MCMASTER BIO 1M03 EXAM 2025
QUESTIONS AND ANSWERS
Why might Pasteur's experiment be inconclusive? - ANS The swan-necked flask broth may
not support cell growth, or the broth was poisoned. Experiment did not confirm hypothesis that
all cells come from pre-existing cells
Why are replicates important in experiments? - ANS To ensure that results were not
achieved by random chance
What is the definition of a replicate? - ANS Unit that shares a common thing (4 mice in one
cage = 1 replicate)
What does the law of succession suggest? - ANS As one species disappears, a similar one
appears. Suggests ancestors and descendants
What is the difference between vestigial traits and transitional features? - ANS vestigial -
useless features similar to useful features in related species (eg, coccyx in humans, tail in
monkeys)
transitional - intermediate feature seen in fossil species, between ancestral and descended
species (eg, aquatic animal fins, tetrapod limbs)
List potential outcomes of the bottleneck effect - ANS - Potential high frequency of
deleterious alleles that were previously at low frequency in source population
- Different allele frequencies from source population, could lead to speciation
1 @COPYRIGHT THEBRIGHT 2025/2026
,- Strong genetic drift due to small population size
Explain how the tuberculosis bacteria underwent natural selection during and after drug
therapy - ANS Variation: different strains → some resistant to drugs, some died
Heritability: drug-resistant bacteria passed drug-resistant gene to daughter cells
Differential fitness: bacteria that survived produced offspring
Selection: drug-resistant allele had higher chance of survival through drug therapy
Give three types of homologies. Provide an example for each - ANS Genetic: similarity in
RNA, DNA, amino acids (eg, AUG start codon shared with many living organisms)
Developmental: similarities in embryonic form or developmental processes (eg, embryos of
human, chicken, cat)
Structural: similarity in adult features (eg, neck bone structure shared between giraffes and
humans)
What is the difference between acclimatization and adaptation? - ANS Acclimatization:
organism's response to the environment
Adaptation: heritable trait that increases the fitness of an individual. Acclimatization does not
change alleles, therefore it is not heritable.
How are the Galapagos finches an example of directly observed evolution? - ANS Beak
morphology and body size is heritable, and changes due to the environment. Since evolution =
∆ in allele frequencies, selection for deeper beaks kills medium beaks. ∆ in food source selects
for smaller beaks, which changes allele frequencies again.
How does the Galapagos finches exhibit non-Lamarckian evolution? - ANS Lamarckian
evolution says evolution is goal directed. Bidirectional evolution (deeper to smaller) goes
against this; if it was goal, it would've gone in a single direction.
`Provide examples where evolution is not goal-directed - ANS - Parasites lose complex
digestive systems
2 @COPYRIGHT THEBRIGHT 2025/2026
,- Finch beaks get larger, then smaller
Why can humans not fly? What constraints are in place? - ANS - Historical constraints: since
all traits come from previous traits, if we don't have a prior trait for flying, we won't develop
flight
- Genetic: we lack the necessary genes that would give us wings, flight, etc.
Individuals with genotype XX have same phenotype as genotype XY. Which allele is dominant,
and what are individuals with intermediate phenotypes called? - ANS X is dominant, Y is
recessive. Incompletely dominant.
What is evolution driven by? Of the four, which one introduces new alleles? - ANS Natural
selection, gene flow, genetic drift, mutation. Mutation is the only one that introduces new
alleles into populations (other than gene flow)
For a given population, there is more observed heterozygotes than predicted in HWE. What are
some reasons this might occur? - ANS - Non-random mating → subconsciously prefer
heterozygotes
- Natural selection → heterozygotes have an advantage over homozygotes (higher fitness)
In order for HWE to proceed, what assumptions must be made? - ANS - random mating →
gametes combine randomly
- no natural selection → parent generation survives and donates gametes
- no genetic drift → population is infinitely large **why does genetic drift affect small
populations?
- no gene flow → no alleles lost by migration
- no mutation → no new alleles
Why is low genetic variation bad? - ANS If pathogen comes and affects those certain alleles,
it can eradicate entire population since no individuals will be able to survive and reproduce.
3 @COPYRIGHT THEBRIGHT 2025/2026
, How might a population come under directional selection? - ANS - Facing selection to
develop characteristics that reinforce sexual isolation
- Develop traits that provide edge over competing species for resources
Obese babies can have trouble breathing, while tiny babies are prone to pneumonia and other
complicating affectations. What type of selection are babies likely under? - ANS Stabilizing
selection → selection for intermediate phenotype, elimination of extremes
How can inbreeding lead to accelerated natural selection? - ANS Inbreeding often results in
deleterious recessive alleles. Recessive alleles are under purifying selection
What can cause a species living in sympatry to diverge? What must it overcome? -
ANS Disruptive selection, gene flow
What might occur if the offspring of two parents with differing phenotypes is shown to have
low fitness? - ANS - Selection for less heritability
- Selection for reinforcement (extreme)
Is genetic drift adaptive? - ANS Drift can lead to adaptation, but it is not adaptive (i.e. cause
of natural selection). Drift is RANDOM with respect to allele frequency change
Why is genetic drift more prominent in small populations? - ANS Alleles can drift to fixation
or deletion in fewer generations. Law of averages only applies to large quantities.
How can two similar populations display two entirely different phenotypes? - ANS - Founder
effect → small group from source colonizes new area, with different allele frequencies than
source population
- genetic drift leads to random increase/decrease in certain alleles (more prominent in small
populations)
4 @COPYRIGHT THEBRIGHT 2025/2026
QUESTIONS AND ANSWERS
Why might Pasteur's experiment be inconclusive? - ANS The swan-necked flask broth may
not support cell growth, or the broth was poisoned. Experiment did not confirm hypothesis that
all cells come from pre-existing cells
Why are replicates important in experiments? - ANS To ensure that results were not
achieved by random chance
What is the definition of a replicate? - ANS Unit that shares a common thing (4 mice in one
cage = 1 replicate)
What does the law of succession suggest? - ANS As one species disappears, a similar one
appears. Suggests ancestors and descendants
What is the difference between vestigial traits and transitional features? - ANS vestigial -
useless features similar to useful features in related species (eg, coccyx in humans, tail in
monkeys)
transitional - intermediate feature seen in fossil species, between ancestral and descended
species (eg, aquatic animal fins, tetrapod limbs)
List potential outcomes of the bottleneck effect - ANS - Potential high frequency of
deleterious alleles that were previously at low frequency in source population
- Different allele frequencies from source population, could lead to speciation
1 @COPYRIGHT THEBRIGHT 2025/2026
,- Strong genetic drift due to small population size
Explain how the tuberculosis bacteria underwent natural selection during and after drug
therapy - ANS Variation: different strains → some resistant to drugs, some died
Heritability: drug-resistant bacteria passed drug-resistant gene to daughter cells
Differential fitness: bacteria that survived produced offspring
Selection: drug-resistant allele had higher chance of survival through drug therapy
Give three types of homologies. Provide an example for each - ANS Genetic: similarity in
RNA, DNA, amino acids (eg, AUG start codon shared with many living organisms)
Developmental: similarities in embryonic form or developmental processes (eg, embryos of
human, chicken, cat)
Structural: similarity in adult features (eg, neck bone structure shared between giraffes and
humans)
What is the difference between acclimatization and adaptation? - ANS Acclimatization:
organism's response to the environment
Adaptation: heritable trait that increases the fitness of an individual. Acclimatization does not
change alleles, therefore it is not heritable.
How are the Galapagos finches an example of directly observed evolution? - ANS Beak
morphology and body size is heritable, and changes due to the environment. Since evolution =
∆ in allele frequencies, selection for deeper beaks kills medium beaks. ∆ in food source selects
for smaller beaks, which changes allele frequencies again.
How does the Galapagos finches exhibit non-Lamarckian evolution? - ANS Lamarckian
evolution says evolution is goal directed. Bidirectional evolution (deeper to smaller) goes
against this; if it was goal, it would've gone in a single direction.
`Provide examples where evolution is not goal-directed - ANS - Parasites lose complex
digestive systems
2 @COPYRIGHT THEBRIGHT 2025/2026
,- Finch beaks get larger, then smaller
Why can humans not fly? What constraints are in place? - ANS - Historical constraints: since
all traits come from previous traits, if we don't have a prior trait for flying, we won't develop
flight
- Genetic: we lack the necessary genes that would give us wings, flight, etc.
Individuals with genotype XX have same phenotype as genotype XY. Which allele is dominant,
and what are individuals with intermediate phenotypes called? - ANS X is dominant, Y is
recessive. Incompletely dominant.
What is evolution driven by? Of the four, which one introduces new alleles? - ANS Natural
selection, gene flow, genetic drift, mutation. Mutation is the only one that introduces new
alleles into populations (other than gene flow)
For a given population, there is more observed heterozygotes than predicted in HWE. What are
some reasons this might occur? - ANS - Non-random mating → subconsciously prefer
heterozygotes
- Natural selection → heterozygotes have an advantage over homozygotes (higher fitness)
In order for HWE to proceed, what assumptions must be made? - ANS - random mating →
gametes combine randomly
- no natural selection → parent generation survives and donates gametes
- no genetic drift → population is infinitely large **why does genetic drift affect small
populations?
- no gene flow → no alleles lost by migration
- no mutation → no new alleles
Why is low genetic variation bad? - ANS If pathogen comes and affects those certain alleles,
it can eradicate entire population since no individuals will be able to survive and reproduce.
3 @COPYRIGHT THEBRIGHT 2025/2026
, How might a population come under directional selection? - ANS - Facing selection to
develop characteristics that reinforce sexual isolation
- Develop traits that provide edge over competing species for resources
Obese babies can have trouble breathing, while tiny babies are prone to pneumonia and other
complicating affectations. What type of selection are babies likely under? - ANS Stabilizing
selection → selection for intermediate phenotype, elimination of extremes
How can inbreeding lead to accelerated natural selection? - ANS Inbreeding often results in
deleterious recessive alleles. Recessive alleles are under purifying selection
What can cause a species living in sympatry to diverge? What must it overcome? -
ANS Disruptive selection, gene flow
What might occur if the offspring of two parents with differing phenotypes is shown to have
low fitness? - ANS - Selection for less heritability
- Selection for reinforcement (extreme)
Is genetic drift adaptive? - ANS Drift can lead to adaptation, but it is not adaptive (i.e. cause
of natural selection). Drift is RANDOM with respect to allele frequency change
Why is genetic drift more prominent in small populations? - ANS Alleles can drift to fixation
or deletion in fewer generations. Law of averages only applies to large quantities.
How can two similar populations display two entirely different phenotypes? - ANS - Founder
effect → small group from source colonizes new area, with different allele frequencies than
source population
- genetic drift leads to random increase/decrease in certain alleles (more prominent in small
populations)
4 @COPYRIGHT THEBRIGHT 2025/2026
