1. Unit 16 Notes: Page 49 Test Date: 5/24/18
Put a pocket on page 49
Unit 16 Notes: Page 49 Test Date: 5/24/18
Evolution as Genetic Change

2. A. Natural Selection Never acts directly on genes
Can only affect which individuals will
Survive and reproduce OR Die without reproducing

3. 1. If an individual dies without reproducing
Its alleles are not contributed to the population’s gene pool
Gene pool consists of ALL of the alleles in ALL of the individuals in a population.

4. 2. If an individual produces many offspring
Its alleles:
Stay in the gene pool
Can increase in frequency

5. B. Natural Selection on single gene traits (traits controlled by one gene)
Can lead to changes in allele frequencies.
Uncomplicated because only 2-3 phenotypes
Can lead to evolution

6. C. Natural Selection on Polygenic Traits
More complex
Polygenic traits produce a range of phenotypes
Can usually fit a bell curve
Can affect the distribution of phenotypes three ways:
Directional selection
Stabilizing selection
Disruptive selection

7. Phenotype on one side increases and phenotype 1.
Pushes the bell curve in one direction.
Phenotype on one side increases and phenotype
on the other end is lost.

8. Directional Selection (don’t write green)
One extreme form of the trait has highest fitness.
Over a long period of time directional selection results in:
1. Shift (toward one extreme end)
2. There is a new trait that occurs more frequently
sselllllllllllll

9. Phenotypes in the center and loses phenotypes on each extreme.2.
Increases the
Phenotypes in the center and loses phenotypes on each extreme.

10. Stabilizing Selection (don’t write green)k
sselllllllll
average form of the trait has higher fitness than does either extreme.
Stabilizing selection results in:
loss of the extreme forms
decrease in genetic variation.
3. All individuals will have the alleles for the highest fitness

11. Disrupts the bell curve and splits it down the center.3.
Disrupts the bell curve and splits it down the center.
Phenotypes on each end increase and
phenotype in the middle Decrease.

12. Disruptive Selection (don’t write green)k
llssellllllllllll
Extreme forms of the trait have higher fitness than the average.
Disruptive selection results in:
Increase in both extremes.
2. Loss of intermediate forms.

13. D. Genetic Drift – a change in gene pool due to chance
Individuals that carry a particular allele may reproduce more offspring than others by chance NOT by natural selection.
Over time a series of these occurrences can cause an allele to increase in frequency within the population.
More likely to occur in a small population because laws of probability are less accurate in small populations

14. E. Founder Effect
If a small group is separated by chance from a population, the allele frequency of the new, smaller population is very likely to be significantly different from the original population it came from.

15. Founder Effect in an insect population

16. F. Evolution vs. Genetic Equilibrium
Genetic Equilibrium- situation in which allele frequencies remain constant.
Understanding what happens when there is no change helps scientists understand how evolution works.

17. G. Hardy-Weinberg Principle
States that allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change.

18. Five Conditions are required to maintain genetic Equilibrium
Random mating
Large population
No immigration or emmigration
No mutations
No natural selection