Genes, Development, and Evolution: Chapter 21

Study Notes

Cell Differentiation: Early embryonic cells can become any cell type, specializing (differentiating) into specific types like neurons and muscle cells.
Mechanisms of Cell Fate: Cell fate is determined as molecules unequally distributed in daughter cells. One cell may receive a crucial signal the other does not.
Cell Death (Apoptosis): Programmed cell death is essential and regulates processes such as webbing between toes during embryonic development.
Body Plan Development: Cell fates depend on location along the anterior-posterior, dorsal-ventral, and left-right axes. Body plans are categorized, for instance, jellyfish and humans.
Pattern Formation: Cell differentiation is based on specified location, with disruption of gradients leading to developmental abnormalities.
Gene Regulatory Cascades: Genes dictate cell location and type.
Hox Genes: These genes specify body part identity and are conserved across animal species. They are crucial in development.
Development and Evolution: Evolutionary changes can arise through repurposing "tool-kit" genes. Constraints, such as genetic, physical, and chemical restrictions, limit evolutionary alterations.

Evolution: Populations evolve over time, not individuals. Evolution involves changes in population characteristics.
Genotype vs. Phenotype: Genotype is genetic information and Phenotype are the traits expressed.
Natural Selection: Individuals with favorable traits are more likely to reproduce and pass on those traits, driving evolutionary change.

Natural Selection: A non-random process favoring traits that lead to enhanced survival and reproduction.
- Types: Favoring one extreme of a phenotype or an intermediate phenotype or two extremes, and maintaining genetic variation.
Sexual Selection: Nonrandom mating based on traits, such as intersexual or intrasexual competition.
Genetic Drift: Random changes in allele frequencies, especially pronounced in smaller populations.
Gene Flow: Alleles moving between populations, increasing genetic diversity.
Mutation: Random DNA changes creating new alleles, the ultimate source of genetic variation.
Hardy-Weinberg Equilibrium: Predicts allele frequencies in a non-evolving population (no mutation, selection, or gene flow). A large population and random mating are crucial conditions.

Speciation: The formation of new species from ancestral species.
- Steps: Genetic isolation (barrier to gene flow) and genetic divergence (independent evolution).
Species Concepts: Species often defined by their ability to interbreed and produce fertile offspring.
Types of Speciation: Allopatric (different locations) and sympatric speciation (no difference in locations). Polyploidy in plants is a way to achieve sympatric speciation.
Hybrid Zones: Regions where two species interbreed, often producing hybrid offspring.

Phylogeny: The evolutionary history of an organism or group of organisms.
Tree Components: Phylogenies are depicted as branching trees with nodes representing common ancestors.
Clade: A group with a common ancestor and all of its descendants.
Homology vs. Homoplasy:
- Homology: Similarities due to common ancestry.
- Homoplasy: Similarities due to convergent evolution (similar traits independent of common ancestry).
Fossils: Fossils provide evidence about the history of life. Limitations of fossil records: habitat, taxonomic, and temporal bias.
Mass Extinctions: Sudden and significant declines in biodiversity.

Genes and Development: Hox genes control body development. Differentiation is based on cell signals.
Evolution: Natural selection alters populations over time.
Speciation: New species form via genetic isolation and divergence.
Phylogenies: Evolutionary relationships are illustrated by trees. Fossils provide evidence for the past.