Genetic terminology

Question 1

Codominance

Answer 1

Both alleles contribute to the phenotype of the heterozygote

( 2 alleles but neither is dominant)

Blood groups A, B, AB, and alpha-antitrypsin deficiency

Question 2

Variable expression

Answer 2

Phenotype varies among ppl with the same genotype

Neurofibromatosis type 1 may different in severity despite same genotype

Question 3

Incomplete penetrance

Answer 3

Not all individuals with the mutant genotype show the mutant phenotype

BRCA1 gene mutations do not always result in breast or ovarian cancer.

Question 4

Pleiotropy

Answer 4

One gene contribute to multiple phenotypic effects

Untreated phenylketonuria (PKU) – manifest with light skin, intellectual disability, an dusty body odor

Question 5

Anticipation

Answer 5

increased severity or earlier onset of disease in succeeding generations

ex. Huntington’s disease, Alzheimer’s.

Question 6

Loss of heterozygosity

Answer 6

Inherited/aquired mutation of a tumor suppressor gene will not cause cancer until the complementary allele is deleted or mutated as well.

Retinoblastoma ( two-hit hypothesis)

Question 7

Dominant negative mutation

Answer 7

Heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning

• mutation of a transcription factor in its allosteric site.
• nonfunctional mutant can still bind to DNA and therefore, prevents wild-type transcription factor from binding.
• decrease in transcription

Question 8

linkage disequilibrium

Answer 8

a pair of alleles from two loci are inherited together in the same gamete more or less often than would be expected by chance.

Question 9

Mosaicism

Answer 9

Presence of genetically distinct cel lines in the same individual

Somatic mosaicism – mutations arise due to mitotic errors after fertilization and propagates through multiple tissues and organs

Gonadal mosacisim – mutation only in egg or sperm

ex. McCune Albright syndrome – mutation in G protein signaling.

Question 10

Locus herterogeneity

Answer 10

Mutations at different loci can produce similar phenotype

• Albinism
• Marphan syndrome, MEN2B, homocysteinuria = Marfan habitus

Question 11

Allelic heterogeneity

Answer 11

Different mutations in the same locus produce the same phenotype

Beta- thalassemia

Question 12

Heteroplasmy

Answer 12

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

Question 13

Uniparental disomy

Answer 13

Offspring receives 2 copies of a chromosome from 1 parent and no copies from the other parent

child is still euploid ( correct number of chromosomes)