Speciation, Reproductive Isolation, and Molecular Evolution

Vocabulary and concept flashcards covering reproductive isolation, speciation mechanisms, geographic variation, genetic drift, and molecular evolution based on the lecture transcript.

Reproductive isolation

The lack of interbreeding between different species coexisting in the same locality, which serves as the primary criterion for defining distinct species.

Geographical variation

The tendency of local populations of the same species to differ in physical or genetic characteristics according to their geographic location, often in ways that are adaptive.

Migration (gene flow)

The movement of individuals between local populations of a species, which acts as a homogenizing force opposing genetic divergence caused by selection or genetic drift.

Inviability

A post-mating reproductive barrier where interspecies hybrid offspring fail to develop or die at an early stage of development.

Hybrid sterility

A post-mating reproductive barrier where hybrid offspring survive to adulthood but are unable to produce viable gametes or offspring, such as male hybrids between non-Bogotá and Bogotá Drosophila pseudoobscura.

Drosophila pseudoobscura (Bogotá population)

A geographically isolated population of fruitflies from Colombia that diverged approximately 200,000 years ago and produces sterile hybrid males when crossed with non-Bogotá females.

Mimulus lewisii

A bee-pollinated monkeyflower species with small, wide, pink flowers containing a landing platform and moderate nectar with high sugar content.

Mimulus cardinalis

A hummingbird-pollinated monkeyflower species with large, narrow, tubular red flowers and abundant nectar with low sugar content.

Floral characteristics of Mimulus species

A comparative summary showing how Mimulus lewisii and Mimulus cardinalis differ in pollinators, flower size, flower shape, flower colour, and nectar traits.

Replacement changes

Nucleotide substitutions in gene coding sequences that alter the corresponding amino acid sequence of the encoded protein.

Silent changes

Nucleotide substitutions in gene sequences that do not alter the amino acid sequence of the encoded protein.

Sequence differences in melanocyte-stimulating hormone receptor gene

A table comparing amino acid-altering (replacement) and non-altering (silent) gene differences between humans and chimpanzees (17 silent, 9 replacement), dogs (134 silent, 53 replacement), mice (169 silent, 63 replacement), and pigs (107 silent, 56 replacement).

Genetic drift

The process of continual random fluctuations in the frequencies of alternative gene copies over generations in finite populations, independent of natural selection.

Fixation

The outcome of genetic drift or selection when a particular gene variant spreads to reach a frequency of 100% in a population, replacing all alternative variants.

Molecular clock principle

The concept that selectively neutral sequence changes accumulate in genes over time at a rate determined by the neutral mutation rate per DNA letter.

Chronology of the tree of life

A set of phylogenetic trees depicting estimated divergence dates between major groups of organisms (all organisms, multicellular organisms, and birds/mammals) reconstructed using DNA sequence differences.