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Unit 18: Evolution

Last updated

May 14, 2022
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- 17.4C: Biological Control of Pests
- 18.1: Evolution and Adaptation

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18.1: Evolution and Adaptation
This page summarizes key concepts of evolution introduced by Charles Darwin in "The Origin of Species," focusing on adaptation, natural selection, and speciation. It highlights various selection types, including stabilizing, directional, and disruptive selection, as well as examples like finch beak size related to gene expression and the peppered moth's adaptation to pollution.
18.2: Speciation
This page explores the definition of species as interbreeding populations and the processes of speciation, including geographical isolation and adaptive radiation, exemplified by Darwin's finches. It discusses hybridization and various speciation types, such as allopatric and sympatric, with examples from plants and animals.
18.3: The Evolution of Body Form in Animals
This page explores the paradox of structural diversity and genetic similarity in the animal kingdom, emphasizing the role of mutations in gene regulatory regions that differentiate species, particularly in humans and chimpanzees. Research on a Tc1 mouse carrying human chromosome #21 reveals that most human genes function similarly in mouse cells. While housekeeping and toolkit genes are conserved, species diversity arises from changes in DNA sequences affecting gene expression.
18.4: Recapitulation
This page discusses the similarities in vertebrate embryonic development, particularly during the pharyngula stage, where key structures appear. It introduces the recapitulation theory, which posits that early developmental stages mirror ancestral forms, despite variations among species. The page notes that while embryos exhibit analogous features like limb bud formation, many are lost or altered later.
18.5: Mutation and Evolution
This page discusses the role of mutations in evolution, noting that while many mutations are harmful or neutral, gene duplication provides opportunities for advantageous changes. It highlights the impact of regulatory region mutations on gene expression, using the Pitx1 gene in sticklebacks as an example.
18.6: The Hardy-Weinberg Equilibrium
This page explains how various mechanisms, such as assortative mating and natural selection, disrupt Hardy-Weinberg equilibrium, leading to changes in allele frequencies within populations. It highlights the impact of preference for similar phenotypes on genetic diversity and the role of natural selection in promoting beneficial traits.
18.7: Polymorphisms
This page discusses genetic polymorphisms, which are variants found in at least 1% of a population and include different types of genetic variations. These polymorphisms have applications in disease identification and genetic studies and can be influenced by factors like genetic drift and natural selection.
18.8: Kin Selection
This page discusses kin selection and altruism in evolution, highlighting self-sacrificing behaviors like those of honeybee workers and protective birds. It posits that such actions enhance the inclusive fitness of related individuals by promoting the survival of shared genes.
18.9: The Origin of Life
This page explores the origin and evolution of life, detailing theories on the formation of organic molecules and cellular systems. It highlights key milestones such as Miller's amino acid synthesis, the RNA world hypothesis, and the transition from unicellular to multicellular organisms, exemplified by Gonium and Volvox. The concept of the Last Universal Common Ancestor is addressed.
18.10: Mars
This page discusses NASA's Viking missions, which sought evidence of life on Mars in 1976 but found none conclusively. The ambiguous results of the Labeled-Release and Gas-Exchange experiments were later linked to nonbiological processes. Although the Curiosity rover discovered organic compounds and Martian meteorites like ALH84001 contain organic molecules, the potential for contamination complicates the findings.
18.11: Endosymbiosis
This page explores the endosymbiosis theory, which suggests that eukaryotic mitochondria and chloroplasts originated from engulfed bacteria. Mitochondria contain 37 essential genes, while chloroplasts have 128, including those for photosynthesis. It also discusses the complex genomic relationships in some protists, particularly the chloroplast and apicoplast, the latter being crucial for apicomplexan survival. The apicoplast has a limited genome and requires proteins from the host's nucleus.
18.12: Geologic Eras
This page outlines the fossil record's portrayal of life's history through geological eras, emphasizing significant events like mass extinctions driven by asteroid impacts, exemplified by the Alvarez theory and iridium layers. It discusses the influence of continental drift on species distribution and highlights key extinctions, including the Triassic and Permian extinctions, linking them to catastrophic events. These factors collectively have shaped the evolutionary trajectory of life on Earth.

Thumbnail: A silhouette of human evolution. (CC BY SA 3.0 Unported; Tkgd2007).

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