1. The Evolution of Populations

2. Review of Genetic Terminology
In Genetic Crosses of two organisms:
“P” refers to the parental generation.
“F1” are the offspring of the parents or the first generation.
“F2” are the offspring of the “F1” or the second generation.

3. Genetic Terminology continued…
Alternative forms of genes cause variations in inherited characteristics in offspring.
The alternative forms are called alleles.
Offspring get two alleles for each trait, one from each parent.

4. Genetic Terminology Continued…
If two alleles are different, the dominant allele will be fully expressed meaning that is the trait that is seen in the offspring.
The recessive allele is not seen in the offspring if the dominant allele is present.

5. More Genetic terminology…
Homozygous means organisms have two of the same alleles for a particular trait.
Example: If the dominant allele is
“T” for tall and “t” for short, then “TT”
is homozygous dominant and “tt” is
homozygous recessive.

6. Genetic terminology continued…
Heterozygous means organisms have two different alleles for a trait.
Example: using previous alleles
“Tt”
This organism would express the dominant trait. It is heterozygous dominant.

8. Finally…for genetic terminology
Phenotype is the physical expression of an organism’s traits, or what does it look like (appearance, chemistry, behavior, etc.).
Evolution can only work on phenotype.
Genotype is an organisms genetic makeup.

10. Mutation and Sexual Reproduction produce genetic variation that makes evolution possible

11. Microelvolution is evolution on the smallest scale.
Change in allelic frequencies of a population over generations.
Mutations are the only source of new genes and new alleles.

12. Mutations and Genetic Variation
Only mutations in gametes can be passed to offspring.
Point mutations are changes in one DNA base in a gene.
Chromosomal mutations delete, disrupt, duplicate, or rearrange parts of chromosomes and are almost always harmful.

13. Sexual Recombination most important source of genetic variation.
Recombination of new alleles that already exist in a population.
Due to:
Crossing over during meiosis.
Independent Assortment during meiosis.
Fertilization

14. Mutations

15. Sources of Genetic Variation

16. Population Genetics
Study of how populations change genetically over time.
Remember: Population is a group of the same species that live in the same area, interbreed, and produce fertile offspring.

17. Gene Pool All of the alleles present for all genes in the population.
In a diploid organism, each individual has two alleles for each gene (trait), and may be either homozygous or heterozygous.
If all members are homozygous for the same allele, the allele is said to be fixed;
there will be no change.
The greater the number of fixed alleles, the lower the species diversity.

18. Factors That Can Alter Allelic Frequencies
Mutations can alter gene frequency, but they are rare.
Major Factors that alter allelic frequency are:
Natural Selection
Genetic Drift
Gene Flow

19. Natural Selection Affects Allelic Frequencies.
Results in alleles being passed to the next generation in proportions different from the frequencies in the parents generation.
Individuals with variations better suited to the environment tend to produce more offspring than those with variations that are less suited.

20. Genetic Drift Affects Allelic Frequency
The unpredictable flucuation in allelic frequency from one generation to the next.
Affects smaller populations more.
Random, non-adaptive change in allelic frequency.
Examples of Genetic Drift:
Founder Effect
Bottleneck Effect

21. Founder Effect
A few individuals become isolated from a larger population.
Establish a new population whose gene pool is not the same as the original population.

23. Bottleneck Effect
Sudden change in the environment (for example, an earthquake, flood, or fire) drastically reduces the size of the population.
The few survivors that pass through the restrictive “bottleneck” may have a different gene pool than the original population.

25. Gene Flow
Occurs when a population gains or loses alleles by additions or subtractions from the population.
Immigration and Emmigration
Tends to reduce differences between populations

27. Hardy-Weinberg Theorem
Describes a population that is not evolving.
States that the frequencies of alleles and genes will remain the same over generations, unless acted on by forces other than segregation and recombination.
Population is at Hardy-Weinberg Equilibrium.

28. Five Conditions for Hardy-Weinberg Equilibrium
No Mutations
Random Mating
No Natural Selection
The population must be extremely large. (No Genetic Drift)
No Gene Flow

29. Hardy-Weinberg Equation
p + q = 1

31. Natural Selection only mechanism that consistantly causes adaptive evolution.
Relative Fitness is the contribution an organism makes the gene pool of the next generation relative to the contribution of other members.
Measured by reproductive success.
Natural Selection works on phenotype directly and genotype indirectly

32. Frequency Distribution of Heritable Traits can be altered in three ways.
Directional Selection
Disruptive Selection
Stabilizing Selection

33. Directional Selection
Individuals with one extreme of a phenotypic range are favored, shifting the curve toward that extreme.
Example: Large black bears survived extreme cold better than smaller ones.

34. Disruptive Selection
Favors individuals on both extremes of a phenotypic range rather than individuals with intermediate phenotypes.
Example: A population has individuals with either large beaks or small beaks, but few with intermediate sizes.

35. Stabilizing Selection
Acts against both extreme phenotypes and favors intermediate varieties.
Birth weights of most humans lie in a narrow range, as those babies who are very large or very small have higher mortality.

37. How is genetic variation preserved in a population?
Diploidy: Recessive trait may be hidden from selection.
Heterozygous Advantage: Individuals who are heterozygous sometimes have a selective advantage for survival.

38. Heterozygous Advantage

39. Why doesn’t natural selection produce perfect organisms?
Selection can only act on existing variations.
Evolution is limited by historical constraints.
Adaptations are often compromises.
Chance, natural selection and the environment interact.