Biochem - Genetics (Genetic terms, Hardy-Weinberg, & Imprinting) Flashcards

Pg. 84-85 in First Aid 2014 Sections include: -Genetic terms -Hardy-Weinberg population genetics -Imprinting

1
Q

What is the definition of codominance? Give 2 examples.

A

Both alleles contribute to the phenotype of the heterozygote; (1) Blood groups A, B, AB (2) alpha1-antitrypsin

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2
Q

What is the definition of variable expressivity? Give an example.

A

Phenotype varies among individuals with same genotype; 2 patients with neurofibromatosis type I (NF1) may have varying disease severity

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3
Q

What is the definition of incomplete penetrance? Give an example.

A

Not all individuals with a mutant genotype show the mutant phenotype; BRCA1 gene mutations do not always result in breast or ovarian cancer

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4
Q

What is the definition of pleiotropy? Give an example.

A

One gene contributes to multiple phenotypic effects; Untreated phenylketonuria (PKU) manifests with light skin, intellectual disability, and musty body odor

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5
Q

What is the definition of anticipation? Give an example.

A

Increased severity or earlier onset of disease in succeeding generations; Trinucleotide repeat diseases (e.g., Huntington disease)

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6
Q

Define loss of heterozygosity. To which genes does it apply versus does not apply? Give an example.

A

If a patient inherits or develops a mutation in a tumor suppressor gene, the complementary allele must be deleted/mutated before cancer develops. This not true of oncogenes; Retinoblastoma and the “two-hit hypothesis”

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7
Q

What is the definition of dominant negative mutation? Give an example.

A

Exerts a dominant effect. A heterozygotes produce a nonfunctional altered protein that also prevents the normal gene product from functioning; Mutation of a transcription factor in its allosteric site. Nonfunctioning mutant can still bind DNA, preventing wild-type transcription factor from binding

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8
Q

What is the definition of linkage disequilibrium? In what context is it measured, and by what does it often vary?

A

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

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9
Q

What is the definition of mosaicism? From what does it arise?

A

Presence of genetically distinct cell lines in the same individual; Arises form mitotic errors after fertilization;

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10
Q

What are the types of mosaicism? How does the mutation occur in each?

A

Somatic mosaicism - mutation propagates through multiple tissues or organs; Gonadal mosaicism - mutation only in egg or sperm cells

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11
Q

What clinical condition exemplifies mosaicism? How does it differ in somatic versus gonadal types?

A

McCune-Albright syndrome is lethal if the mutation is somatic, but survivable if gonadal

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12
Q

What is the definition of locus heterogeneity? Give an example.

A

Mutations at different loci can produce a similar phenotype; Albinism

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13
Q

What is the definition of allelic heterogeneity? Give an example.

A

Different mutations in the same locus produce the same phenotype; Beta-thalassemia

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14
Q

What is the definition of heteroplasmy?

A

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

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15
Q

What is the definition of uniparental disomy?

A

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

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16
Q

What are the types of uniparental disomy, and what kind of error is indicated by each?

A

(1) Heterodisomy (heterozygous) indicates a meiosis I error (2) 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

17
Q

What ploidy results from uniparental disomy?

A

Uniparental is eUploid (correct number of chromosomes), not aneuploid

18
Q

What kind of phenotype typically results from UPD?

A

Most occurrences of UPD –> normal phenotype

19
Q

In what clinical context should UPD be considered?

A

Consider UPD in an individual manifesting a recessive disorder when only one parent is a carrier

20
Q

What are the 4 assumptions made in the Hardy-Weinberg law?

A

Hardy-Weinberg law assumptions include: (1) No mutation occurring at the locus (2) Natural selection is not occurring (3) Completely random mating (4) No net migration

21
Q

Give and define the equations that apply if a population is in Hardy-Weinberg equilibrium.

A

If a population is in Hardy-Weinberg equilibrium and if p and q are frequencies of separate alleles, then: p^2 + 2pq + q^2 = 1 and p + q = 1, which implies that: p^2 = frequency of homozygosity for allele p, q^2 = frequency of homozygosity for allele q, 2pq = frequency of heterozygosity (carrier frequency, if an autosomal recessive disease)

22
Q

According Hardy-Weinberg equilibrium, what is the frequency of an X-linked recessive disease in males versus females?

A

The frequency of an X-linked recessive disease in males = q and in females = q^2

23
Q

Draw a Punnett Square using Hardy-Weinberg equations.

A

See p. 85 in First Aid 2014 for visual

24
Q

What is imprinting? How does this lead to disease?

A

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 –> disease.

25
Q

What mutation causes both Prader-Willi and Angelmann syndromes? What genetic term can also cause such imprinting?

A

Both Prader-Willi and Angelmann syndromes are due to mutation or deletion of genes on chromosome 15; Can also occur as a result of uniparental disomy

26
Q

What defines Prader-Willi syndrome?

A

Maternal imprinting: gene from mom is normally silent and Paternal gene is deleted/mutated; Think: “ P for Prader & Paternal”

27
Q

What are 5 characteristics in the presentation of Prader-Willi syndrome?

A

Results in (1) hyperphagia (2) obesity (3) intellectual disability (4) hypogonadism (5) hypotonia

28
Q

What defines Angelman syndrome?

A

Paternal imprinting: gene from dad is normally silent and Maternal gene is deleted/mutated; Think: “M for angelMan & Maternal”

29
Q

What are 4 characteristics in the presentation of Angelman syndrome?

A

Results in (1) inappropriate laughter (“happy puppet”) (2) seizures (3) ataxia (4) severe intellectual disability.

30
Q

What percentage of Prader-Willi syndrome cases are due to maternal uniparental disomy? What does this mean?

A

25% of cases due to maternal uniparental disomy (two maternally imprinted genes are received; no paternal gene received)

31
Q

What percentage of Angelman syndrome cases are due to paternal uniparental disomy? What does this mean?

A

5% of cases due to parental uniparental disomy (two paternally imprinted genes are received; no maternal gene received)