Biochemistry- Genetics

Question 1

Codominance

Answer 1

btoh alleles contribute to the phenotype of the heterozygote. Example blood groups

Question 2

Variable Expressivity

Answer 2

Phenotype varies among individuals with same genotype

Question 3

Incomplete penetrance

Answer 3

Not all individuals with a mutant genotype show the mutant phenotype

Question 4

Pleiotropy

Answer 4

One gene contributes to multiple phenotypic effects

Question 5

Anticipation

Answer 5

Increased severity or earlier onset of disease in succeeding generations like Huntington disease

Question 6

Loss of heterozygosity

Answer 6

If a patient inherits or develops a mutation in a tumor suppressor gene, the complementary allele must be deleted/mutated before cancer develops. E.g. retinoblastoma and the “two-hit hypothesis”

Question 7

Dominant negative mutation

Answer 7

Exerts a dominant effect. A heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning. Example: mutation of a transcription factor in its allosteric site. Nonfuncitoning mutant can still bind DNA, preventing wild-type transciption factor from binding.

Question 8

Linkage Disequilibrium

Answer 8

Tendency for certain alleles at 2 linked loci to occur together more often than expected by chance. Measured in a population, not in a family, and often varies in different populations

Question 9

Mosiacism

Answer 9

Presence of genetically distinct cell lines in the same individual. Arises from mitotic errors after fertilization. Example: McCune-Albright syndrome is lethal if the mutation is somatic, but survivable if mosaic

Question 10

Somatic mosiacism

Answer 10

Mutation propagates through multiple tissues or organs

Question 11

Gonadal mosiacism

Answer 11

Mutation only in egg or sperm

Question 12

Locus Heterogeneity

Answer 12

Mutations at different loci can produce a similar phenotype. Example: albinism

Question 13

Allelic heterogeneity

Answer 13

Different mutations in the same locus produce the same phenotype. Example: beta-thalassemia

Question 14

Heteroplasmy

Answer 14

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

Question 15

Uniparental Disomy

Answer 15

Offspring receives 2 copies of a chromosome from 1 parent and no copies from the other parent. Heterodisomy (heterozygous) indicates a meiosis I error. Isodisomy (homozygous) indicates a meiosis II error or postzygotic chromosomal duplication of one of a pair of chromosomes, and loss of the other of the original pair.

Question 16

Imprinting

Answer 16

At some loci, only one allele is active; the other is inactive (imprinted/inactivated by methylation). WIth one allele inactivated, deletion of the active allele leads to disease

Question 17

Give an example of imprinting.

Answer 17

Prader-willi and Angelman syndrome are due to mutations or deletions of genes on chromosome 15