Cycle 6 - Genetic 2, Hardy

Question 1

Define allele, locus, and gene pool

Answer 1

Allele: an allele is a variant form of a given gene

Locus: particular location of a gene on a chromosome

Gene pool: the stock of different genes in an interbreeding population.

Question 2

Explain quantitative, qualitative variation, phenotypic variation

Answer 2

Phenotypic Variation

• Differences in appearance of functions between individual organisms
• Can be caused by genetic differences, environmental factors, or an interaction of the two

Quantitative Variation

• Variation that is measured on a continuum (ex., height in humans) (polygenic traits)

Qualitative Variation

• Variation that exists in two or more discrete states (ex., snow geese are either blue or white) (pleiotropic traits)

Question 3

State the conditions required for hardy-weinberg equilibrium (i.e. 0 evolution; allele frequencies do not change)

Answer 3

1. The population is closed
2. The population is very large
3. No mutation is occurring
4. All genotypes in the population survive and reproduce equally well (no selection)
5. Individuals in the population mate randomly

Question 4

State the hardy-weinberg equations

Answer 4

• p2 + 2pq + q2 = 1
• p + q = 1

p² = frequency of genotype

p = allele frequency

Question 5

Predict what the following will happen to these dihybrid scenerios

1. With no selection
2. Recessive favoured (selective)
3. Dominant favoured (selective)
4. Heterozygote favoured (stabilizing)
5. Homozygotes favoured (disruptive)

Answer 5

1. With no selection
   
   • Allele frequencies will not change, as each are equally fit (hardy-weinburg)
2. Recessive favoured (selective)
   
   • Dominant allele will tend to 0 and eventually disappear
3. Dominant favoured (selective)
   
   • Recessive allele decreases but never fully disappears as it can be masked in fit heterozygous individuals and continually passed on
4. Heterozygote favoured (stabilizing)
   
   • Dominant and recessive alleles stabilize into 0.5 and 0.5
   • This is still selection despite stabilization
   • This population is evolving at first, but not after the stabilization
5. Homozygotes favoured (disruptive)
   
   • The highest initial frequency trends to 1 and the lowest initial frequency tends to 0

Question 6

Explain how gene flow causes evolution

Answer 6

Gene Flow: Organisms or their gametes (e.g., the pollen of flowers) sometimes move from one population to another and may introduce novel alleles into a population

Question 7

Explain how genetic drift causes evolution

Answer 7

Genetic Drift: Sometimes allele frequencies in a population change from one generation to the next simply by chance.

2 unique types:

1. Founder Effect: occurs when a few individuals colonize a distant area and start a new population (seen in inbreeding villages)
   
   • They carry only a small sample of the parent population’s genetic variation. By chance, some alleles may be totally missing from the new population, whereas other alleles that were rare in the original population might be common
2. Bottleneck: factors such as disease, starvation, and hunting may kill a large proportion of the individuals in a population, resulting in a population bottleneck. The large reduction is associated with a decrease in the size of the gene pool that can never be regained.

Question 8

Explain how mutation and natural selection cause evolution

Answer 8

Mutations: Random double-stranded changes in DNA. These cause the most genetic variation.

Natural Selection: stabilizing, directional, disruptive; a change in allele frequencies over time (predictable)

• Only mode that can make a population better suited to its environment

Question 9

Explain absolute and relative fitness

Answer 9

Absolute fitness

• Absolute fitness, W, for a genotype is a measurable quantity that is a representation for reproductive success (ex., number of surviving offspring)
  
  • Ex., W_AA = 20 eggs, W_Aa = 15 eggs, W_aa = 12 eggs
• Relative fitness, w, between 0 and 1: the genotype’s W, absolute fitness value, divided by the W of the most successful genotype
  
  • Ex., w_Aa = W_Aa / W_AA = 0.75
  • 1 = 1 most successful genotype
  • If wAA = wAa = waa, no selection is occurring

Question 10

Explain the pattern of inheritence in assortative populations

Answer 10

If a population begins mating assortative for a certain trait (ex., geese colour), and all genotypes have the same fitnessEx., 250 AA, 500 Aa, 250 aa (hardy-weinberg)

• 250 AA –> 250 AA
• 250 aa –> 250 aa
• 500 Aa –> (does not breed true) –> 250 Aa, 125 AA, 125 aa (1/2 chance of AA, 1/4 chance of Aa or aa)

Question 11

Define:

1. Assortative mating
2. Disassortative mating
3. Inbreeding
4. Inbreeding avoidance

Answer 11

Random mating…

At one trait (ex., white vs. blue geese)

1. Like with like = assortative mating (blue geese like blue geese)
2. Opposites attract = disassortative mating (white throated sparrows with tan striped sparrows)

Genome wide?

1. Like with like = inbreeding (close relatives; similar at several/all traits)
   
   • Leads to fewer heterozygotes and more individuals with recessive genotypes
   • Does not increase frequency, more people just have the recessive
2. Opposites attract = inbreeding avoidance (anything but shared traits)

Question 12

Explain distruptive, directional, and stabilizing selection

Answer 12