Genetic Terms

Question 1

Codominance

Answer 1

Both alleles contribute to the phenotype of the heterozygote (ex: Blood groups AB)

Question 2

Variable expressivity

Answer 2

People with the same genotypes have different phenotypes

Question 3

Incomplete penetrance (calculate risk of expressing phenotype)

Answer 3

Not all individuals with disease exhibit classic phenotypes of the disease.
% penetrance x probability of inheritance = risk of expressing phenotype

Question 4

Pleiotropy

Answer 4

One gene contributes to multiple phenotypes (PKU manifests as light skin, intellectual disability, and musty body odor)

Question 5

Anticipation

Answer 5

Increased severity or earlier onset (more severe outcome) in next generations

Question 6

Loss of heterozygosity

Answer 6

If a mutation is present in a tumor suppressor gene, the wild type allele must be deleted/mutated before cancer can develop. “Two-hit hypothesis”

Question 7

Epistasis

Answer 7

The allele of one gene affects the phenotype expression in another gene

Question 8

Aneuploidy (and due to what?)

Answer 8

An abnormal number of chromosomes due to chromosomal nondisjunction during mitosis/meiosis

Question 9

Dominant negative mutation

Answer 9

A heterozygote produces a nonfunctional mutant protein that also prevents the wild type protein from functioning. Exerts a dominant effect.

Question 10

Linkage disequilibrium

Answer 10

Tendency of alleles to occur in close proximity within the same chromosome more/less often than expected. Measured throughout populations

Question 11

Mosaicism

Answer 11

Genetically different cells in the same tissues/organs

Somatic: mutation from mitotic errors
Germline: mutation from egg/sperm cells

Question 12

Locus heterogeneity

Answer 12

Mutations at different loci resulting in the same disease

Question 13

Allelic heterogeneity

Answer 13

Same locus, different mutations, result in the same disease

Question 14

Heteroplasmy

Answer 14

Normal and mutated mtDNA resulting in variable expression in mitochondrial disease. To distinguish between all the other heteros remember heteroplasMy = mitochondria

Question 15

Uniparental disomy

Answer 15

Offspring receives 2 copies of a chromosome from one parent and NONE from the other parent.

Heterodisomy (one I) = heterozygous meiosis I error
Isodisomy (two I’s) = homozygous meiosis II error or postzygotic chromosomal duplication of one pair of chromosome and complete loss of the other original pair