Genetics

Question 1

Genomic imprinting

Answer 1

Methylation- down regulation.

Question 2

Uniparental disomy

Clinical correlates

Answer 2

Two chromosomes from the same parent that have parent specific imprinting = no gene product.

- Beckwith-Weidemann
Uniparental disomy of chromosome 11.
- Prader Willi Syndrome
Paternal Deletion in chromosome 15 
-Angelman Syndrome 
Maternal deletion on chromosome 15

Question 3

Autosomal dominant inheritance

Answer 3

Only 1 allele needed for expression.

Both males and females.

Recurrent risk is 50%

Expected in every generation.

Affected offspring have one affected parent.

Ex: postaxial polydactyly

Question 4

Autosomal recessive inheritance.

Answer 4

2 copies of gene needed to influence phenotype.

Heterozygotes are carriers.

Affected individuals have normal parents.

Both males and females affected.

More likely with consanguinity.

Ex: Tyrosinase Negative Albanian

Question 5

X-linked recessive inheritance

Answer 5

Males, one X.
- Disease allele on X in males termed hemizygous. Females can be homozygous.

No male carriers, female carriers can transmit disease allele.

All daughters of affected males are heterozygous.

Ex: Duchenne Muscular Dystrophy

Question 6

X-linked dominant

Answer 6

Very rare, no carriers.

Males with disease allele transmit the trait only to females with 100%!transmission.

Females with disease allele transmit the trait to both males and females, 50% transmission

Ex: Hypophosphatemia
- low phosphorus in blood due to defective reabsorption of phosphate in kidney. Short stature, deficient absorption of Ca in intestines causes soft bones (Rickets). Abnormal VitD metabolism. Treat with oral phosphate and Vit D.

Question 7

Locus heterogeneity

Answer 7

Single disorder, trait, or pattern of traits caused by mutations in genes at different chromosomal loci.

Ex: Osteogenesis Imperfecta
- brittle bone disease. Mutations in collagen genes (two loci: chromosome 7 and 17), either mutation exhibits the same phenotype