McMaster Bio 1M03: Exam 2024/2025 Questions with all
the correct Answers ;( Real actual exam) Why might Pasteur's experiment be inconclusive? - Correct Answer 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? - Correct Answer To ensure that results were not achieved by random chance What is the definition of a replicate? - Correct Answer Unit that shares a common thing (4 mice in one cage = 1 replicate) What does the law of succession suggest? - Correct Answer As one species disappears, a similar one appears. Suggests ancestors and descendants What is the difference between vestigial traits and transitional features? - Correct Answer 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 - Correct Answer - 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
- Strong genetic drift due to small population size
Explain how the tuberculosis bacteria underwent natural selection during and after drug therapy - Correct Answer 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 1 / 3
Give three types of homologies. Provide an example for each - Correct Answer 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? - Correct Answer 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? - Correct Answer 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? - Correct Answer 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 - Correct Answer - Parasites lose complex digestive systems
- Finch beaks get larger, then smaller
Why can humans not fly? What constraints are in place? - Correct Answer - 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? - Correct Answer X is dominant, Y is recessive.Incompletely dominant. 2 / 3
What is evolution driven by? Of the four, which one introduces new alleles? - Correct Answer 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? - Correct Answer - Non-random mating → subconsciously prefer heterozygotes
- Natural selection → heterozygotes have an advantage over homozygotes (higher fitness)
- 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
- Develop traits that provide edge over competing species for resources
- / 3
In order for HWE to proceed, what assumptions must be made? - Correct Answer - random mating → gametes combine randomly
Why is low genetic variation bad? - Correct Answer If pathogen comes and affects those certain alleles, it can eradicate entire population since no individuals will be able to survive and reproduce.How might a population come under directional selection? - Correct Answer - Facing selection to develop characteristics that reinforce sexual isolation
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? - Correct Answer Stabilizing selection → selection for intermediate phenotype, elimination of extremes How can inbreeding lead to accelerated natural selection? - Correct Answer 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? - Correct Answer Disruptive selection, gene flow