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Understanding Darwin’s Evolutionary Theory and Mendelian Genetics

This comprehensive overview explores Darwin's theory of evolution, focusing on variations in phenotypes and genotypes, the struggle for existence, and the importance of limited resources. It highlights how natural selection favors certain traits relative to environmental conditions. Further, we delve into the missing links in Darwin's theory, particularly the sources of variation and inheritance as explained by Mendel's laws. We cover key concepts such as alleles, segregation, and independent assortment, illustrating how traits are passed from parents to offspring through genetic inheritance.

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Understanding Darwin’s Evolutionary Theory and Mendelian Genetics

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Presentation Transcript

  1. Darwin’s Explanation for Evolution • Not created equal (variations in phenotypes & genotypes) • Limited stuff (finite resources) • Produce more offspring than finite resources can support • Struggle for existence • Favorable vs. unfavorable traits (relative to the environment) • Inheritance

  2. What Were The Two Ideas Lacking in Darwin’s Natural Selection Theory? • Source of variation • How traits are inherited

  3. Who Solved These Problems? • How traits are inherited: MENDEL • Two “Particle”s for every trait; Segregation; Independent Assortment; Dominance & Recessive • Ultimate source of variations: DeVRIES • Mutations

  4. Tao of Mendel • Inheritance of each trait determined by ”particles" (alleles or genes) that pass on to descendents unchanged • An individual inherits one allele from each parent for each trait • A trait may not show up in an individual but can still be passed on to next generation.

  5. Tao of Mendel • Genes may be one of several types (ALLELES) • Earlobe attachment in humans: F (Free earlobe) or f (attached earlobe) • Blood type: A, B or o • Lutheran saliva protein: L1, L2, . . . L22 • Some alleles are DOMINANT: F (free earlobes) • Some alleles are recessive: f (attached earlobes) • and some are CO-DOMINANT: A and B blood alleles

  6. Tao of MendelLaw of Segregation • For every trait an organism has, it has two “particles” (aka alleles) for that trait: one from one parent, the other from the other parent 2 alleles per trait • During gamete formation, the paired alleles SEGREGATE, with one allele going into one sex cell and the other allele going into a different sex cell

  7. Tao of MendelLaw of Independent Assortment • Distribution into sex cells of alleles for one trait (e.g. earlobe attachment) is unrelated to how alleles for a different trait (e.g. blood type) segregate and are distributed into the sex cells. • AB, Rr: a person’s genotype • Same person’s sex cell components: • AR, Ar, BR, Br Note: this law only valid IF alleles for one trait are on a different chromosome (i.e., DNA strand)

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