hbio - lecture #1 // 8/28

biological evolution

a change in the genetic make-up of a population over time

what evolution occurs in

populations not people!!!!

population

a group of organisms potentially capable of successful reproduction

the largest reproductive population

species

the unit of evolution

population

phenotype

how a gene is expressed

gene pool

the sum of all alleles carried by the members of a population

evolution

a change in the genetic make-up of a population over time.

evolution occurs in what and not what

occurs in populations, but individuals do

what evolves and what doesn't evolve?

the genetic make-up as evolution is a change in allele frequency of a population

allele

different version of a gene, ex) one gene that codes for eye colors, but there are alleles for other colors

mutation

alteration in the DNA and the source of variation in the population, very rare and RANDOM

natural selection increases what? and decreases what

increases the frequency of positive mutations, but decreases the frequency of negative mutations. NON-RANDOM

"CCR5-delta 32 gene

"

a random mutant present in European populations but is almost absent from all others. from 1347-1450, about a 1/4th died from the bubonic plague. people with two copies of the gene surivived

examples of natural selection

Parasite destroyed male embryos of Hypolimnas bolina in the Samoan Islands --> Sex imbalance, 1% male in butterfly population --> 10 generations, males returned to 40% of population even with present parasite. THEY PASSED ON THE GENE FOR IMMUNITY (advantangeous traits)

natural selection favorable

favorable traits become more common in a population, and over more time as they become more common, new species are formed.

darwins finches

on the galapagos islands, ~4 habitable islands, differences from other islands were body size and beak size. beak is important since 1) big -> break big seeds, 2) smaller to drink nectar from flowers. demonstrated different environments

population in natural selection

mating pairs generally have >2 offspring, but populatioin size typically stays the same since it can't too be too big otherwise there won't be enough resources.

alfred russel wallace

they were #rivals

variability

you need variation in a population

differential fitness

some members do better (ex. surivive and reproduce) than others

why are offsprings of successful members more successful

they inherited selectively advantageous traits

what happened to less successful

there is a removal of selectively disadvantageous traits

what makes animal life hard

different environments, competition for resources ex) mates, foods.

Modern Definition of Natural Selection

differential contribution of genotypes to the gene pool of subsequent generations (under natural conditions) due to differential reproductive success

Directional Selection

a mode of natural selection in which a phenotype is favored, causing the allele frequency to shift over time in the direction of that phenotype

directional selection example

ex) industrialization in britan, a lot of coal burning so ash everywhere, so the original phenotype of pepper both was white/black, they're all dying rapidly becuase they're so visible against the black sky, but then there's a mutation that makes them black. once the black ash clears up, the white ones come back

stabilizing selection

mode of NS wheregenetic diversity decreaes & population mean stabalizes on paticular trait

stabilizing selection ex)

7 pounds is average birth across diff countries, too overweight mom is hurt, underweight it's premature

Sexual selection

"Differential reproductive success among the members of the same

sex within a given species,

• Struggle between males to gain access to females

• Struggle by a female to choose the right mate"

selection is driven by females

Evolutionary change through selection for certain male phenotypes • Examples: Larger canines, brighter coloration, larger body size

why females fight for males

The sex with the more limited reproductive potential should be competed over by the sex with the greater reproductive potential

Intrasexual selection

competition between members of the same sex (e.g., male-male competition). mothers need to eat2x calories to breastfeed, need babies to surivive and reproduce, which is they can be selective

genetic drift

changes that occur because of sheer chance (RANDOM), Without strong selective pressure, populations will naturally change at random

Founder effect

Component of genetic drift • Can occur when a segment of the original population becomes isolated or cut off or migrates to new areas • The migrating group represents a small sample of original population

Founder effect - amish

amish population in PA - skeletal disorder, didnt decrease because there wasnt enough new variation

"Population bottlenecks

"

"• Component of Genetic drift

• Occurs when a population’s size is reduced for

at least one generation

• Reduction in gene variation means population

may not adapt to new selection pressures"

gene flow

"RANDOM,. New alleles introduced to the

population

▪ May or may not involve physical

migration"

"gene flow - Reproductive isolation

"

no gene flow

adaptation

"a trait that increases fitness

• Built by natural selection

• Being ‘fit’ means being

adapted to your environment… but environments change

• The process never stops"

red queen hypothesis

"Everything is adapting

• An adaptation is a feature that increases fitness"

Predator/Prey coevolution

"Each successive generation adapts to survive better than the previous one

Ex)

• Cheetahs and Gazelles

•The cheetah has evolved to become the fastest predator,

while the gazelle has evolved to become faster and elusive"