Biochem 84

Question 1

Define codominance

Answer 1

Both alleles contribute to the phenotype of the heterozygote

Question 2

Examples of codominance?

Answer 2

1) Blood groups

2) Alpha-1 antitripsin deficiency

Question 3

Define variable expressivity

Answer 3

Phenotype varies among individuals with same genotype

Question 4

Example of variable expressivity

Answer 4

NF-1

Question 5

Define incomplete penetrance

Answer 5

Not all individuals with mutant genotype show mutant phenotype

Question 6

Example of incomplete penetrance

Answer 6

BRCA1 gene does not always result in breast or ovarian cancer

Question 7

Define pleiotropy

Answer 7

One gene contributes to multiple phenotypic effects

Question 8

Example of pleiotropy

Answer 8

Untreated PKU

Question 9

Define anticipation

Answer 9

Increased severity or earlier onset of disease in succeeding generations

Question 10

Example of anticipation

Answer 10

Trinucleotide repeat disorders (e.g. Huntingtons)

Question 11

Define loss of heterozygosity

Answer 11

If a patient inherits or develops a mutation or deletion of a tumor suppressor gene, the complementary allele must be deleted/mutated before cancer can occur.

note: this is not true of oncogenes

Question 12

Example of loss of heterozygosity

Answer 12

Retinoblastoma and the “two hit hypothesis”

Question 13

Define dominant negative mutation

Answer 13

Exerts a dominant effect.

A heterozygote produces a nonfunctional altered protein that prevents the normal gene product from functioning

Question 14

Example of negative dominant effect

Answer 14

Mutation of a transcription factor in its allosteric site

Question 15

Define linkage disequilibrium

Answer 15

Tendency for certain alleles at 2 linked loci to occur together more often than expected by chance.

Measure in populations not famiies

Question 16

Define mosaicism

Answer 16

Presence of genetically distinct cell lines in the same individual

Question 17

Mosaicism arises from what?

Answer 17

Mitotic errors after fertilization

Question 18

What is the difference between somatic mosaicism and gonadal mosaicism?

Answer 18

Somatic: mutation propagates through multiple tissues or organs
Gonadal: mutation only in egg or sperm cells

Question 19

Example of mosaicism

Answer 19

McCune-Albright syndrome

- lethal if the mutation is somatic, but survivable if mosaic

Question 20

Define locus heterogeneity

Answer 20

Mutations at different loci can produce a similar phenotype

Question 21

Example of locus heterogeneity

Answer 21

Albinism

Question 22

Example of allelic heterogeneity

Answer 22

B-thalassemia

Question 23

Define allelic heterogeneity

Answer 23

Different mutations in the same locus produce the same phenotype

Question 24

Define heteroplasmy

Answer 24

Presence of both normal and mutated mtDNA, resulting in variable expression in mitochondrial inherited disease