#3 Traits and the relationship between genetic and phenotypic variation

What is a genotype?

The genetic makeup of an organism; the set of genes it carries.

What is a phenotype?

The observable traits of an organism, produced by the interaction of genotype and environment.

How does genetic variation differ from phenotypic variation in a population?

• Genetic variation = differences in genes among individuals

• Phenotypic variation = differences in observable traits, influenced by both genes and environment

What is microevolution?

Evolutionary change in allele frequencies within a population over generations.

What is macroevolution?

Evolutionary change at or above the species level, including speciation and large-scale patterns.

At what level do most evolutionary processes occur?

The population level (microevolution)

What is the dual role of genes in biology?

• Genes determine traits within an organism

• Genes are inherited units passed across generations, allowing evolution

Why are genes (not other cell parts) the key contribution parents make to offspring in evolution?

Because genes are heritable, replicate accurately, and are passed to offspring, allowing natural selection to act.

What is the difference between a discrete and a continuous trait?

• Discrete: distinct categories (e.g., blood type)

• Continuous: range of values (e.g., height)

Give an example of a discrete trait.

Blood type, presence/absence of a structure, larval color morphs.

Give an example of a continuous trait.

Height, body mass, skin pigmentation.

What is the difference between an obligate and a facultative trait?

• Obligate: trait expressed regardless of environment

• Facultative: trait depends on environmental conditions

What does a reaction norm show?

How a genotype’s phenotype changes across different environments.

How can you tell if a trait is facultative from its reaction norm?

If phenotype changes across environments, the trait is facultative.

What about the Nemoria larval phenotype shows it is a discrete facultative trait?

Larvae develop into one of two distinct forms depending on diet, showing discrete outcomes controlled by environment.

Give an example of a trait where reaction norms differ between genotypes.

Plant height or growth rate where different genotypes respond differently to nutrient or light availability.

Macroevolution

Evolution at or above the species level, including speciation.

Microevolution

Evolutionary change in allele frequencies within populations.

Genotype

An organism’s genetic makeup.

Phenotype

Observable traits resulting from genotype × environment.

Discrete trait

Trait with distinct, separate categories.

Continuous trait

Trait with a continuous range of values.

Obligate trait

Trait expressed regardless of environmental conditions.

Facultative trait

Trait whose expression depends on the environment.

Reaction norm

Pattern of phenotypic expression of a genotype across environments.

Phenotypic plasticity

Ability of one genotype to produce different phenotypes in different environments.

Genetic variation

Differences in genes among individuals in a population.

Phenotypic variation

Differences in observable traits among individuals.