Chapter 23

Question 1

Population

Answer 1

• Groups of individuals inbreeding and producing fertile offspring.
• Populations evolve, individuals don’t

Question 2

Genetic Variation

Answer 2

1. Evolution acts on heritable traits that vary between organisms (genetic variation)
2. Mendel discovered that genes are the basis for heritability
3. Alternative versions of genes (alleles) account for variation in inherited characters:
   - organisms inherit 2 copies of each gene (1 per parent)
   - if alleles differ, dominant determines appearance and recessive has no noticeable effect
   - alleles separate during gamete formation, and end up in different gametes (Law of Segregation)

Question 3

Sources of Genetic Variation

Answer 3

• Sexual reproduction = recombination = novel genotypes (Law of Independent Assortment)
• No change in allele frequencies, but novel combinations can be acted upon by natural selection.

Question 4

Mutations

Answer 4

Variations in Alleles:

• rare
• mostly in somatic cells (not passed on to next generation)
• While variation within a population is essential for evolution to occur, it does not guarantee that a population will evolve.

Question 5

Allele Frequencies

Answer 5

• Every allele has a frequency (proportion) in the population
• Number of alleles = individuals x2 (diploid)
• The frequency of alleles adds up to 1: p = dom and q = rec.
• see review lecture for calculations*

Question 6

Hardy-Weinberg Principle

Answer 6

• Hardy-Weinberg equation calculates the expected frequency of genotypes from allele frequency
• Frequencies of alleles and genotypes in a population remain constant from generation to generation
• H-W may be used to test whether or not evolution is occurring at a specific locus in a population
• Describes a population that is not evolving. If the theory does not hold then the population is not evolving.
• p^2 = 2qp + q^2 = 1
• p^2: frequency of homo dominant
• 2pq: frequency of hetero
• q^2: frequency of homo recessive
• SEE REVIEW LECTURE*

Question 7

Hardy-Wienberg Equilibrium

Answer 7

-When a population is not in H-W equilibrium the observed outcome does not match the expected

Question 8

5 Conditions for Non-Evolving Populations Rarely Met in Nature

Answer 8

1. No mutations
2. Random mating
3. Large population size
4. No gene flow
5. No natural selection

Question 9

3 Evolution Factors

Answer 9

1. Natural Selection
2. Genetic Drift
3. Gene Flow

Question 10

Natural Selection

Answer 10

1. Acts on phenotype
2. Adaptive evolution
3. 3 Forms of Selection:
   - Directional
   - Disruptive
   - Stabilizing

Question 11

Directional Selection

Answer 11

Extreme phenotype favoured

Question 12

Destructive Selection

Answer 12

Phenotypes extremes favoured

Question 13

Stabilizing Selection

Answer 13

Intermediate phenotypes favoured

Question 14

Genetic Drift

Answer 14

1. Chance changes in allele frequencies
   - reduces genetic variation through loss of alleles
   - important in small populations

Question 15

What do small populations result from?

Answer 15

1. The Founder Effect

2. The Bottleneck Effect

Question 16

The Founder Effect

Answer 16

• a few individuals isolated from larger populations

- allele frequencies in founder population different from parent population

Question 17

The Bottleneck Effect

Answer 17

• Sudden reduction in population size

- Resulting gene pool different from parent population

Question 18

Gene Flow

Answer 18

• movement of alleles among populations due to movement of fertile individuals or gametes (e.g. pollen)
• reduces variation among populations over time
• if there is no gene flow they are independent from one another