Genetics

Question 1

What do the terms Penetrance, Incomplete dominance and Expressivity mean and give an example of each

Answer 1

Penetrance: proportion of individuals carrying a particular variant of a gene (allele or genotype) that also expresses an associated trait e.g. inherited breast cancer

Incomplete dominance: A heterozygotes phenotype is in between that of 2 homozygotes e.g. achondroplasia

Expressivity: have a particular genotype with varying severity of the phenotype e.g. polydactyly

Question 2

How are Autosomal dominant conditions identified in a pedigree?

Answer 2

vertical transmission, lack of skipped generations, male and female equally affected e.g. Huntington’s disease

Question 3

How are Autosomal recessive conditions identified in a pedigree?

Answer 3

phenotype affects siblings, male and female equally affected, skipping of generations, parents of affected child are carriers e.g. sickle cell anaemia, thalassaemia, albanism

Question 4

How are X-linked recessive conditions identified in a pedigree?

Answer 4

no father-son transmission, skip generations when passed through female carrier, males much more affected e.g. DMD, colourblindness