parent could carry a small proportion of gametes (germline cells that harbour the same mutation

Question 6

Autosomal recessive

Answer 6

Male and female can equally be affected

Generally only members of single sibship/cousinss affected

Question 7

Compound heterozygosity give examples and define

Answer 7

Different allelic mutation in same genes/locus

e.g. sickle cell anaemia

Question 8

X linked recessive

Answer 8

only males related via the female line are affected, woman usually asymptomatic. Sons of affected male are not affected

Question 9

What happens during X inactivation

Answer 9

Only one X ussed per cell->dosage compensation_
Only X in each ccell sqitched off before blastocyst implants in female embryos. Female embryos are mosaic only expressing either paternal or maternall X but nost

Question 10

X linked dominant

Answer 10

Males and femaales affected (femaless

Question 11

X linked dominant example

Answer 11

Incontinentia pigmenti, Goltz focal dermal hypoplasia