1. Genetic drift & Natural Selection
Mechanisms of Evolution
Genetic drift & Natural Selection

2. Five Factors Drive Evolution
Mutation

3. Venom-like proteins first appeared about 200 million years ago

4. Venoms evolved from other proteins

5. Venoms were recruited from other functions

6. I. Natural Selection Green mamba is arboreal
Its venom is most effective against birds.
Black mamba is terrestrial
Its venom is most effective against mammals.

7. OVERPRODUCTION

8. HERITABLE VARIABILITY

9. COMPETITION

10. DIFFERENTIAL REPRODUCTION

11. II. GENETIC DRIFT
The smaller the population, the less genetic variety it has.
In a very small population, alleles can be lost from one generation to the next, simply by random chance.
When a population evolves only because of this type of random sampling error, GENETIC DRIFT is taking place.

12. FOUNDER EFFECT

13. BOTTLENECK EFFECT

14. AND IN 4.5 BILLION YEARS…
The diversity of life on earth around us evolved.

15. Measuring Genetic Change
The study of Population Genetics is the study of how the genetic makeup of populations changes from one generation to the next.
Population geneticists study how genes/traits
maintained
lost
…from a population’s gene pool.
gene pool = all the genes at all the loci in all members of the population

16. Let’s imagine A population of fruit flies with a gene we’ll call “X”
X codes for an important enzyme the fly needs for survival.

17. Let’s imagine
A mutation of the gene results in a mutant allele we’ll call x
X is dominant. x is recessive.
The recessive version of the gene
codes for a “broken” enzyme
that does not work.

18. Mate a heterozygous male with a homozygous XX female

19. Predict offspring ratios with a Punnett Square

20. What if two heterozygotes mated?X

22. Inbreeding
Mating between close relatives increases the chance that recessive alleles will be expressed (in homozygous individuals)

23. Outbreeding
Mating between distantly related individuals decreases the chance that recessive alleles will be expressed.
Outbreeding increases heterozygosity at many gene loci.
This results in….
HYBRID VIGOR

24. Hardy-Weinberg Equilibrium
If there are two alleles for a particular gene
Then
dominant alleles + recessive alleles = 100%
100% can also also be represented as 1.0
The proportion of each allele is also called its FREQUENCY
% = proportion = frequency

25. Hardy-Weinberg Equilibrium
With two alleles, there are three possible genotypes: XX Xx xx

26. Hardy-Weinberg Equlibrium
If a population is not evolving, then you should have the same number of XX , Xx, and xx individuals in every generation. But if the proportions of XX, Xx, and xx change from one generation to the next, then the population is EVOLVING.

27. Hardy-Weinberg Equlibrium
Let’s call the frequency of the dominant allele (X)… p.
Let’s call the frequency of the recessive allele (x)… q.
If only X and x alleles exist, then p + q = 1.0
If you know q, you can figure out p.
But how do we figure out q?

28. Hardy-Weinberg Equilibrium
Every xx individual carries two recessive alleles.
The frequency of the q allele in these homozygotes is represented as q2
Only homozygous recessives will show the recessive trait.
To calculate q, take the square root of q2

29. Hardy-Weinberg Equilibrium
Since p + q = 1.0, then 1.0 – q = p
Once you know both p and q, plug in to the Hardy-Weinberg equation:
p2 + 2pq + q2
p2 is the proportion (frequency ) of XX homozygotes
2pq is the proportion (frequency) of Xx heterozygotes
q2 is the proportion (frequency) of xx homozygotes

30. Hardy-Weinberg Equilibrium
If the relative frequencies of X and x change from one generation to the next, then the population is evolving.
If the proportion of XX, Xx and xx individuals in a population changes from one generation to the next, then the population is evolving.

31. Hardy-Weinberg Equilibrium
A population that is NOT EVOLVING is said to be in Hardy-Weinberg equilibrium.
We can use HW calculations to measure microevolution in populations.