1. How Organisms Evolve

2. homework
Read chapter 15
Do the key terms for chapter 15

3. Preface Natural selection is a mindless, mechanical process
some individuals reproduce more successfully than others and that is it
therefore, their traits are more prevalent in the next generation
Darwin understood this but he had NO knowledge of the mechanics of heredity
today, we do

4. How Are Populations, Genes, and Evolution Related?
Understand that the changes observed as an individual grows and develops are not evolutionary changes
Evolutionary changes are those that occur from generation to generation; the changes that cause descendants to be different from their ancestors
Furthermore, these changes cannot be detected by looking at individuals

5. You must look at many individuals across many generations
Evolution is, clearly then, a property of populations
But, populations are comprised of individuals
And, it is the actions and fates of them that determine what traits will get passed on

6. Therefore, inheritance provides the link between the lives of individuals and the evolution of populations

7. A Quick Review of the Principles of Genetics (unit 2 starting on page 141)
1. Genes, influenced by the environment, determine the traits of each individual
there are usually more than one allele(nucleotide sequence) for any given trait. Different alleles generate slightly different forms of the same enzyme which leads to slightly different phenotypes such as, blue eyes, green eyes, and brown eyes

8. 2. The gene pool is the sum of all the genes in a population
In other words, the gene pool consists of ALL the alleles of ALL the genes in ALL the individuals of that population

9. Example
In a population of 100 pea plants(sorry), the gene for flower color would have 200 alleles (peas are diploid so there are 2 color alleles per plant)
All those alleles can produce only 2 phenotypes: purple or white
Analysis of the population shows that some individuals have alleles for white flowers some for purple and some have both

10. continued
If we add up the color alleles of all the plants in the population, we could determine the relative proportions of the different alleles. This is called the allele frequency.
So, if the gene pool for flower color consists of 140 alleles for purple and 60 for white the allele frequencies would be…
correct! 0.7 or 70% for purple and 0.3 or 30% for white

11. 3. Evolution is a change of gene frequencies within a population
many people define evolution as a change in outward appearances or behaviors of members of a population
But changes in phenotypes are outward expressions of changes in the gene pool
So, evolution is nothing more or less than a change in the genetic makeup of populations over generations.

12. homework
Do applying concepts chapter 15

13. Hardy-Weinberg Equations

14. The Hardy-Weinberg Principle
States that both allele and genotype frequencies in a population remain constant
that is to say, they are in equilibrium from generation to generation unless disturbing influences are introduced

15. Outside of the lab...
…these disturbing influences are always in effect
Therefore, Hardy-Weinberg equilibrium is impossible in nature

16. In the simplest case... …of a single locus with two alleles
the dominant allele is denoted by T and recessive by t (we’ll use “t’s” because of taste)
Their frequencies are denoted by p an q
frequency (T) = p and frequency (t) = q
p + q =1

17. If the population is in equilibrium...
then we will have frequency (TT) = p2 for the TT homozygotes in the populations
frequency (tt) = q2 for the tt homozygotes
frequency(Tt) = 2pq for the heterozygotes

18. Let’s Look At It This Way
Alleles for any given individual are chosen randomly and independent of each other
Consider two alleles A and a, with frequencies p and q respectively
The different ways to form new genotypes can be derived using Punnet Squares

19. so the formula is p2 + 2pq +q2 = 1

20. The Equilibrium Population
Lets look at it from a different angle
What if there was a population that did not evolve?
What would the characteristics of this population have to be?
The equilibrium population is a hypothetical population that models this

21. The Characteristics of This Hypothetical Population
1. There must be NO mutation
2. There must be NO gene flow between populations (that is, there must be no net migration of alleles into the population or out of the population)
3. The population must be very large
4. ALL mating must be random, with NO tendency for certain genotypes to mate with specific other genotypes

22. 5. There must be NO natural selection; that is, ALL genotypes must be equally adaptive and reproduce equally
Under these conditions, allele frequencies within a population will remain the same indefinitely
If one or more of these conditions are violated, allele frequencies will change and EVOLUTION WILL OCCUR.

23. What Causes Evolution?
Based on the Hardy-Weinburg equilibrium, we can state that evolution occurs due to five major causes
mutation
gene flow
small population size
non-random mating
natural selection

24. STOP!!!
Take chapter 15 quiz 1

25. Mutations Are the Ultimate Source of Genetic Variability
Mutations are inevitable
Cells have a pretty efficient system for protecting the integrity of their genes
Some changes in the nucleotide sequence slip past the check and repair systems
When these changes occur in the cells that produce gametes, the changes can enter the gene pool and be passed on to the next generation

26. Unfortunately, we don’t get superpowers from this.
I don’t have this issue.

27. I do have this one though.

28. Mutations are rare
They occur once in every 100,000-1,000,000 genes per individual in each generation
Therefore mutation alone is not a big factor in evolution, but...
...mutations are the source of new alleles, new heritable variations on which other evolutionary factors can act
as such, they are the foundation of evolutionary change

29. Without mutations, there would be no evolution and no diversity among life-forms.
MUTANTS
RULE!!!

30. Mutations Are NOT Goal-directed
They do not arise as a result of or in anticipation of environmental necessities
They simply happen
This may result in some change in structure and/or function of the organism
Whether they are helpful, harmful or neutral depends on the environment over which the organism has little control
The mutation provides potential

31. Other forces..
Such as migration and natural selection that act on the potential may favor the spread of the mutation through the population or eliminate it.

32. Gene Flow Between Populations Changes Allele Frequencies
Gene flow: When individuals move from one population to another, and interbreed at the new location, alleles are transferred from one gene pool to another.
This alters the distributions of alleles among populations

33. Example: Baboons Baboons live in social groups called troops
Within each troop the females mate with a handful of dominant males
Young males usually leave the troop and join another troop and perhaps become dominant
With this, the males carry genes from one troop to another (gene flow)

34. By the way, baboons are big and strong and scary.

35. See what I mean?
Where is your lip? What is going on here?!
What the hell is this?

36. Gene Flow Can Have Very Significant Effects
Gene flow spreads advantageous alleles throughout the species
Gene flow helps maintain all the organisms over a large area as one species

37. Genetic Drift
Random events eliminate disproportionate numbers of individuals
This can change the allele frequency in the population

38. Random Mating Most organisms DO NOT do this
Only certain members of the population will mate
Therefore the next generation will only be offspring of this select group, whose allele frequencies may differ from the population as a whole
Watch this or this

39. Population bottleneck
A form of genetic drift in which a population becomes extremely small
This leads to differences in allelic frequencies and a loss of genetic variability

40. The Founder Effect
A type of genetic drift in which an isolated population founded by a small group of individuals may develop allele frequencies that differ from the parent population as a result of chance inclusion of disproportionate numbers of certain alleles in the founders

41. Neanderthal Skull: Check out that nose....FOUNDER EFFECT!!!!!!!

42. Survival and Reproduction Influenced by Phenotype
Phenotype depends, at least, partly on genotype
Natural selection tends to favor the reproduction of certain alleles at the expense of others

43. Extinction

44. Natural Selection Can Cause This Too
It is estimated that 99% of all the species that ever existed are extinct
Extinction is almost always caused by environmental change
the 3 major enviromental causes of extinction are
competition among species
introduction of new predators or parasites
habitat destruction

45. STOP!!!
Take chapter 15 quiz 2
then take chapter 15 test