Download Evolution on a Small Scale

Chapter 15
(Pg 233-244)
 To
an evolutionary biologist—having more
fertile offspring than other individuals
 Being adapted to a particular environment
increases those chances
 BUT, there’s also sexual selection
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
Not based strictly on environment, but on
displays and rituals
Male and female choice
 Small,
measureable changes in a population
from one generation to the next
 Variation itself cannot bring about evolution
 Those variations must impart some sort of
survival and/or reproductive advantage
 Population
genetics: described in terms of
the gene pool

Characterized by allele frequencies





How common is any given allele in that population
Are 99% of the alleles recessive, or is it a combination
of multiple alleles?
In this case, you just look at the frequency of
individual alleles, not how they are paired
Assumes random mating
Predicts allele frequency in next generation
p = frequency of the dominant allele
q = frequency of the recessive allele
p2 + 2pq + q2 = 1
p2 = DD
2pq = Dd
q2 = dd
No mutations (source of variation)
No gene flow in or out of the population
(migration can increase variation in a
population)
Random mating
1.
2.
3.
1.
2.
No genetic drift (need a large population)
4.
1.
5.
Assortative—mating with similar individuals,
divides population into two subgroups
Sexual selection—attracting a mate
Bottleneck and founder effect
No selection
Umm…yeah. These conditions are hardly ever
met.
So—microevolution happens.
These conditions tell us what drive evolution.
Can measure the deviation from the
equilibrium to measure degree of
evolution.
 Individuals
show differential survival and
reproduction rates based on factors in nature


Predators, competition for food and resources
Non-living factors (temperature, salinity, pH…)
 Directional—when
population is pushed
toward one extreme or another
 Stabilizing—average is selected for, extremes
of the trait narrow in range
 Disruptive—extremes are favored and middle
value decreases in frequency
 Evolution
and natural selection have to
“work with” what is available
 It would be great for birds if they had
lightweight, titanium bones, but bird’s
ancestors had Ca based bones
 Blind spot in vertebrate eyes
 Wisdom teeth that cause us problems
 Human lower back problems
 Sometimes,
the benefit is worth the cost
 Hidden
benefits to “bad” alleles—malaria
and sickle cell trait
 Gene flow into a population
 New mutations
 Changing environments
 New gene combinations due to sexual
reproduction
 Heterozygotes “hide” recessive alleles—
natural selection works on traits, not
individual alleles