Evolution: 2.2

George Mendel

• Revealed the laws of genetic inheritance (segregation and independent assortment)

• Showing the laws for how traits and variations are independently inherited, ensuring there is always a permanent supply of natural variation for Darwin’s natural selection to act upon.

• Explained how traits were actually passed down, so helpful ones could pass through generations!

Blended vs Particulate

-Blended: what Darwin thought. That offspring tend to resemble their parents—and where parents differ in phenotype, offspring exhibit an intermediate value. Here, the process of inheritance reduces variation in the population (so not good for his theory).

• Particulate: what Mendel thought. That genes don’t blend but instead are solid. What differs is gene expression

DNA

a double-stranded molecule composed of two strands of nucleotides that wind around one another, held together with hydrogen bonds to form a double helix

Gene

Def: portion of genome that, when transcribed, forms a product

Transcription

When RNA polymerase binds to a promoter, double-stranded DNA is unwound, allowing the polymerase to access that segment of DNA and to synthesize a complementary RNA molecule. The polymerase shown here is moving to the right

After transcription?

Intron splicing, then translation then protein.

Dominance vs co/ incomplete dominance

• RR and Rr same phenotype

• Rr is mix of RR and rr.

realistic?

Mutations

Mutations can have different effects on a sequence depending on WHERE they happen.

• Make new variations randomly. Usually leads to no significant effect (coding for the same protein).

• Synonymous, nonsynonymous, and nonsense describe how the protein changes (the effect on the amino acid sequence).

• Inframe and frameshift describe how the DNA letters shift (the effect on the reading frame).

Chromosomes

Recombination shuffles existing variation, and only happens during meiosis. Not mitosis.

Mutations rates vary across species

1. Among microbes, the per-site mutation rate decreases with genome size.

WHY: Smaller genome, have massive population. Natural selection.

2. Cellular organisms, the per-site mutation rate increases with genome size.

WHY: Larger genome, smaller population in comparison. Proof reading for the larger genome. Also has junk DNA unlike microbes.

Mutations and environment

Mutations have different effect on fitness depending on WHERE in the genome they happen, and the environmental conditions.

• Distribution of fitness effects for single gene mutations

• Ex: heat shock proteins reg. heat. If mutated, yeast cant survive higher temp.

• Ex: sickle cell anemia. Bad in high elevations, not as bad in African populations with high malaria rates.