Variation and Natural Selection (Chap. 18). Two basic points of variation. Variation can occur in a wide array of traits (physical features, color, size....) We may not be aware of the variation (enzymes, disease susceptibility, blood type…). Variation comes from:. Sexual reproduction
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
·genetic recombination in meiosis continually produces variation by shuffling existing genes and alleles
·fertilization allows the alleles from two diff. individuals to be brought together in one new individual
·provides a steady input of new genes and alleles
Sickle Cell Video clip
a. The distribution of the falciparum malaria (Plasmodium falciparum) in the Old World before extensive eradication of mosquitoes begun in the '20s. b. The distribution of the sickle-cell allele within the same area. Intensity of color refers to increasing allele frequencies. Note the correlation between the two distributions.
The answer turned out to be yes. As the population of G. fortis recovered after the rains returned, the average body size and beak depth of their offspring was greater than before (an increase of 4–5% for beak depth). The bell-shaped curve had been shifted to the right — directional selection.