Genetics Vocab
This term describes a unique chromosomal location.
Locus
This is the most abundant type of human genetic variation and involves variation at a single nucleotide.
SNV
A nucleotide substitution changes a codon but does not change the encoded amino acid.
silent variant
What is loss of function mutation?
Mutations that decrease protein activity or expression.
What does monogenic mean?
A disease caused primarily by one variant with a large effect.
An individual has two different alleles at the same locus. This term describes that condition.
Heterozygosity
what is a polymorphism?
A variant occurring at a minor allele frequency greater than 1% is classified by the slides using this term.
what is a missense variant?
A nucleotide substitution changes one amino acid to another.
A regulatory mutation increases expression of a gene. Functionally, this could represent this type of mutation.
Gain-of-function mutation
What is the opposite of monogenic?
polygenic.
This is a combination of alleles located on the same chromosome.
Haplotype
In a population, allele A occurs 30 times and allele G occurs 70 times. Give the minor allele frequency.
0.3 or 30%
Nonsense variant
A nucleotide substitution creates a premature termination codon.
Name the mechanism:
A patient has one normal allele and one null allele. The normal allele produces protein, but 50% of the usual amount is insufficient for a normal phenotype.
haploinsufficiency
In general, disease alleles with very large effects tend to be rare, while alleles with smaller effects can have this population characteristic. Why?
negative selection.
A mutation occurs in a body cell after conception, producing populations of cells with different genotypes. This phenomenon is called this.
Mosaicism
A DNA sequence of approximately 1 kb–1 Mb whose number of copies differs between alleles is called this. (Bonus 100, what is the other type of structural variation?)
CNV
An insertion of two nucleotides into a coding region would most likely create this type of variant.
frameshift variant
A mutant protein physically interferes with protein made by the normal allele, causing disease even in a heterozygote. what is this called?
dominant-negative effect.
Explain liability threshold model.
Under this model, genetic and environmental influences combine to create a continuous susceptibility, and disease occurs once an individual crosses a threshold.
One allele produces a phenotype even when paired with a different allele, whereas the other produces its effect only when homozygous. Name the two allele types.
Dominant and recessive
Among carriers of allele A, 12 individuals have disease and 4 do not. Among noncarriers, 6 have disease and 8 do not. Calculate the allelic odds ratio.
(12/4) ÷ (6/8) = 3 ÷ 0.75 = 4.
What is NMD?
nonsense-mediated mRNA decay, a premature termination codon can trigger degradation of the abnormal mRNA, reducing protein expression.
Loss of function variants are usually recessive, but what are the two special cases?
Haploinsufficiency and dominant-negative effect.
What is GWAS?
Genome wide association study: a study design where researchers genotype roughly 1-2 million SNVs across large groups of cases and controls and look for allele-frequency differences associated with disease.