Topic 4 Terms

true-breeding

A genetic line in which self-crossing (or in animals, crossing within the line) always produces offspring with the same phenotype

Function: Provides consistent parental strains for genetics crosses and demonstrates homozygosity.

character

A heritable feature or property of an organism (e.g., coat color in mice)

Function: Serves as the unit of study in Mendelian inheritance experiments.

trait

A specific observable form of a character (e.g., black vs brown coat color)

Function: Used to distinguish alternative phenotypic outcomes of a single gene

phenotype

The observable physical or biochemical expression of a genotype

Function: Basis for tracking inheritance patterns and testing genetic hypotheses

genetic cross

A mating between two organisms to study inheritance patterns

Function: Reveals how traits are transmitted across generations.

intercross

A mating between F1 individuals; in plants often a self-cross, in animals a mating between F1 male and female.

Function: Produces the F2 generation, allowing observation of Mendelian ratios.

monohybrid cross

A cross involving variation in a single character.

Function: Demonstrates segregation of alleles and Mendel’s first three laws.

Parental Generation (P1)

The original true-breeding parents used in a genetic cross.

Function: Provides the starting point for study inheritance

F1 (First Filial) Generation

The offspring resulting from a P1 cross; heterozygous at differing loci.

Function: Used to test dominance relationships and serve as parents for the F2

hybrid

An organism produced by crossing parents with different traits.

Function: Reveals dominance, recessiveness and allele interactions.

F2 generation

The offspring of an intercross of F1 individuals.

Function: Reveals Mendelian rations (e.g., 3:1 phenotype) confirming segregation.

gene

A unit of heredity that affects phenotype.

Function: Encodes genetic instructions that influence traits

dominance

A relationship in which one allele masks the expression of another in the heterozygote.

Function: Explains why certain traits appear in hybrids

dominant

The allele whose trait is expressed in the heterozygote.

Function: Determines visible phenotype in presence of a recessive allele

recessiveness

A relationship where an allele’s trait is hidden by a dominant allele in heterozygotes.

Function: Explains reappearance of traits in F2 after skipping F1.

recessive

An allele whose trait is masked in the hererozygote and expressed only when homozygous.

Function: Contributes hidden genetic variation passed across generations.

segregation

The separation of the two alleles of a gene during gamete formation in meiosis.

Function: Ensures each gamete carries only one allele per gene.

gamete

Haploid reproductive cell (sperm or egg) that carries one allele of each gene

Function: Combines at fertilization to restore diploid state and transmit alleles.

allele

An alternative form of a gene (e.g., B for black, b for brown)

Function: Provides variation in traits within a population

homozygous

Having two identical alleles for a gene (e.g., BB or bb)

Function: Produces true-breeding lines and consistent phenotypes

heterozygous

Having two different alleles for a gene (e.g., Bb)

Function: Displays dominance/recessiveness relationships.

genotype

The genetic makeup of an organism (the specific alleles it carries)

Function: Determines potential phenotypes and inheritance patterns

testcross (Aka back cross)

A cross of an F1 individual back to a parental line, often the recessive one to determine the unknown genotype.

Function: Identifies whether a dominant-phenotype individual is homozygous or heterozygous

Punnett square

A grid used to predict the outcome of genetic crosses by combining gametes.

Function: Provides a visual representation of expected genotypic and phenotypic rations.

multiple alleles

More than two allelic forms of a gene exist in the population.

Function: Expands trait diversity beyond simple dominant/recessive patterns (e.g., coat color alleles in guinea pigs)

incomplete domiance

A relationship where the heterozygote’s phenotype is intermediate between the two homozygotes.

Function: Produces blended traits (e.g., red x white snapdragons → pink)

codominance

A relationship where the heterozygote expresses both homozygous phenotypes simultaneously.

Function: Creates phenotypes with both traits visible (e.g., AB blood type)