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Chapter 23 Species and Their Formation Combination of Lecture and Textbook

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Department
Biological Sciences
Course Code
BIOA02H3
Professor
Kamini Persaud

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Chapter 23: Species and their Formation
23.1 What are species?
Species are the result of processes that unfold over time
Speciation: process by which one species splits into 2 or more daughter species
A species starts at a speciation event and ends either with extinction or another speciation event
(produces daughter species)
Happens gradually
Interbreeding populationGenetically different but reproductively compatible -Also
reproductively incompatible
The point at which daughter populations can be considered a different species depends how you
define distinct species
Species=different kinds
Defined in different ways
1) Morphological species concept:
Recognize most species by their appearance
Members look alike because they share alleles
Use binomial system of nomenclature…but we need something else because
some males and females of the same species look alike and sometimes parents
and offspring of same species do/dont look alike
2) Biology species concept:
Species are groups of actively or potentially interbreeding natural populations
which are reproductively isolated from other such groups
Individuals in a population can mate with each other but not with those of
another population
They are a distinct evolutionary unit within which genes recombine
First level daughter populations are morphologically distinct, second level
populations are morphologically and biologically distinct
23.2 How do new species arise:
www.notesolution.com
Not all evolutionary changes result in new species
Speciation occurs if evolutionary changes result in 2 or more daughter species
Genotype and allele frequencies change within each isolated gene pool and may change due to
action of evolutionary mechanisms
Speciation requires the gene flow within a population whose members formerly exchanged genes
be interrupted (2 ways)
1) Allopatric Speciation
Requires almost complete genetic isolation
When populations are separated by a physical barrier=geographic speciation
oThought to be dominant mode of speciation
Barriers due to continental drift, sea level changes, glaciers, climate, etc
Environments are different, populations evolve differently also
Can also occur is some individuals cross a barrier to form a new, isolated
population
Physical barriers effectiveness at preventing gene flow depends on size and
mobility of species in question
2) Sympatric Speciation: partition of gene pool
Ecological isolation:
oDifferent resources/different niches
oExploiting new resources/niche may automatically reduce gene flow with
individuals exploiting other niches
o=reproductively isolated because the populations are ecologically
isolatedthey feed on different resourcesi.e. in case of butterflies they
emerge from their pupae at different times=faster/slower
developmentwidespread among insects
Polyploidy:
oSympatric speciation most commonly occurs by polyploidy=duplication
of a whole set of chromosomes
www.notesolution.com

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Description
Chapter 23: Species and their Formation 23.1 What are species? Species are the result of processes that unfold over time Speciation: process by which one species splits into 2 or more daughter species A species starts at a speciation event and ends either with extinction or another speciation event (produces daughter species) Happens gradually Interbreeding populationGenetically different but reproductively compatible -Also reproductively incompatible The point at which daughter populations can be considered a different species depends how you define distinct species Species=different kinds Defined in different ways 1) Morphological species concept: Recognize most species by their appearance Members look alike because they share alleles Use binomial system of nomenclaturebut we need something else because some males and females of the same species look alike and sometimes parents and offspring of same species dodont look alike 2) Biology species concept: Species are groups of actively or potentially interbreeding natural populations which are reproductively isolated from other such groups Individuals in a population can mate with each other but not with those of another population They are a distinct evolutionary unit within which genes recombine First level daughter populations are morphologically distinct, second level populations are morphologically and biologically distinct 23.2 How do new species arise: www.notesolution.com
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