1. Evolution Darwin’s Ideas Hardy-Weinberg Evidence for Evolution Speciation and Mechanisms Origins

2. How do genetic variations occur?
What is Evolution?
Change in the genetic makeup of a population over time.
Fitness – those with favorable variations for survival and reproduction.
Populations can evolve, not individuals.
Diverse gene pool good for long-term survival of a species. Genetic variations are important!
How do genetic variations occur?

3. Where does Variation come from?
Mutation
random changes to DNA
errors in mitosis & meiosis
environmental damage
Sexual reproduction
mixing of alleles
genetic recombination
new arrangements of alleles in every offspring
new combinations = new phenotypes

4. Genetic variation in a population

5. Essence of Darwin’s ideas
Natural selection
heritable variation exists in populations
over-production of offspring
more offspring than the environment can support
competition
for food, mates, nesting sites, escape predators
differential survival
successful traits = adaptations
differential reproduction
adaptations become more common in population

6. Lamarckian vs. Darwinian view
in reaching higher vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring
Darwin
giraffes born with longer necks survive better & leave more offspring who inherit their long necks 

7. Natural Selection Major mechanism of evolution
Environment is always changing
Acts upon the phenotype of the population
Based on Darwin’s idea that resources are limited and that there is competition for those resources.
Adaptation = a genetic variation favored by natural selection.
When allele frequencies shift, speciation occurs
Thus, the frequency change is NOT RANDOM

8. DIRECTIONAL SELECTION STABILIZING SELECTION
Effects of Selection
Changes in the average trait of a population
DIRECTIONAL SELECTION
STABILIZING SELECTION
DISRUPTIVE SELECTION
giraffe neck
horse size
human birth weight
rock pocket mice

10. Natural selection in action
Insecticide & drug resistance
insecticide didn’t kill all individuals
resistant survivors reproduce
resistance is inherited
insecticide becomes less & less effective
Resistance…
NOT immunity!
MRSA

11. Heterozygote Advantage
Keeps the recessive allele in the population
Ex: Sickle Cell Anemia
aa – dies of sickle cell anemia
Aa – some side affects BUT resistant to malaria!
AA – no disease present BUT prone to malaria

12. Hidden variations can be exposed through selection!
Terminal
bud
Lateral
buds
Brussels sprouts
Cabbage
Flower cluster
Leaves
Cauliflower
Flower
and
stems
Broccoli
Wild mustard
Kohlrabi
Stem
Kale
Artificial selection

13. In addition to natural selection, evolutionary change is also driven by random processes…

14. Genetic Drift
Chance events changing frequency of traits in a population
not adaptation to environmental conditions
not selection
founder effect
small group splinters off & starts a new colony
it’s random who joins the group
bottleneck
a disaster reduces population to small number & then population recovers & expands again but from a limited gene pool
who survives disaster may be random
Founders: When a new population is started by only a small group of individuals. Just by chance some rare alleles may be at high frequency; others may be missing; skew the gene pool of new population. Ex: human populations that started from small group of colonists
example: colonization of New World
Bottleneck: When large population is drastically reduced by a disaster-famine, natural disaster, loss of habitat…loss of variation by chance event
alleles lost from gene pool not due to fitness, narrows the gene pool

15. Ex: Cheetahs All cheetahs share a small number of alleles
less than 1% diversity
2 bottlenecks
10,000 years ago
Ice Age
last 100 years
poaching & loss of habitat

16. Peregrine Falcon
Conservation issues
Bottlenecking is an important concept in conservation biology of endangered species
loss of alleles from gene pool
reduces variation
reduces adaptability
Breeding programs must consciously outcross
Golden Lion Tamarin

17. Human Impact on variation
How do we affect variation in other populations?
Artificial selection/Inbreeding
Animal breeds
Loss of genetic diversity
Insecticide usage
Overuse of antibiotics
resistant bacterial strains