Lecture 3: The Evolutionary Significance of Genetic Variation

Flashcards covering key vocabulary, definitions, mechanisms, and historical frameworks for genetic variation, inheritance, mutation rates, and evolutionary synthesis from Lecture 3.

Genotype

The genetic constitution of an organism, defined in relation to a particular gene or gene combination, specifying both alleles of a gene locus in diploid organisms.

Phenotype

An observed feature or trait of an organism that varies, such as size, fur color, enzyme activity, or mRNA expression level.

Genome

The entirety of an organism's DNA, including coding genes and non-coding regions, as well as distinct organelle genomes in mitochondria and chloroplasts.

Mutation

A stable change in the DNA sequence that is inevitable, rare, non-directed toward an outcome, and random with respect to its effect on fitness.

Point Mutation

A type of mutation involving a single base substitution within a DNA sequence (e.g., ATGCAGT changing to ATCCAGT).

Indel

An insertion or deletion of nucleobases within a DNA sequence (e.g., ATGCAGT changing to ATGGCAGT).

Chromosomal Rearrangement

A structural alteration of a chromosome, such as an inversion (e.g., AATGCAGTT changing to ATGACGTAT).

Human Mutation Rate

Approximately $0.000000016$ (16 in every billion nucleotides) per base pair per generation, yielding approximately 96 new mutations per zygote.

G6PD Deficiency

The most common enzyme deficiency in humans, caused by 2 amino acid replacement mutations; the disease allele ($A-$) causes severe anemia while providing resistance against malaria.

Independent Assortment

The random segregation and distribution of homologous chromosome sets into gametes during meiosis, creating new allele combinations in offspring.

Recombination

The exchange of genetic material between non-sister chromatids of homologous chromosomes during meiosis via crossing over at chiasmata.

Theory of Blending Inheritance

An 1800s hypothesis postulating that hereditary factors from both parents mix together irreversibly, which posed a problem for natural selection by diluting new mutations across generations.

Gregor Mendel

The scientist (1822–1884) who established the principles of particulate inheritance through hybridization experiments on seven discrete traits in pea plants.

Particulate Inheritance

The mechanism of heredity where traits are passed to offspring through discrete, persistent units (genes) that retain their integrity rather than blending.

Discrete Trait

A trait governed by simple Mendelian genetics that falls into distinct, non-overlapping phenotypic categories (e.g., purple vs. white flower color).

Quantitative Trait

A complex trait showing continuous phenotypic variation across a spectrum (e.g., human height), influenced by many polygenic loci of small effect and environmental factors.

The Evolutionary Synthesis

The scientific unification established by R.A. Fisher, J.B.S. Haldane, and S. Wright, demonstrating that continuous phenotypic variation and Darwinian natural selection are fully consistent with Mendel's laws.

Ophioglossum petiolatum

A species of fern with 510 sets of chromosomes capable of generating $2^{510} \times 3.4 \times 10^{153}$ unique gamete combinations through independent assortment.

Bacteriophage \Phi X174

A virus used in experimental evolution studies (Domingo-Calap et al. 2009) to quantify the distribution of fitness effects across 45 induced mutations relative to an ancestral strain.