BIOL 101 Chapter Notes - Chapter 24: Meiosis, Reproductive Isolation, Allele Frequency

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17 Sep 2016
Chapter 24: The Origin of Species
speciation the process by which one species splits into two or more species
microevolution changes over time in allele frequencies in a population
macroevolution the broad pattern of evolution above the species level
biological species concept a species is a group of populations whose members have potential
to interbreed in nature and produce viable, fertile offspring - but do not produce viable offspring
with members of another species
species united by reproductively compatibility
reproductive isolation the existence of biological factors (barriers) that impede members of
two species from interbreeding and producing viable, fertile offspring
barriers block gene flow between the species and limit creating of hybrids (offspring
from interspecific mating)
Prezygotic Barriers (before the zygote) blocks fertilization from occurring impede mating or
hinder fertilization after mating does occur
impedes members of different species from attempting to mate by preventing an
attempted mating from being completed successfully
if sperm cell overcomes prezygotic barriers there are postzygotic barriers
Habitat Isolation species occupying different habitat will rarely encounter each other
because isolated by physical barriers i.e. mountain range etc.
Temporal Isolation species that breed during different times of the day, different
seasons, or different years can not mix their gametes
Behavioral Isolation courtship rituals are specific to a species and do not enable
different species to identify potential mates of other species
Mechanical Isolation mating is attempted but morphological differences prevent its
successful completion
Gametic Isolation sperm of one species cannot fertilize the egg of another species
Postzygotic Barriers (after the zygote reproductive isolation after the hybrid zygote is formed
problems after birth may leave hybrid infertile or decrease their chance of survival
Reduced Hybrid Viability genes of different parent species may interact in ways that
impair the hybrids development or survival in the environment
Reduced Hybrid Fertility hybrids may be able to survive but they are infertile. If
chromosomes of two parent species differ in number or structure meiosis in the hybrids may fail
to produce normal gametes. Since hybrid cannot produce offspring when they mate w/ either
parent species, genes cannot flow freely between species
Hybrid Breakdown some first generation hybrids are viable and fertile but when they
mate, offspring are feeble or sterile
Morphological Species Concept characterizes a species by body shape and structural
applied to asexual and sexual organisms
useful even w/o info on gene flow
disadvantage: relies on subjective criteria; researchers may disagree of structural
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