Genetics

Question 1

Incomplete penetrance example

Answer 1

BRCA gene mutations do not always result in breast or ovarian cancer

Question 2

Loss of heterozygosity

Answer 2

Tumor suppressor genes require one mutation and deletion/mutation of second gene before cancer develops
NOT TRUE OF ONCOGENES 
Rb and two hit hypothesis 
Lynch syndrome 
Li-Fraumeni syndrome

Question 3

Linkage disequilibrium

Answer 3

Tendency for alleles at 2 linked loci to occur together more or less often than expected by chance. Measured in a population and varies with different populations.

Question 4

Mosaicism

Answer 4

Genetically distinct cell lines in the same individual
McCune-Albright syndrome: mutation in G protein signaling
–unilateral cafe-au-lair spots, precocious puberty, multiple endocrine abnormalities,

Question 5

McCune-Albright Syndrome

Answer 5

Mosaicism -only survivable in patients with Mosaicism
Mutation affecting G protein signaling
Unilateral cafe au lait spots
Polyostotic fibrous dysplasia, precocious puberty, multiple endocrine abnormalities
LETHAL if mutation is prior to fertilization

Question 6

Locus heterogeneity

Answer 6

Mutations at different loci can produce a similar phenotype

Ex: albinism

Question 7

Allelic heterogeneity

Answer 7

Different mutations in the same locus produce the same phenotype
Ex: beta thalassemia

Question 8

Heteroplasmy

Answer 8

Presence of both normal and mutated mtDNA

Variable expression in mitochondrially inherited disease

Question 9

Uniparental disomy

Answer 9

Consider in an individual manifesting with a recessive disorder when only one parent is a carrier

Question 10

Hardy Weinberg population

Answer 10

1. No mutation occurring at the locus
2. Natural selection not occurring
3. Completely random mating
4. No net migration

Question 11

Imprinting

Answer 11

Only one allele is active and the other one is inactive

Ex: angelman and prader-willi

Question 12

Prader-Willi syndrome

Answer 12

Paternal is mutated
Maternal imprinting–mother’s gene is usually silent (child may also receive two “silent” genes from the mother)
Child has hyperphagia, obesity, intellectual disability, hypogonadism and hypotonia
Will used to eat his feelings and was not aroused.

Question 13

Angelman syndrome

Answer 13

Maternal deleted/mutated
Paternal imprinting
“Happy puppet” – It’s all in their head (seeing Angels)
Seizures, ataxia, severe MR

Question 14

Pleiotropy

Answer 14

One gene contributes to multiple phenotypic effects

PKU-musty odor, light skin and intellectual disability

Question 15

Hypophosphatemic Rickets

Answer 15

X linked dominant
Vit D resistant Rickets
Increased phosphate wasting at proximal tubule

Question 16

Mitochondrial Inheritance

Answer 16

Mitochondrial myopathies
Lactic acidosis, CNS disease, myopathy
Ex: MELAS–failure in oxidative phosphorylation
“ragged red fibers” on muscle biopsy