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Flashcards in Genetic Terms Deck (14):
1

Both alleles contribute to the phenotype of the heterzygote

Codominance
Examples- blood groups, alpha antitrypsin def, HLA groups

2

Patients with the same genotype have varying phenotypes

Variable expressivity
Ex: 2 patients with NF1 have differing severities of disease

3

Not all individuals with a mutant genotype show the mutant phenotype

Incomplete penetrate- % penetrance x probability of inheriting genotype= risk of expressing penetrance
Ex: BRCA1 genes don’t always result in breast or ovarian cancer

4

One gene contributes to multiple phenotypic effects

Pleiotropy
Ex: untreated PKU manifests with light skin, intellectual disability, and must body odor

5

Increased severity or earlier onset of disease in succeeding generations

Anticipation
Ex: Huntington’s disease with trinucleotide repeats

6

If a patient inherits or develops a mutation in a tumor suppressor gene, the complementary allele must be deleted/mutated before cancer develops. (Not true of oncogenes)

Loss of heterozygosity
Ex: Rb and two hit hypothesis, HNPCC, Li-Fraumeni syndrome

7

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

Dominant negative mutation
Ex: mutation of a TF in its allosteric site. Non functioning mutant can still bind DNA, preventing wild type transcription factor from binding.

8

Tendency of certain alleles at 2 closely spaced loci to occur together more or less often than expected by chance. Measured in population, not in a family, and often varies in different populations

Linkage disequilibrium

9

Presence of genetically distinct cell lines in the same individual

Mosaicism
Somatic- mutations arises from mitotic errors after fertilization and propagates through multiple tissues or organs
Gonadal- mutation only in the egg or sperm cells. If parents and relatives do not have the disease, suspect germline mosaicism
Ex: McCune Albright syndrome- due to mutation affecting G protein signaling. Presents with cafe-au-last spots with ragged edges, polyostotic fibrous dysplasia, and one endocrinopathy. Lethal if mutation occurs before fertilization, but survivable in mosaicism.

10

Mutations at different loci can produce a similar phenotype

Locus heterogeneity
Ex: Albinism

11

Different mutations in same locus produces the same phenotype

Allergic heterogeneity
Ex: Beta thalassemia

12

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

Heteroplasmy
MtDNA passed from mother to all children

13

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

Uniparental disomy- euploid(correct # of chromosomes) so most can have normal phenotype
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.

Ex: UPD in an individual manifesting a recessive disorder when only one parent is a carrier- angel an or prader willi syndromes.

14

One gene copy is silenced by methylation, and only the other copy is expressed to get the parent of origin effects

Imprinting
PW syndrome- maternally imprinted (maternal genes are silenced) so disease occurs when PATERNAL allele is mutated/deleted. Chromosome 15 mutation on paternal allele or maternal uniparental disomy.
Angelman- paternal imprinted (paternal UBE3A gene is silenced) and disease occurs if MATERNAL allele is deleted or mutated. Chromosome 15 mutations on maternal allele or paternal uniparental disomy.