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4.7: End of Chapter Content

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    For Further Exploration

    Explore Evolution on HHMI’s Biointeractive website.

    Teaching Evolution through Human Examples, Smithsonian Museum of Natural History websites.


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    Many thanks to Dr. Vincent M. Riccardi for sharing his vast knowledge of neurofibromatosis and for encouraging me to explore it from an anthropological perspective.

    Image Descriptions

    Figure 4.1: The universal ancestor (left) is depicted as a blue capsule with two tails. From it, lines branch right indicating the evolution of bacteria (top), archaea (middle), and eukarya (bottom). The bacteria branch notes “photosynthesis” and “respiration.” Archaea and Eukarya share “ribosomal RNA changed by mutation” before splitting into their two branches. The Eukarya branch also notes “nucleus and membranous organelles” and “respiration” before diverging into five separate branches with respective images of a mouse, mushroom, parasite, green algae, and a fern frond. Multicellularity is noted as independently evolving on the mouse, mushroom, and fern branches.

    Figure 4.2: Snapdragons are used to illustrate phenotypes, genotypes, and alleles in a three part diagram.

    Top diagram

    At the top, three snapdragons are each labeled with a pair of letters:

    • Red snapdragon – Two uppercase Rs
    • Pink snapdragon – One upper case R and one lower case r
    • White snapdragon – Two lower case rs

    The set of three has two labels:

    • phenotype (flower color)
    • genotype (pair of alleles)

    Middle diagram

    A rectangle labeled “population (gene pool)” contains ten different snapdragons with corresponding genotypes: four red snapdragons (two uppercase Rs), four pink (one upper case R, one lower case r), and two white (two lower case rs).

    Text on the side reads:

    • Genotype frequencies (How often we note each combination: RR, Rr, or rr).
      • Freq. of RR = 4/10 = 0.4
      • Freq. of Rr = 4/10 = 0.4
      • Freq. of rr = 2/10 = 0.2
    • Allele frequencies (How often we see each allele: R or r
      • Freq. of R = 12/20 = 0.6
      • Freq. of r = 8/20 = 0.4

    Bottom diagram

    Three circles, connected by arrows, each surround a population of five snapdragons with their genotype labels (two letters for each snapdragon). A label reads: Allele frequency change is population evolution. Underneath each population is the corresponding allele frequencies.

    • First population contains three red (RR), one pink (Rr), and one white (rr) snapdragons.
      • Freq. R = 7/10 = 0.7
      • Freq. r = 3/10 = 0.3
    • Second population contains one red (RR), three pink (Rr), and one white (rr) snapdragons.
      • Freq. R = 5/10 = 0.5
      • Freq. r = 5/10 = 0.5
    • Third population contains one red (RR), two pink (Rr), and two white (rr) snapdragons.
      • Freq. R = 4/10 = 0.4
      • Freq. r = 6/10 = 0.6

    Figure 4.3: A capsule shaped universal ancestor is linked to a cell with smoothly rounded edges and different colored organelles by a thin black line. The line is labeled Eukarya branch (reminding the reader of Figure 4.1). Along the branch dots represent evolutionary events: ribosomal RNA changed by mutation, nucleus and membranous organelles, and respiration.

    Figure 4.4: Two DNA double helix shapes are drawn. The left one, labeled “Before” shows an arrow labeled “UV radiation” pointing towards its middle. The right one, labeled “After” bulges in the middle showing that the nucleotides on the same strand have bonded together, instead of to their complements on the other strand as they should.

    Figure 4.16: Three line graphs illustrate population change as a result of different types of selection. A blue line represents the original population, the red line represents the population after natural selection. While unlabeled, the X axis represents different phenotypes in the population, and the Y axis represents the frequency of each of those phenotypes. An image placed in the box of the line graph visualizes the trait being represented.

    Stabilizing selection

    Text reads: Robins typically lay four eggs, an example of stabilizing selection. Larger clutches may result in malnourished chicks, while smaller clutches may result in no viable offspring.

    Line graph indicates a narrower range of phenotypes – or many middle sized clutches – after selection on a population with more diverse clutch sizes. Image of eggs in a nest.

    Directional selection

    Text reads: Light-colored peppered moths are better camouflaged against a pristine environment; likewise dark-colored peppered moths are better camouflaged against sooty environments. Thus, as the Industrial Revolution progressed in nineteenth century England, the color of the moth population shifted from light to dark, an example of directional selection.

    Both the before and after population are bell-shaped curves, but the after population has shifted to the right indicating more dark-colored moths and few light-colored moths.

    Diversifying selection

    Text reads: In a hypothetical population, gray and Himalayan (gray and white) rabbits are better able to blend with a rocky environment than white rabbits, resulting in diversifying selection.

    Image shows the before population as a bell-shaped curve with white rabbits (in the middle) as the most common. The after population shows more gray and Himalayan rabbits (the extremes on each side) as more populous than the white rabbit in the middle.

    This page titled 4.7: End of Chapter Content is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Andrea J. Alveshere (Society for Anthropology in Community Colleges) via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.