Darwin’s Explanation for Darwin’s Explanation for EvolutionEvolution

• 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

What Were The Two Ideas What Were The Two Ideas Lacking in Darwin’s Natural Lacking in Darwin’s Natural

Selection Theory?Selection Theory?

• Source of variationSource of variation

• How traits are inheritedHow traits are inherited

Who Solved These Who Solved These Problems?Problems?

• How traits are inherited: How traits are inherited: MENDELMENDEL– Two “Particle”s for every trait;

Segregation; Independent Assortment; Dominance & Recessive

• Ultimate source of variations: Ultimate source of variations: DeVRIESDeVRIES – Mutations

Tao of MendelTao 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.

Tao of MendelTao 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

Tao of MendelTao of MendelLaw of SegregationLaw of Segregation

• For every trait an organism has, it has For every trait an organism has, it has two “particles” (aka alleles) for that two “particles” (aka alleles) for that trait: one from one parent, the other trait: one from one parent, the other from the other parentfrom the other parent

2 alleles per trait2 alleles per trait

• During gamete formation, the paired During gamete formation, the paired alleles alleles SEGREGATESEGREGATE, with one allele , with one allele going into one sex cell and the other going into one sex cell and the other allele going into a allele going into a different sex celldifferent sex cell

Tao of MendelTao of MendelLaw of Independent Law of Independent

AssortmentAssortment

• Distribution into sex cells of alleles for Distribution into sex cells of alleles for one trait (e.g. earlobe attachment) is one trait (e.g. earlobe attachment) is unrelatedunrelated to how alleles for a different to how alleles for a different trait (e.g. blood type) segregate and are trait (e.g. blood type) segregate and are distributed into the sex cells.distributed into the sex cells.– AB, Rr: a person’s genotypeAB, Rr: a person’s genotype– Same person’s sex cell components:Same person’s sex cell components:

• AR, Ar, BR, BrAR, Ar, BR, Br

Note: this law only valid IF alleles for one trait are on a differentchromosome (i.e., DNA strand)