Extensions of Mendelian Genetics Flashcards

Vocabulary flashcards based on lecture notes about extensions of Mendelian genetics.

Alleles

Alternative forms of a gene.

Mutation

The ultimate source of alleles; New phenotypes result from changes in functional activity of gene product.

Wild-type (wt) allele

Occurs most frequently in nature and is usually, but not always, dominant.

Loss-of-function mutations

New phenotype results from change in activity; Mutation causes loss of wild-type function.

Gain-of-function mutations

Mutation enhances function of wild type; Quantity of gene product increases.

Neutral mutation

Gene product has no change in phenotype.

Incomplete or Partial Dominance

Intermediate phenotype; Neither allele is dominant; Ratio is 1:2:1 in F2. Phenotypic and genotypic ratios are the same; Each genotype has its own phenotype.

Incomplete dominance in humans (Tay-Sachs disease)

Normal heterozygotes: have one copy of mutant gene, resulting in 1/2 wt enzyme activity compared to homozygous normal noncarriers.

Threshold Effect

Caused by intermediate level of gene expression where a certain level (usually 50% or less) of gene product is attained, resulting in normal phenotypic expression.

Codominance

No dominance or recessiveness. No incomplete or blending. Joint expression of both alleles in a heterozygote.

Multiple Alleles

Three or more alleles of the same gene; Resulting mode of inheritance unique; Can only be studied in populations.

Bombay phenotype

Phenotypically type O female, yet one parent has type AB blood and female is IB allele donor to two children.

Essential genes

Absolutely required for survival; Mutations can be tolerated if heterozygous; Homozygous recessive will not survive.

Dominant lethal allele

Presence of one copy of allele results in death.

Epistasis

Expression of one gene masks/modifies effect of another gene pair.

Epistasis

First locus produces product which is epistatic to second locus; Second locus is hypostatic to the first locus

Bombay phenotype (epistasis example)

Homozygous recessive condition; First locus masks expression of second locus.

Complementation Analysis

Used to study individual mutations resulting in same phenotype; Can predict total number of genes determining a trait.

Complementation

Two mutations on two different genes; Homozygous recessive mutants in two different genes mate to create a wildtype phenotype.

Complementation group

All mutations present in any single gene; Mating of two mutants does not create wild type.

Pleiotropy

Expression of single gene has multiple phenotypic effects.

Sex Determination (Drosophila and humans)

Males: XY; Females: XX

X-linkage

Genes present on X chromosome exhibit patterns of inheritance; Different from autosomal genes.

Sex-limited inheritance

Expression of specific phenotype is absolutely limited to one sex.

Sex-influenced inheritance

Sex of individual influences expression of phenotype; Not limited to one sex or the other.

Penetrance

Percentage of expression of the mutant genotype in a population.

Expressivity

Range of expression of mutant phenotype; Result of genetic background differences and/or environmental effects.

Position effect

Physical location of gene influences expression; Translocation or inversion events modify expression; Can get moved to an area of high or low expression (heterochromatin).

Conditional mutation

Phenotypic condition determined by the environmental conditions.