1. Evolution Notes
Unit 7

2. Provide a record of species that lived long ago.
Support for Evolution
The fossil record
Provide a record of species that lived long ago.
Show that ancient species share similarities with species that now live.
Darwin traveled on HMS Beagle from England-5 yr journey to coast of S America & Pacific Islands.
Glyptodont
Armadillo

3. Geographic Distribution
Evolution
Support for Evolution
Geographic Distribution
The distribution of plants & animals that Darwin saw first suggested evolution.
He found evidence of species changing over time. Fossils of huge animals-giant armadillo. Similar to living species.
Noticed island plants & animals looked like but not identical to plants and animals on south American continent.
So indv from S. American continent had migrated to islands.
Rabbit
Mara

4. Homologous Structures
Anatomically similar structures inherited from a common ancestor
He compared body parts of diff species. Evidence of homo structures.
Appearance across diff species offers strong evidence for common descent
Forelimbs of vertebrates-similar bones
Homo structures are diff in detail but similar in structure

5. Same function but different structure
Evolution
Analogous Structures
Same function but different structure
NOT inherited from common ancestor.
Structures that perform similar function but not similar in orgin.

6. Vestigial Structures Evolutionary theory
Structures that are the reduced forms of functional structures in other organisms.
Evolutionary theory
predicts that features of ancestors that no longer have a function for that species will become smaller over time until they are lost.
No longer serve a purpose.
Wings in ostrich-used for balance-not for flight. Large bodies and long fast legs is enough to avoid predators.
Genes for coding for larger wings was not preserved.
Took many generations for vest structures to shrink

7. Evidence of Evolution Embryology
Closely related species will have more similarities/ less differences in their
stages of embryological
development.
Distantly related species
will show less similarities/
more differences in their
Evidence of Evolution

8. Evidence of Evolution Molecular evidence: DNA
The more closely related you are, the more similar the DNA
DNARNAPROTEIN!

10. Evolution
Shaping Evolutionary Theory
Natural Selection
Acts to select the individuals that are best adapted for survival and reproduction

11. Evolution
Stabilizing selection operates to eliminate extreme phenotypes when avg phenotype leads to higher fitness.
Ex. Siberian Husky-medium height and build helps them do their job in the snow!
Stabilizing selection favors the norm, the common, average traits in a population. Look at the Siberian Husky, a dog bred for working in the snow. The Siberian Husky is a medium dog, males weighing 16-27kg (35-60lbs). These dogs have strong pectoral and leg muscles, allowing it to move through dense snow. The Siberian Husky is well designed for working in the snow. If the Siberian Husky had heavier muscles, it would sink deeper into the snow, so they would move slower or would sink and get stuck in the snow. Yet if the Siberian Husky had lighter muscles, it would not be strong enough to pull sleds and equipment, so the dog would have little value as a working dog. So stabilizing selection has chosen a norm for the the size of the Siberian Husky.

12. Directional selection makes an organism more fit.
Evolution
Directional selection makes an organism more fit.
Favors the ONE extreme phenotype
Ex. Greyhound Dog-bred for extreme speed!
Directional selection favors those individuals who have extreme variations in traits within a population.
EX: breeding of greyhound dog. Early breeders interested in dog with the greatest speed. Carefully selected from a group of hounds who ran the fastest. From their offspring, the greyhound breeders again selected dogs who ran the fastest. By continuing this selection for those dogs who ran faster than most of the hound dog population, they gradually produced a dog who could run up to 64km/h (40mph).
One single phenotype is favored causing the genetic variance to shift

13. Example: In an environment with BOTH black and white rocks….
Evolution
Disruptive selection - process that splits a population into two groups.
Example: In an environment with BOTH black and white rocks….
White and Black rabbit lives, but grey rabbit dies
Natural Selection can select for two or more phenotypes-both have advantages
Population of rabbits were put into an area that had very dark black rocks and white colored stone, the rabbits with black fur would be able to hide from predators amongst the black rocks and the white furred rabbits would be able to hide in the white rocks, but the gray furred rabbits would stand out in both of the habitats and thus would not survive.

17. Evolution
Mechanisms of Evolution
Population genetics
Hardy-Weinberg principle states that when allelic frequencies remain constant, a population is in genetic equilibrium.

18. Evolution

20. Genetic Drift
A change in the allelic frequencies in a population due to chance & random mating
As an analogy, imagine a population of organisms represented as 20 marbles in a jar, half of them red and half blue. These two colors correspond to two different gene alleles in the population. The organisms that are reproduced in a generation are represented in another jar. Each new generation the organisms will reproduce at random. To represent this reproduction, randomly pick a marble from the original jar and deposit a new marble with the same color as its "parent" in the second jar. Repeat the process until there are 20 new marbles in the second jar. The second jar will then contain a second generation of "offspring", 20 marbles of various colors. Unless the second jar contains exactly 10 red and 10 blue marbles there will have been a purely random shift in the allele frequencies.
Repeat this process a number of times, randomly reproducing each generation of marbles to form the next. The numbers of red and blue marbles picked each generation will fluctuate: sometimes more red, sometimes more blue. That is genetic drift – random variations in which organisms manage to reproduce, leading to changes over time in the allele frequencies of a population.
In smaller populations -effects of genetic drift are more pronounced - chance of losing an allele increases

21. Often caused by a natural disaster
Evolution
Bottleneck
a significant % of a population or species is killed or otherwise prevented from reproducing and can rebound later
Often caused by a natural disaster

22. Founder Effect
Loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population
Mainland
Island 3
Island 2
Island 1

23. Nonrandom Mating
Promotes inbreeding & could lead to a change in allelic proportions favoring indv that are homozygous for particular traits

24. What is a gene pool?
Gene pool – combined genetic info of all members of a population
Contains two or more alleles (genes) for the same trait

25. Allele frequency - a measure of how common a certain allele is in the population
G = Green
g = brown

26. Gene Flow Genes entering or leaving a population AKA. Migration
Emigration Genes LEAVING a population
Immigration INCOMING genes in a population

27. Evolution
Coevolution
Relationship between two species might be so close that the evolution of one species affects the evolution of the other species.
Mutualism

28. Evolution
Convergent Evolution
Unrelated species evolve similar traits even though they live in different parts of the world.

29. Behavioral isolation- patterns of courtship may be different.
Prezygotic isolation prevents reproduction by making fertilization unlikely.
Western & Eastern meadowlarks use different songs for attracting a mate…won’t mate with each other
Eastern meadowlark and Western meadowlark
Behavioral isolation- patterns of courtship may be different.

30. Prezygotic isolation
Temporal isolation- different groups may not be reproductively mature at the same season, month, or year.

31. Prezygotic isolation
Ecological isolation- not in the same habitat where they are likely to meet.

32. Prevents offspring survival or reproduction
Postzygotic isolation occurs when fertilization
has occurred but
a hybrid offspring
cannot develop
or reproduce.
Prevents offspring survival or reproduction
Liger

33. Evolution
Adaptive Radiation
Can occur in a relatively short time when one species gives rise to many different species in
response to the
creation of new
habitat or some
other ecological
opportunity