Genetics: Key Concepts and Inheritance Patterns

Inheritance

The passing of traits from parents to offspring

Blending inheritance

Incorrect idea that traits mix together permanently

Particulate inheritance

Correct idea that traits are controlled by discrete units that remain intact

Gene

A unit of inheritance that affects a trait

Allele

Different versions of the same gene

Character

An observable feature (e.g., seed shape)

Trait

A specific form of a character (e.g., round or wrinkled)

True-breeding

Organisms that always produce offspring with the same trait when self-fertilized

P generation

The parental generation

F1 generation

Offspring of the P generation

F2 generation

Offspring of the F1 generation

Dominant trait

Trait that appears in the heterozygote and masks the recessive allele

Recessive trait

Trait masked by a dominant allele; appears only when two recessive alleles are present

Genotype

The genetic makeup of an organism (e.g., RR, Rr, rr)

Phenotype

The physical expression of a trait

Diploid

Having two copies of each gene

Haploid

Having one copy of each gene (gametes)

Law of Segregation

Allele pairs separate during gamete formation

Meiosis

Cell division process that produces gametes and explains segregation

Law of Independent Assortment

Alleles of different genes assort independently if on different chromosomes

Punnett square

A diagram used to predict offspring genotypes and phenotypes

Multiplication rule

Calculates probability of independent events occurring together

Addition rule

Calculates probability of events that can occur in multiple ways

Monohybrid cross

A cross examining one character

Dihybrid cross

A cross examining two characters

Pedigree

A family tree showing inheritance of traits

Carrier

An individual with one recessive allele who does not show the trait

Mutation

A rare, heritable change in DNA

Wild-type allele

The most common allele in a population

Mutant allele

An alternative form of a gene

Polymorphic gene

A gene with multiple alleles where no single allele exceeds 99% frequency

Multiple alleles

More than two alleles exist for a gene in a population

Incomplete dominance

Neither allele is fully dominant; heterozygote has intermediate phenotype

Codominance

Both alleles are fully expressed in a heterozygote

Epistasis

One gene affects the expression of another gene

Hybrid vigor (heterosis)

When hybrid offspring show superior traits compared to parents

Gene-environment interaction

When environmental conditions affect gene expression

Penetrance

Percentage of individuals with a genotype who show the phenotype

Expressivity

Degree to which a genotype is expressed in an individual

Heritability

Measure of how much variation in a trait is due to genetics (ranges from 0-1; applies to populations)