Topic 7: Genetics, Allelic Relationships, and Gene Interactions

Vocabulary flashcards covering Topic 7 genetics concepts, including allele interactions, dominance, biochemical pathways, mutations, and epistatic gene interactions.

Recombination

offspring derive a combination of alleles different from their parents, occurring via independent assortment or crossing over.

Mutation hotspot

A site in a gene that mutates more frequently than other sites.

Intragenic

Occurring within the same gene.

Intergenic

Occurring between different genes.

Auxotroph

A mutant microorganism that can grow on minimal medium only if it has been supplemented with one or more nutrients not required by the wild type strain.

Prototroph

A microorganism (usually wild type) that can grow on minimal medium without supplemental nutrients.

Arginine Biosynthetic Pathway (One Gene, One Enzyme)

The biochemical pathway where a precursor is converted to arginine.

Isolate mutations that disrupt arg synthesis

Complex / multifactorial traits

Traits controlled by multiple genes and also influenced by environmental factors.

Discrete trait

A trait that is either present or not present.

Continuous trait

A trait that individuals possess in varying degrees.

Incomplete dominance

two alleles of a gene where the heterozygote displays a phenotype intermediate between that of the two homozygotes (for example, $AA$ = blue, $aa$ = red, $Aa$ = purple).

Codominance

two alleles of a gene where the heterozygote exhibits the phenotype of both homozygotes.

Dominance series

The dominance relations of all possible pairs of alleles listed in linear order.

Mutation

A heritable alteration in DNA sequence.

Allele frequency

The proportion of all copies of a gene in a population that are of a given allele type.

Wild type allele

An allele or DNA variant whose frequency is more than $1\%$ in a population, or the allele that dictates the most frequently observed phenotype in a population (designated with a superscript $+$).

Mutant allele

An allele or DNA variant whose frequency is less than $1\%$ in a population, or an allele that causes a phenotype seen only rarely in a population.

Polymorphic

locus having 2+ distinct alleles in a population.

Common variant

A high-frequency allele of a polymorphic gene.

Pleiotropy

single gene determines a number of distinct and seemingly unrelated characteristics.

Recessive lethality

prevents the survival of homozygotes, while heterozygotes carrying the allele survive.

Epistasis

A gene interaction in which one gene masks the phenotypic effects of another gene.

Modifier genes

Genes that produce a subtle, secondary effect on phenotype. No formed distinction exists between primary and modifier genes

How is expression of a genotype modified

Modifier genes, environment, and chance

Penetrance

Fraction of individuals with particular genotype that show the associated phenotype

Incomplete penetrance

Not every genotype is expressed

Expressivity

Degree or intensity with which a particular genotype is expressed as a phenotype

Temperature sensitive allele

Use tyrosinase to convert precursor to melanin

Recessive epistasis

homozygosity for a recessive allele of one gene hides the effect of a second gene (examples include Labrador retrievers, the Bombay phenotype, and white clover).

Reciprocal recessive epistasis

A type of gene interaction that results in a $9:7$ phenotypic ratio.

Linimarase

Converts precursor to HCN

Dominant epistasis

dominant allele of one gene masks the effect of another gene, yielding phenotypic ratios such as $12:3:1$ or $13:3$.

redundancy

A situation where a dominant allele of either gene is sufficient for normal phenotype/function ($A\_$ or $B\_$), producing a $15:1$ ratio.

Complementation test

A genetic test used to determine whether two independent mutations are located within the same gene or in different genes.

Complementation (Complementation test outcome)

wild-type phenotype = mutations occurred in different genes.

Non-complementation (Complementation test outcome)

mutant phenotype = mutations occurred in the same gene.

Heterogeneous traits

Phenotypic characteristics or traits caused by a mutation in any one of a number of different genes.