Gregor Mendel ( ) & the Foundations of Genetics

Change in one base pair - may or may not change amino acid, changed amino acid may or may not change protein conformation Spontaneous, but also increased by radiation, heat, chemical mutagens Rate ‘Infrequent’: one in a billion bases Mutation Point Mutations AATAAGAAAATATGAA

Three Point Mutations Substitution Insertion Deletion AATAAGAAAATAGAA AATAAGAAAATATGAA AATAAGAAAATAAAGAA

Three Genetic Mutations Substitution Insertion Deletion AATAAGAATGGGAATAGAATGGG… AATAAGAATGGG AATATGAATGGG AATAAGAATGGG AATAAAGAATGGG…

Chromosomal Mutations Chromosomes can be duplicated, portions can be translocated to a different chromosome or inverted on the same, or deleted Usually has profound consequences - sterility or worse Common, e.g. Down’s syndrome 1:700 births Major mode of ‘instantaneous’ speciation in self- fertilizing or inbreeding species, especially plants

Only 1/3 more genes than a worm - Genes like components in assembly lines? Many more harmful mutations per generation Much less coding DNA ( rest junk or spacer or ?? ) Human genomes are complex, but ….

Genetic Load For humans, estimated by reduced fertility and increase in birth defects associated with conceptions between relatives 4 recessive lethals per individual, more than one new lethal per generation In women’s eggs, chromosomal defects in eggs increase with age In men’s sperm, DNA sequence changes increase with age In outbred human conceptions –70% of conceptions never come to term –2 per 1000 live births have genetic defects

What Changes Gene Frequencies? Mutation Genetic drift (random change in small pops) Non-random Mating Migration = Gene Flow Natural Selection

Purifying Selection Dominant or Sex-linked (X or Y) deleterious mutant alleles eliminated rapidly by natural selection Recessive autosomal deleterious mutant alleles reduced slowly by selection –heterozygotes ‘protect’ recessive deleterious mutant alleles –never eliminated: a mutation - selection equilibrium is reached

Stabilizing Selection decreases variation, doesn’t shift mean Trait value Frequency Mean Trait value Frequency Old Mean ParentsOffspring

Directional Selection may reduce variation, shifts mean Trait value Frequency Mean Trait value Frequency Old Mean ParentsOffspring

Disruptive Selection increases variation, may shift mean Trait value Frequency Mean ParentsOffspring Trait value Frequency Old Mean

Sexual Selection

Forms of Sexual Selection Intrasexual (usually male-male competition) –Weapons for within-sex competition Intersexual (usually females choosing males) –Ornaments or signals to attract choosy mates –Why are animals choosy: aesthetic preferences (Darwin’s hyp.) or signals indicate mate quality?

Consequences of Sexual Selection Drives species away from the ecological optimum Major cause of sexual dimorphism via disruptive selection: since ornaments are an advantage in only one sex, there is selection for modifiers that lead to expression in one sex only