The Making of the Fittest: The Birth and Death of Genes (Video Transcript)

Vocabulary flashcards covering key concepts from the lecture transcript, including Notothenioid antifreeze evolution, gene evolution, gas exchange, homeostasis, and phylogeny/speciation.

icefish (Notothenioids)

Antarctic group of fishes; notable for antifreeze proteins and, in icefish, absence of red blood cells and hemoglobin allowing survival in near-freezing seawater.

antifreeze protein (AFP)

A protein that binds ice crystals to prevent growth, enabling Notothenioids to invade and thrive in freezing Antarctic waters.

Notothenioids

Antarctic fish group that includes icefish; evolved antifreeze protection and, in some species, loss of hemoglobin.

hemoglobin

Oxygen-carrying protein in red blood cells; icefish lack functional hemoglobin.

icefish blood

Blood without red blood cells or hemoglobin, enabled by antifreeze adaptation and uptake of dissolved oxygen through skin.

gill lamellae

Thin folds on gill filaments where gas exchange occurs; reduce diffusion distance in fish.

countercurrent exchange

A mechanism where blood and water flow in opposite directions along exchange surfaces to maximize oxygen uptake.

concurrent flow

Exchange arrangement where blood and water flow in the same direction; less efficient than countercurrent flow.

Fick’s law of diffusion

Q = (D × A × (P1 − P2)) / L; describes how diffusion rate depends on diffusion coefficient, surface area, partial pressure difference, and diffusion distance.

partial pressure

Pressure exerted by a gas component in a mixture; drives diffusion of gases like O2 and CO2.

Oxygen dissociation curve

Graph of hemoglobin saturation vs. PO2 showing Hb affinity for O2 under different conditions.

Bohr effect

Lower blood pH (higher CO2) reduces hemoglobin’s oxygen affinity, promoting O2 release in tissues.

left shift (O2 affinity)

Higher Hb affinity for O2 (less CO2, higher pH, lower temperature) shifting the curve to the left.

right shift (O2 affinity)

Lower Hb affinity for O2 (more CO2, lower pH, higher temperature) shifting the curve to the right.

hemoglobin affinity

Tendency of Hb to bind or release O2; influenced by pH, CO2, temperature, and 2,3-BPG in mammals.

antifreeze genes

Genes that encode antifreeze proteins; in Notothenioids these originated via gene duplication and divergence.

gene duplication

Copying of a gene in the genome; a major source of genetic novelty and raw material for evolution.

neofunctionalization

Duplicated gene evolves a new function distinct from the original gene.

subfunctionalization

Duplication leads to partitioning of the original gene’s functions between copies.

de novo gene origination

New genes arising from previously noncoding DNA sequences.

pseudogene

A nonfunctional gene copy or vestige, often arising from duplication or retrotransposition.

endosymbiosis

One organism living inside another; origins of mitochondria/chloroplasts and their gene transfers.

horizontal (lateral) gene transfer

Movement of genetic material between organisms not parent-offspring (e.g., bacteria to bacteria; organelle to nucleus).

polyploidy

Cell/organism with more than two complete chromosome sets; includes autopolyploidy and allopolyploidy.

autopolyploidy

Polyploidy resulting from chromosome duplication within a single species.

allopolyploidy

Polyploidy arising from hybridization between two species followed by chromosome doubling.

prezygotic barriers

Barriers preventing mating or fertilization before zygote formation (habitat, temporal, behavioral, mechanical, gametic isolation).

postzygotic barriers

Barriers after fertilization that reduce viability or reproduction of hybrids (hybrid inviability, infertility, breakdown).

allopatric speciation

Speciation due to geographic isolation (vicariance or dispersal) separating populations.

vicariance

Geographic splitting of a population’s range, leading to isolation and speciation.

dispersal

Movement of individuals to new areas, initiating geographic isolation and speciation.

sympatric speciation

Speciation without geographic separation; divergence due to other isolating mechanisms.

lineage (phylogenetic) species concept

Species as branches on the tree of life; emphasizes evolutionary history and ancestry.

morphological species concept

Species defined by distinctive physical traits and appearance.

biological species concept

Species as reproductively isolated groups that can interbreed in nature.

clade/monophyletic group

A group consisting of an ancestor and all its descendants; a single complete branch on the tree of life.

homologous traits

Traits shared by species due to common ancestry; can be structurally different though functionally similar.

analogous traits

Traits that are similar due to convergent evolution, not shared ancestry.

convergent evolution

Independent evolution of similar traits in unrelated lineages due to similar pressures.

molecular clock

Hypothesis that genetic sequences evolve at a relatively constant rate over time, used to estimate divergence times.

calibration (molecular clock)

Using independent data (fossils, known divergences) to convert molecular change into time.

synonymous (S) substitutions

DNA substitutions that do not change the encoded amino acid; usually neutral.

nonsynonymous (N) substitutions

DNA substitutions that change the encoded amino acid; can affect fitness.

N/S ratio (dN/dS)

Ratio of nonsynonymous to synonymous substitutions; >1 indicates positive selection, <1 indicates purifying selection, ≈1 neutral.

skin color as a polygenic trait

Characteristic influenced by many genes; variation in skin pigmentation is controlled by multiple genes.

folate and UV trade-off

Melanin/light skin vs UV exposure: folate preservation vs vitamin D production; balanced by latitude-driven selection.