McMaster Bio 1M03 Exam Questions With Correct Answers

Why might Pasteur's experiment be inconclusive? - 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? - Answer To ensure that results were not achieved by random chance What is the definition of a replicate? - Answer Unit that shares a common thing (4 mice in one cage = 1 replicate) What does the law of succession suggest? - Answer As one species disappears, a similar one appears. Suggests ancestors and descendants What is the difference between vestigial traits and transitional features? - 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 - 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 - 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 Give three types of homologies. Provide an example for each - 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? - 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? - 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? - 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 - Answer - Parasites lose complex digestive systems - Finch beaks get larger, then smaller Why can humans not fly? What constraints are in place? - 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? - Answer X is dominant, Y is recessive. Incompletely dominant. What is evolution driven by? Of the four, which one introduces new alleles? - 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? - Answer - 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? - Answer - 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? - 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? - Answer - 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? - Answer Stabilizing selection → selection for intermediate phenotype, elimination of extremes How can inbreeding lead to accelerated natural selection? - 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? - Answer Disruptive selection, gene flow What might occur if the offspring of two parents with differing phenotypes is shown to have low fitness? - Answer - Selection for less heritability - Selection for reinforcement (extreme) Is genetic drift adaptive? - Answer 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? - Answer 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? - Answer - 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) How is gene flow an obstacle to speciation? - Answer Gene flow makes populations more similar → less chance for speciation (occurs in sympatry and allopatry) Which mechanisms of adaption increase diversity, and decrease? - Answer Increase → gene flow (recipient), mutation Decrease → genetic drift, natural selection (increase in certain alleles) What is implied about the alleles A and a if the genotype Aa has higher fitness than homozygotes? - Answer A and a are incompletely dominant Most mutations are __________________, some are __________________ - Answer Deleterious (purifying selection), beneficial (natural selection) How does sex affect allele frequency? - Answer Sex does not provide new alleles, but produces new combinations. Explain the fundamental asymmetry of sex - Answer Eggs are expensive, sperm are cheap Females invest more time into offspring, males invest more time into mating How does sexual selection affect males? - Answer Males with heritable traits that enhance their chance of mating are selected for. Selection acts stronger on males, since females' pickiness of mates makes them desirable to males. The development of flashy colours or special dances in males to attract mates is because... - Answer Males experience greater variation in reproductive success, therefore any traits that maximize their fitness are selected for Male gorillas are significantly larger than their female counterparts. Chimpanzees have larger genitals than gorillas. What do these two statements imply? - Answer Male gorillas fight each other for mating rights with a female (greater sexual dimorphism = greater sexual selection) Chimpanzees are social, and use their genitals to maximize fitness (mate often) What is the criteria for the biological species concepts? What are the advantages and disadvantages of this concept? - Answer Populations must be reproductively isolated (pre or post zygotic isolation). Pre zygotic is favoured, since there is less wasted effort (inviable offspring) Disadvantages → cannot apply to extinct, asexual species. Hard to determine closely related species if separated by distance What are the advantages and disadvantages of the morphological species concept? - Answer Advantages → fossil species, diverse groups Disadvantages → convergent or divergent evolution? Polymorphic species (sexual dimorphism)? Similar groups but inviable hybrids? Cryptic species (Morphologically identical, different traits)? What type of species is the ecological species concept applied to? - Answer Small things, like archaea, bacteria, asexual eukaryotes. Explain the relationship between genetic isolation and genetic divergence - Answer Lack of gene flow leads to genetic isolation. Isolation allows for genetic divergence, which reinforces for genetic isolation (pre-zygotic mechanisms, reinforcement) How do isolated populations diverge from another? - Answer Species in allopatry must overcome gene flow in order to diverge. They diverge because of natural selection (living in different environments) and genetic drift (different allele frequencies change over time → adaptive) What are the two methods of allopatric divergence? - Answer Vicariance → physical separation of habitat Dispersal → dispersal and colonization to a new area What are two methods of sympatric divergence? - Answer Disruptive selection → speciation based on favour of extreme phenotypes Chromosome mutations Polyploidy is a source of... - Answer New genetic material and genetic isolation What may happen if two similar species reunite in the same environment? How many species will result? - Answer Fusion: is differences are small or gene flow is strong → 1 Reinforcement: if hybrids have low fitness, pre-zygotic mechanisms will be selected for → 2 Exclusion: one species will outcompete other species → 1 Hybrid zones: area where interbreeding occurs, leading to gene flow → 1 (could be 2) New species: hybrids are better suited to environment than parental species → 1, 2, 3 (could outcompete parental species) What is the difference between cladistic and phenetic approaches? - Answer Cladistic: traits relative to time (derived, ancestral/basal) Phenetic: all traits considered equally, overall similarity between species What is an advantage of using morphological traits (compared to genetic)? - Answer Fossil species, rapidly evolving organisms (eg, viruses), not enough data for genetic What is the difference between convergent evolution and co-evolution? - Answer Convergent: independent evolution of similar traits due to adaptation in similar environments (eg, dolphins and ichthyosaurus) Co-evolution: evolution of one species encourages evolution of another (eg, plants evolve new ways to use insects for pollination) Explain the link between convergent evolution and homoplasy - Answer Homoplasies can be caused by convergent evolution → similar-looking traits evolve independently due to similar environments Dolphins are mammals while ichthyosaurus are reptiles. Both species have streamlined bodies, flippers, and fins. Analysis of phylogenetic trees show sister groups to both taxa do not have streamlined bodies, flippers, or fins. What does this suggest? - Answer Dolphins and ichthyosaurus are examples of (convergent) evolution by natural selection. Adaptation to hunting underwater developed streamlined bodies, even though they are not related. How does longer development periods encourage female-female bonding? - Answer Females form coalitions to care for young offspring, secure food, and to dominate males in a (bonobo) troop How did complex/adaptive foraging promote cooperation? - Answer - Male-female cooperation → primate child care not suited for hunting lifestyle - Cooperation between people with two different skills → gather food at different times - Cooperation between hunters → hunting success highly variable - Cooperation in teaching and learning → teaching young how to forage