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BIOA02H3 (153)
Chapter 23

Chapter 23

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Department
Biological Sciences
Course Code
BIOA02H3
Professor
Kamini Persaud

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Chapter 23 Speciation
Species
-(1) literally means kinds
-Carolus Linaeus originated the binomial system of Latin nomenclature by which species are known today; since
he knew nothing of genetics and mating behaviour of the organisms, he classified them based on their appearance
which is called the MORPHOLOGICAL SPECIES CONCEPT
-(2) not all members of a species must look alike: information other than appearance is used to decided whether
distinguished individuals are members of the same or different species
-(3) species are likebranches of trees”: each species has a history that starts at a speciation event and ends at
either extinction or another speciation event
-SPECIATION the process by which one species splits into two or more daughters species, which thereafter
evolve as different lineages; this process is often gradual and guarantees that in many cases, two populations at
various stages in the process of becoming new species will exist
REPRODUCTIVE ISOLATION an important component of the process of speciation: if individuals of
a population mate with one another, but not with individuals of another populations, they constitute a
distinct group within genes recombine (that is, separatebranches on the tree of life)
-Ernst Mayr proposed the definition of species known as the BIOLOGICAL SPECIES CONCEPT: (4) species are
groups of “actually andpotentially interbreeding natural populations which are reproductively isolated from
other such groups
actually says that the individuals live in the same area and interbreed with one another
potentially says that although the individuals do not live in the same area, and therefore cannot
interbreed, other information suggests that they would do so if they did get together
* this definition does not apply to organisms that reproduce asexually *
Speciation Barriers (Mode of Speciation)
-speciation requires that gene flow within a population whose members formerly exchanged genes be interrupted;
gene flow can be interrupted in two major ways, each of which characterizes a mode of speciation:
Allopatric Speciation (Geographic Speciation)
allo, “different; patris, “country; speciation that results when a populations is divided by a
physical barrier
the dominant mode of speciation among most organisms
ex: bodies of water, mountain ranges, continental drifts, rise of sea levels, glacier movements,
climate change
may also result when some members of a population cross and existing barrier and found a new
isolate population (ex: Darwins finches in the Galapagos)
may also result to FOUNDER EVENTS: the founding of new populations by individuals
dispersing among the islands (ex: fruit-fly Drosophilia in the Hawaiian Islands)
a physical barriers effectiveness at preventing gene flow depends on the size of and mobility of
the species in question (ex: snails crossing a highway versus birds)
Sympatric Speciation
sym, together with; a partition of a gene pool without physical isolation
sympatric speciation via ecological isolation is widespread among insects which feed on only a
single plants species (ex: Rhagoletis flies with hawthorn fruits versus apples)
POLYPLOIDY the production within an individual containing duplicate sets of chromosomes;
the most common means of sympatric speciation
polyploidy can arise either from chromosome duplication in a single species
(AUTOPOLYPLOIDY) or from the combining of the chromosomes of two different species
(ALLOPOLYPLOIDY)
an autopolyploid individual originates when cells that are normally diploid accidentally
duplicate their chromosomes, resulting in a tetraploid (four sets of chromosomes)
individual; tetraploid individuals cannot produce viable offspring by mating with a
diploid individual but it can do so with if it self-fertilizes or mates with another
tetraploid
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Description
Chapter 23 Speciation Species - (1) literally means kinds - Carolus Linaeus originated the binomial system of Latin nomenclature by which species are known today; since he knew nothing of genetics and mating behaviour of the organisms, he classified them based on their appearance which is called the MORPHOLOGICAL SPECIES CONCEPT - (2) not all members of a species must look alike: information other than appearance is used to decided whether distinguished individuals are members of the same or different species - (3) species are like branches of trees: each species has a history that starts at a speciation event and ends at either extinction or another speciation event - SPECIATION the process by which one species splits into two or more daughters species, which thereafter evolve as different lineages; this process is often gradual and guarantees that in many cases, two populations at various stages in the process of becoming new species will exist REPRODUCTIVE ISOLATION an important component of the process of speciation: if individuals of a population mate with one another, but not with individuals of another populations, they constitute a distinct group within genes recombine (that is, separate branches on the tree of life) - Ernst Mayr proposed the definition of species known as the BIOLOGICAL SPECIES CONCEPT: (4) species are groups of actually and potentially interbreeding natural populations which are reproductively isolated from other such groups actually says that the individuals live in the same area and interbreed with one another potentially says that although the individuals do not live in the same area, and therefore cannot interbreed, other information suggests that they would do so if they did get together * this definition does not apply to organisms that reproduce asexually * Speciation Barriers (Mode of Speciation) - speciation requires that gene flow within a population whose members formerly exchanged genes be interrupted; gene flow can be interrupted in two major ways, each of which characterizes a mode of speciation: Allopatric Speciation (Geographic Speciation)
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