LIFESCI 15 Lecture Notes - Lecture 3: Stabilizing Selection, Birth Weight, Disruptive Selection
1/16/18
I. The evolution of the starvation resistance
II. What is evolution
III. What is natural selection?
Restriction of food on aging
- How long can a fly live without food? Can we increase the average time to starvation in a population?
o About 20 hours
o What is you ol let the best flies epodue? top 20% of staatio esistae
▪ Let 5000 flies be born, take out food, wait for 80% to die, put food in, let top 20%
epodue, take out food …
o After 1 generation, the average was about 21 hours
o After 10 generations, the average was about 28 hours
o After 60 generations, the average was 160 hours
- Take home Message #1: Species are not immutable. We can watch the, change in nature or even cause
them to change
- What is evolution?
o A gradual process in which something changes into a different and usually more complex or
better form a e applied to athig e: fashio, as…
o I Eolutioa BIOLOGY…it is a change in allele frequencies within a population
o Gene: section of DNA instructing how to produce a trait
o Allele: one variant of a gene (several may exist)
o We each carry 2 copies of ever gene (one from our mother, one from our father)
o Sometimes the 2 alleles are the same (BB of bb). Sometimes they are different (Bb)
o We a easue the allele feue of B ad
- Take home message #2: evolution is a change in allele frequencies within a population
- Charles Darwin
o Lazy teenager
o Med school drop out
o 1831-36 has Beagle trip around the world
o Pooatie oseatios…
o Years of thinking
o Almost scooped by Alfred Russel Wallace
o Total tiuph: his astat
- Uepeted pattes Dai oseed that got hi thikig…
o Finch variation
▪ Each island had unique species
▪ Island species resembled mainland species
▪ Maybe they used to be the same species
o Similarity between fossils of extinct species and the living species in an area
▪ Extinct glyptodonts looked like G I A N T armadillos
- Some common theme in nature Darwin observed:
o Offspring overproduction
o Competition for scarce resources
o The inheritance of traits; offspring look like their parents
- Darwin concluded that there is a: struggle for existence
o Organisms better suited to an environment have a greater probability of surviving the struggle
and will leave more offspring
o Through evolution, organisms may become better matched with their environment
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