1. Genes, Variation & Change in Populations
evolution

2. POINT > Define gene pool, allele, and allele frequency
POINT > Discriminate between single gene and polygenic traits
POINT > Define the Normal Distribution
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits

3. POINT > Define gene pool, allele, and allele frequency
A gene pool is all of the alleles present in a population
Allele frequency is the number of times an allele occurs, divided by the total number in the population
B allele (black) – 40% or 0.4
b allele (brown) – 60% or 0.6

4. WB Check: What is a gene pool?
In a population of mice, suppose there are two alleles for fur length, L (long fur) and l (short fur).
If half the population is homozygous dominant and half is homozygous recessive, what is the allele frequency for the “L” allele?
If an invasive species kills all the long-furred mice, what is the new allele frequency for “l”?

5. WB Check:
In a population of 100 mice, how many total alleles are there for fur length?
If 50% of the above population is homozygous dominant, 25% is homozygous recessive, and 25% is heterozygous, what are the allele frequencies for the L and l alleles?
“L” frequency = “l” frequency = 0.375

6. POINT > Define gene pool, allele, and allele frequency
Evolution occurs when there is change in the frequency of alleles in a population over time
Populations evolve, not individuals!

7. POINT > Discriminate between single gene and polygenic traits
The number of phenotypes for a trait is based on how many genes control that trait
Traits controlled by a single-gene usually have only 2-3 phenotypes (like our Mendelian examples)
Through natural selection, the environment causes changes in allele frequency. This changes phenotypic frequencies
ex. Industrial melanism in moths

8. The peppered moth has these two phenotypes
Industrial melanism in the peppered moth
The peppered moth has these two phenotypes

9. Industrial melanism in the peppered moth
Prior to the industrial revolution, light colored trees favored the light color moths. The frequency for the light color allele was much higher than the dark allele

10. Industrial melanism in the peppered moth
Factory pollution killed lichen and turned tree bark brown and black in industrial areas

11. Industrial melanism in the peppered moth
The blackened trees favored the darker moth phenotype. The frequency for the dark color allele rose in the population, while the frequency of the white allele dropped

12. WB Check:
Which is true about industrial melanism in the peppered moth?
a) Moths with the dark phenotype are healthier
b) Overall allele frequencies remain constant
c) Environment determines which moths are most fit
d) Individual moths evolve from light color to dark

13. POINT > Discriminate between single gene and polygenic traits
The number of different phenotypes for a trait is based on how many genes control that trait
Polygenic traits are controlled by more than one gene
(most traits are in this category)
The environment determines fitness on the entire range causing various results and many phenotypes

14. POINT > Discriminate between single gene and polygenic traits
The number of phenotypes for a trait is based on how many genes control that trait
Polygenic traits = many phenotypes

15. WB Check:
In species X, there is 1 gene that controls trait A and 5 genes that control trait B. Which trait would have fewer phenotypes?
How many different phenotypes would you expect for trait A?

16. POINT > Define the Normal Distribution
Normal Distribution (Bell Curve)

17. 1. Stabilizing selection (ex. human birth weight)
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
1. Stabilizing selection (ex. human birth weight)
Large
Birth Weight
Small
Birth Weight

18. 1. Stabilizing selection (ex. human birth weight)
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
1. Stabilizing selection (ex. human birth weight)
Small
Birth Weight
Large
Birth Weight

19. Stabilizing selection (ex. human birth weight)
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Stabilizing selection (ex. human birth weight)
Large
Birth Weight
Small
Birth Weight

20. Stabilizing selection (ex. human birth weight)
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Stabilizing selection (ex. human birth weight)
Small
Birth Weight
Large
Birth Weight

21. Stabilizing selection (ex. human birth weight)
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Stabilizing selection (ex. human birth weight)
Small
Birth Weight
Large
Birth Weight

22. POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Stabilizing selection: Intermediate phenotypes have higher fitness than others
Small
Birth Weight
Large
Birth Weight

23. Stabilizing selection leads to less variation in population
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Stabilizing selection leads to less variation in population
Small
Birth Weight
Large
Birth Weight

24. WB CHECK:
Which phenotypes are selected for during stabilizing selection?

25. Directional selection (ex. Drug-resistant bacteria)
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Directional selection (ex. Drug-resistant bacteria)
Low Drug
Resistance
High Drug
Resistance

26. Directional selection (ex. Drug-resistant bacteria)
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Directional selection (ex. Drug-resistant bacteria)
Low Drug
Resistance
High Drug
Resistance

27. Directional selection (ex. Drug-resistant bacteria)
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Directional selection (ex. Drug-resistant bacteria)
Low Drug
Resistance
High Drug
Resistance

28. Directional selection (ex. Drug-resistant bacteria)
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Directional selection (ex. Drug-resistant bacteria)
Low Drug
Resistance
High Drug
Resistance

29. Directional selection (ex. Drug-resistant bacteria)
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Directional selection (ex. Drug-resistant bacteria)
Low Drug
Resistance
High Drug
Resistance

30. POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Directional selection (ex. Drug-resistant bacteria): one phenotypic extreme is favored
Low Drug
Resistance
High Drug
Resistance

31. POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Directional selection leads to change within species & potential speciation under certain circumstances (isolation)
Low Drug
Resistance
High Drug
Resistance

32. WB CHECK:
Which phenotypes are selected for during directional selection?

33. Disruptive selection (Lazuli bunting coloration)
Male
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Female
Disruptive selection (Lazuli bunting coloration)
Dull,
Brown Males
Bright,
Blue Males

34. Disruptive selection (Lazuli bunting coloration)
Male
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Female
Disruptive selection (Lazuli bunting coloration)
Dull,
Brown Males
Bright,
Blue Males

35. Disruptive selection (Lazuli bunting coloration)
Male
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Female
Disruptive selection (Lazuli bunting coloration)
Dull,
Brown Males
Bright,
Blue Males

36. Disruptive selection (Lazuli bunting coloration)
Male
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Female
Disruptive selection (Lazuli bunting coloration)
Dull,
Brown Males
Bright,
Blue Males

37. Disruptive selection (Lazuli bunting coloration)
Male
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Female
Disruptive selection (Lazuli bunting coloration)
Dull,
Brown Males
Bright,
Blue Males

38. Disruptive selection (Lazuli bunting coloration)
Male
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Female
Disruptive selection (Lazuli bunting coloration)
Dull,
Brown Males
Bright,
Blue Males

39. POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Disruptive selection: Extreme individuals have higher fitness than others
Dull,
Brown Males
Bright,
Blue Males

40. Disruptive selection: If conditions continue, speciation may occur
POINT > Describe stabilizing, directional, and disruptive selection on polygenic traits
Disruptive selection: If conditions continue, speciation may occur

41. WB CHECK:
Which phenotypes are selected for during disruptive selection?
Which type of selection would not lead to speciation?
Which type of selection reduces variation?

42. Homework: Read pages 482-489 Assess page 486 #1-3 Workbook pages 325-328