MODULE 4: Genetic Variation & Phenotypes

Genetic variation

Differences in DNA sequences among individuals that create heritable differences in phenotype.

Environmental variation

Variation in phenotype caused by differences in environmental conditions rather than genetic differences.

Genotype-by-environment interaction (G×E)

When different genotypes respond differently to the same environment, causing performance rankings to change across environments.

Genome

The complete set of an individual's DNA.

Locus

The physical location of a gene on a chromosome.

Allele

A different version of a gene.

Do alleles need functional differences to be considered different?

No. Even synonymous sequence differences count as distinct alleles.

Genotype

The combination of alleles at one or more loci.

Phenotype

The suite of traits an individual exhibits; includes morphology, behavior, physiology, ecology, and sensory traits.

Univariate phenotype

A phenotype based on a single trait.

Multivariate phenotype

A phenotype that includes multiple traits together.

Example of phenotypic variation in sensory traits

Different alleles for bitter taste receptors create "sensitive," "insensitive," or intermediate taste phenotypes.

How can environment influence phenotype?

Environmental conditions (e.g., elevation, temperature, predators) can alter trait expression even with the same genotype.

Inducible defenses

Phenotypic traits expressed only when triggered by specific environmental cues such as predators.

Heat shock proteins (Hsp70)

A physiological response expressed under stress (e.g., high heat), showing environmental influence on phenotype.

What is G×E?

Not all genotypes react the same way to environmental change; the effect of environment depends on genotype.

Reaction norm

The range of phenotypes a single genotype can produce across different environmental conditions.

What does a reaction norm show?

How phenotype changes with environment for each genotype.

How do reaction norms illustrate G×E?

Different genotypes have different slopes or shapes of reaction norms, showing unequal responses to the same environment.

Phenotypic plasticity

The ability of a single genotype to produce different phenotypes in different environments.

Can plasticity vary genetically?

Yes. There can be genetic variation for the degree or type of plasticity expressed.

Relationship between reaction norms and plasticity

Reaction norms visualize phenotypic plasticity; plasticity produces the range of phenotypes shown in the reaction norm.