Genetics, Evolution, and Paleontology: Key Concepts and Definitions

Genome

Entire set of genes and nucleotides in an organism, stored in chromosomes (DNA + protein scaffold).

Synonymous substitution

Mutation that does not change amino acid; neutral.

Nonsynonymous substitution

Mutation that changes amino acid; potentially harmful.

Kimura's Neutral Theory

Most mutations arise from random molecular events, not natural selection.

Mutation types

Point mutation, insertion, deletion, duplication, inversion, translocation.

Positive selection

Favors beneficial alleles.

Purifying selection

Removes harmful alleles.

Balancing selection

Maintains multiple alleles.

Pseudogene

Former functional gene that became nonfunctional after duplication.

Gene family

Group of related genes from duplication (e.g., hemoglobin/myoglobin).

Nonfunctional DNA roles

Structural or protective roles (e.g., telomeres, centromeres).

Hox genes

Regulatory genes controlling segmentation & body plan development.

Species

Group of interbreeding organisms producing fertile offspring.

Morphological species concept

Based on physical traits; simple but subjective.

Biological species concept

Based on reproductive isolation; doesn't apply to fossils/asexuals.

Lineage (Phylogenetic) species concept

Based on shared evolutionary history; may split species too finely.

Speciation result

Two reproductively isolated lineages.

Dobzhansky-Muller Model

Populations diverge → mutations become fixed (permanent).

Hybrid incompatibility

Different alleles in each lineage cause hybrid incompatibility when combined.

Allopatric speciation

Physical barrier divides population → genetic drift + founder effect.

Founder effect

Small isolated population evolves differently.

Ring species

Adjacent populations interbreed, distant ones can't.

Sympatric speciation

No physical barrier; often caused by polyploidy or niche shifts.

Autopolyploidy

Doubling of own chromosomes.

Allopolyploidy

Chromosome doubling after hybridization between species.

Prezygotic mechanisms

Prevent mating/fertilization.

Postzygotic mechanisms

After fertilization mechanisms that reduce hybrid viability.

Continental drift

Movement of continents.

Subduction (Convergent)

Plates collide → one sinks.

Divergent

Plates move apart.

Transform fault

Plates slide past.

Lithosphere

Rigid crust.

Asthenosphere

Soft mantle layer below.

Milankovitch Cycles

Orbital changes that alter solar input → climate cycles.

Extinction

Environmental or biological collapse.

Allee Effect

Small populations struggle to survive due to low density.

Fossil

Preserved remains of organisms.

Biota

All life in an area.

Flora

Plants.

Fauna

Animals.

Ediacaran (~600 Ma)

Multicellular life.

Cambrian (542-488 Ma)

Cambrian explosion.

Ordovician (488-444 Ma)

Early sea animals.

Silurian (444-416 Ma)

Plants reach land.

Devonian (416-359 Ma)

Vertebrates move to land.

Carboniferous (359-299 Ma)

Swamps, oxygen-rich air.

Permian (299-251 Ma)

Reptiles dominate; mass extinction.

Prokaryote

No nucleus, circular DNA, binary fission.

Eukaryote

Nucleus, organelles.

Gram-positive

Thick peptidoglycan, purple stain.

Gram-negative

Thin peptidoglycan, outer membrane, pink stain.

Binary fission

Asexual reproduction by splitting.

Coccus

Spherical.

Bacillus

Rod-shaped.

Spirillum

Spiral.