Natural Selection — Flashcards & Quiz

Q1: Outline Darwin's theory of natural selection.

Natural selection requires: 1) Variation — individuals differ in heritable traits. 2) Overproduction — more offspring are produced than can survive. 3) Competition — resources are limited, creating a struggle for survival. 4) Differential survival and reproduction — individuals with advantageous traits are more likely to survive and reproduce. 5) Inheritance — advantageous traits are passed to offspring, increasing their frequency in the population over generations.

Q2: Compare stabilising, directional and disruptive selection.

Stabilising selection: favours the intermediate phenotype, reducing variation (e.g. human birth weight — very small or very large babies have lower survival). Directional selection: favours one extreme phenotype, shifting the population mean (e.g. antibiotic resistance in bacteria). Disruptive selection: favours both extreme phenotypes over the intermediate, potentially leading to speciation (e.g. beak sizes for different seed types).

Q1: Natural selection acts on the phenotype of an individual, not directly on the genotype.

Answer: TRUE

Natural selection acts on observable traits (phenotype) that affect survival and reproduction. Genotype is inherited, but selection pressure is exerted through the phenotype expressed.

Q2: Organisms deliberately develop beneficial mutations in response to environmental changes.

Answer: FALSE

Mutations are random and not directed by environmental need. Natural selection then favours individuals who happen to have beneficial mutations — the mutations pre-exist, they are not caused by the environment.

Q3: Directional selection favours one extreme phenotype, shifting the population mean in one direction.

Answer: TRUE

Directional selection favours individuals at one end of the phenotypic range, causing the population mean to shift towards that extreme over generations (e.g. increasing antibiotic resistance).