Modes of inheritance

Question 1

Define autosomal dominant inheritance…

Answer 1

One pathogenic variant allele on an autosomal chromosome sufficient for individual to become affected by a disease. e.g. Lynch, Huntington’s

Question 2

Define autosomal recessive inheritance…

Answer 2

Both copies of alleles must have a pathogenic variant for phenotypic presentation e.g. CF, Sickle cell

Question 3

Define X-Linked dominant inheritance…

Answer 3

Pathogenic variant on X chromosome.

Typically more penetrant and expressive in males

Males will pass on to 100% of daughters, 0% males

E.g. Fragile X

Question 4

Define X-Linked recessive inheritance…

Answer 4

Pathogenic variant allele on X chromosome; two copies required in females (XX), on the only copy in males (XY). Males much more likely to be affected.

e.g. DMD/BMD

Question 5

Define co-dominant inheritance…

Answer 5

In codominant inheritance, two different versions (alleles) of a gene are expressed, and each version makes a slightly different protein. Both alleles influence the genetic trait or determine the characteristics of the genetic condition.

E.g. ABO blood types

Question 6

Define mitochondrial inheritance…

Answer 6

Pathogenic variant in mitochondrial DNA (mtDNA)

Maternal only e.g. Leber hereditary optic neuropathy

Question 7

Define what a chromosomal abonormalities are…

Answer 7

Due to mitotic or meiotic non-disjunction to form aneuploidy, structural rearrangements to form breakages).

e.g. Trisomy 21