Autosomal dominant and recessive inheritance

Question 1

Autosomal dominant inheritance characteristics

Answer 1

Autosomal means it is of somatic cells
- Heterozygote parent and unaffected parent
- equal number of male and females affected
- No skipping generation
- Father to son transmission may be observed
- dominant disease allele will produce disease in heterozygote

Question 2

Recurrence risk for AD disorder

Answer 2

is 50%

Question 3

Autosomal recessive inheritance (quasidominant inheritance) characteristics

Answer 3

• mostly heterozygote parents
• equal number of male and females affected
• Skip generation
• not usually present in earlier generations but clustering of disease phenotype among the siblings
• Consanguinity is sometimes seen (mating between close relatives - common ancestors)
• recessive disease allele will not produce disease in heterozygote

Question 4

Recurrence risk for AR disorder

Answer 4

is 25% but Quasi dominant inheritance, with a recurrence risk of 50%, is seen when an affected homozygote mates with a heterozygote

Question 5

quasidominant inheritance

Answer 5

In AR disease, When a heterozygote parent carrier mate with affected homozygote parent leads to recurrence risk of 50% is then called quasidominant

Question 6

De novo mutation

Answer 6

occurrence of genetic disease in a person with no family history of that disease and their siblings are also risk free but risk will increase for the offspring of an affected individual.

Question 7

Germline mosaicism

Answer 7

Mosaicism is presence of more than one genetically distinctive cell line in the body and it occurs when one of the parents has their part or all of the germline cells affected by mutation but not the somatic cells which then produces mosaic of mutated and non-mutated cells in the offspring and increase the recurrent risk of successive generations of that offspring. eg: osteogenic Imperfecta

Question 8

Reduced penetrance

Answer 8

is when a person carrying disease causing genotype is not showing disease phenotype. Eg: retinoblastoma

Question 9

Age dependent penetrance

Answer 9

Delay in age related onset of genetic disease - disease phenotype is not present straight after birth but it becomes apparent at adulthood. Eg: Huntington’s disease

Question 10

Locus heterogeneity

Answer 10

Disease caused by mutation at different loci in different families is said to exhibit locus heterogeneity

Question 10

Pleiotropy

Answer 10

Gene that affects multiple organ systems is known as pleiotropic