Genetics

Question 1

KRAS

Answer 1

KRAS is an oncogene present on chromosome 12p. It is involved in the pathogenesis of many different cancers: including colorectal and pancreatic cancers. In fact 90% of pancreatic cancers have the presence of a mutation in the gene.

Question 2

How do you calculate carrier frequency from the incidence?

Answer 2

Carrier frequency is calculated by the square root of (incidence/4)

Question 3

Locus heterogeneity

Answer 3

• ## mutations at different genetic loci (genes) that can cause the same or a similar phenotype

Question 4

Inheritence

Ehler Danlos

Question 5

Inheritance

G6pd

Question 6

Achondroplasia

inheritance

Question 7

Which chromosome is the CFTR gene on?

Answer 7

Chr 7

Question 8

myotonic dystrophy

Answer 8

DMPK gene

Question 9

Allelic heterogeneity

Answer 9

Allelic heterogeneity refers to a variety of alleles of a single gene (locus) that can all cause the same or a similar phenotype.

Answer 10

Variable expressivity refers to variation in the nature and severity of a phenotype. This is a frequent characteristic of autosomal dominant diseases that can affect multiple organ systems. In this example, the nature of the MEN-II phenotype can vary: affected patients may have medullary thyroid carcinoma or pheochromocytoma or hyperparathyroidism.
Variable expressivity should not be confused with penetrance, which refers to the clinical expression, or lack of it, of a mutant gene. Thus penetrance is an all-or-none phenomenon.

Locus heterogeneity is a single disorder, trait, or pattern of traits caused by mutations in genes at different chromosomal loci. For example, retinitis pigmentosa has autosomal dominant, autosomal recessive, X-linked and Y-linked origins. However, only one mutant locus is needed for the phenotype to manifest. Other examples are hypertrophic cardiomyopathy, osteogenesis imperfecta, Familial hypercholesterolemia

Answer 11

Homocystinuria is an autosomal recessive disorder. It is typically a disorder of the metabolism of the amino acid methionine due to a deficiency of cystathionine beta synthase.
Downward lens dislocation is most typical of this condition, where as superior lens dislocation is more typical of marfans syndrome

Question 12

CVS

Answer 12

invasive gentic testing
From 11 weeks
Sample of placenta
miscarriage risk of 1-2%

Question 13

Amniocentesis

Answer 13

From 16 weeks
Sample of amniotic fluid
miscarriage risk of 0.5-1%

Question 14

PGD

Answer 14

requires prior identification of specific familial gene/chromosome variation in the family

Question 15

Carrier testing

Answer 15

Genetic rest is asymptomatic individual to clarify their genetic status for a condition

specifically in AR or XR conditions

Question 16

Predictive testing

Answer 16

genetic test in a presymptomatic individual to clarify their future risk of developing a condition

Examples:
- HD
- - MD
- SCA
- PKD
- CM
- LQT
- Marfans

Adv:
- implementation of medical managment
- modify lifestyle choice, reproductive choice
- relieve anxiety