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Darwin’s Explanation for Evolution

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.

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Darwin’s Explanation for Evolution

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  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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