MCAT Biology Exam Latest Updated 2024 With Complete Solutions

MCAT Biology Exam Latest Updated 2024 With Complete Solutions Natural selection (types) Different types of selection lead to changes in phenotype: 1) Stabilizing selection 2) Directional selection 3) Disruptive selection 4) Adaptive selection Stabilizing selection Keeps the phenotypes in a narrow range, excluding extremes. Directional selection Moves the average phenotype toward one extreme. Disruptive selection Moves toward two different phenotypes at the extremes and can lead to speciation. Adaptive radiation The rapid emergence of multiple species from a common ancestor, each which occupies its own ecological niche. Species The largest group of organisms capable of breeding to form a fertile offspring. 1) Reproductively isolated from each other by pre- and post zygotic mechanisms. Pre zygotic mechanisms Prezygotic reproductive isolation Ecological, Temporal, Behavioral, Mechanical, Gametic Isolation when 1 species is separated, different evolutionary pressures leads to isolation, in which the progeny of these populations can no longer interbreed Post zygotic mechanisms Postzygotic reproductive isolation Hybrid inviability, sterility Evolution (types) 1) Divergent evolution 2) Convergent evolution 3) Parallel evolution Divergent evolution Occurs when two species sharing a common ancestor become more different. Convergent evolution Occurs when two species not sharing a recent ancestor evolve to become more similar due to analogous selection pressures. Parallel evolution Occurs when two species sharing a common ancestor evolve in similar ways due to analogous selection pressures. Molecular clock model States that the degree of difference in the genome between two species is related to the amount of time since the two species broke from a common ancestor.