Transmission Genetics – Core Vocabulary

Flashcards summarizing the fundamental vocabulary introduced in the lecture notes on Mendelian transmission genetics.

Phenotype

The observable traits or characteristics of an organism, such as seed shape or flower color.

Genotype

The genetic makeup of an organism—the specific alleles it carries at a gene or set of genes.

Allele

One of two or more alternative forms of a gene found at the same locus.

Homozygous

Having two identical alleles for a given gene (e.g., WW or ww).

Heterozygous

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

Dominant allele

An allele that masks the phenotypic effect of a recessive allele in heterozygotes.

Recessive allele

An allele whose phenotypic effect is expressed only in homozygous form.

Codominance

A relationship in which both alleles in a heterozygote are fully and simultaneously expressed (e.g., IAIB blood type).

Incomplete dominance

A relationship in which the heterozygote shows an intermediate phenotype between the two homozygotes (e.g., pink snapdragons).

Molecular phenotype

A trait detected at the DNA or protein level, such as a band on an electrophoretic gel.

Morphological phenotype

A trait visible at the organismal level, such as seed color or stem length.

Segregation (Mendel’s First Law)

The two alleles of a gene separate during gamete formation so each gamete receives only one allele.

Independent assortment (Mendel’s Second Law)

Allele pairs of different genes segregate into gametes independently of one another.

Punnett square

A grid used to predict the genotype and phenotype ratios resulting from a genetic cross.

Monohybrid cross

A cross between parents that differ in a single gene or trait.

Dihybrid cross

A cross between parents that differ in two genes; F₂ phenotypes often follow a 9 : 3 : 3 : 1 ratio.

Trihybrid cross

A cross tracking three independently assorting genes; F₂ phenotypes can follow a 27 : 9 : 9 : 9 : 3 : 3 : 3 : 1 pattern.

Testcross

A cross between an individual of unknown genotype and a homozygous recessive to reveal the unknown genotype.

Backcross

A cross between a hybrid organism and one of its parental genotypes.

Reciprocal cross

Two crosses in which the male and female parents are swapped to test if inheritance is sex-dependent.

True-breeding

Describes a strain that produces offspring identical to itself for a trait when self-fertilized.

Hybrid

The offspring of a cross between parents differing in one or more traits; e.g., F₁ generation.

Gamete

A haploid reproductive cell—sperm or egg—that carries one allele of each gene.

Transmission genetics

The branch of genetics that studies how genes are passed from parents to offspring.

Epistasis

Interaction in which one gene masks or modifies the expression of another, altering Mendelian ratios (e.g., 9 : 7).

Multiple alleles

The presence of more than two allelic forms of a gene within a population.

Penetrance

The proportion of individuals with a genotype who actually express the associated phenotype.

Pedigree

A family tree diagram showing the inheritance of traits across generations.

Complementation test

Crossing two recessive mutants to determine if they affect the same gene (non-complementation) or different genes (complementation).

Complementation group

A set of mutations that fail to complement each other; operational definition of a gene.

Noncomplementation

When two mutations in a cross fail to restore the wildtype phenotype, indicating alleles of the same gene.

Mutant screen

A systematic search for new mutations affecting a trait of interest.

Wildtype

The most common or standard allele or phenotype found in natural populations.

RFLP (Restriction Fragment Length Polymorphism)

DNA variation detected by differing fragment sizes after restriction enzyme digestion.

RAPD (Random Amplified Polymorphic DNA)

A PCR-based technique that amplifies random genomic regions to reveal polymorphic bands.

SNP (Single-Nucleotide Polymorphism)

A variation at a single base pair in DNA; occurs roughly every 500–3000 bp in humans.

STRP (Simple Tandem Repeat Polymorphism)

A polymorphism based on variable numbers of short tandem repeats (also called microsatellites).

Transposable element

A DNA sequence capable of moving to new positions within the genome; can interrupt genes and cause mutations.

Amylopectin

A branched starch whose absence leads to wrinkled pea seeds.

Starch-branching enzyme I (SBEI)

Enzyme that synthesizes amylopectin; inactive in wrinkled-seed peas due to a transposon insertion.

Round vs. wrinkled seed phenotype

Classic Mendelian trait in peas controlled by the SBEI gene—W (round) is dominant to w (wrinkled).

Codominant molecular marker

A marker where heterozygotes show both parental bands, allowing direct genotype identification.

Principle of segregation

Each gamete receives one allele of each gene; alleles separate unchanged during gamete formation.

Principle of independent assortment

Alleles of different genes segregate into gametes independently when genes are unlinked.

Consanguineous mating

A mating between related individuals; often denoted by a double line in pedigrees.

Carrier

An individual heterozygous for a recessive allele who is phenotypically normal but can transmit the allele.

Antigen

A molecule that can provoke an immune response and be recognized by antibodies (e.g., A and B blood-group sugars).

Antibody

A protein produced by the immune system that specifically binds an antigen; can agglutinate mismatched blood cells.

Universal donor

Blood-type O individual whose red cells lack A and B antigens and can be transfused to any ABO type.

Universal recipient

Blood-type AB individual who lacks anti-A and anti-B antibodies and can receive blood from any ABO type.