Chapter 23: Species and their Formation (Part I & II)

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Chapter 23: Species and their Formation
Mar 10/2011
What are Species?
๎€Speciation: the process by which one species splits into two or more daughter
species
๎€Occurs gradually, and through a time line, you can tell where the distinction
happens
๎€Species = kinds
o1. Morphological Species Concept:
๎€Recognize species by their appearance (Darwin did this)
๎€Share alleles
๎€Binomial system of nomenclature (genus names ex: homosapiens)
๎€Did not recognize offspring differences and male/female differences
o2. Biological Species Concept:
๎€Species are groups of actually and potentially interbreeding natural
populations which are reproductively isolated from other such
groups
โ€ขIndividuals in a population can mate with each other but not
with those of another population
โ€ขThey are distinct evolutionary unit within which genes
recombine
How do new species arise?
๎€Species sometimes change by adapting to the changes in their environment
๎€If a species becomes isolated into 2 populations, within each isolated gene pool,
allele and genotype frequencies change and result of evolutionary mechanisms
๎€They no longer can interbreed once the barrier is removed
๎€HOW?
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oAllopatric speciation: physical barrier between species
๎€Dominant mode of speciation
๎€Allopatric species can occur through vicariant event and dispersal
(recall chapter 22)๎€‚finches that Darwin evaluated dispersed and did
not interbreed
oSympatric Speciation: does not require physical isolation
a.Ecological Isolation: different resources or different niches.
๎€ƒThrough disruptive selection, exploiting a new niche ๎€‚๎€„
reduces gene flow
๎€ƒReproduction is isolated because the species are ecologically
isolated
b.Polyploidy
๎€ƒDuplication of the whole set of chromosomes
๎€ƒMost arise through hybridization by self-fertilization
(flowering plants and ferns)
๎€ƒAuto-polyploidy: chromosome duplication in a single
species
๎€ƒOccurs if a cell accidentally duplicated the chromosomes,
resulting in a tetraploid individual.
i.Do not synapse properly with diploids because it has
odd numbers of chromosomes
๎€ƒAllo-polyploidy: combining of chromosomes from two
species ๎€‚ result of two related species that mate
Mar.15/2011-conโ€™t
What happens when newly formed species come together?
๎€Reproductive isolation evolves as an incidental by-product of genetic changes in
allopatric populations
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Document Summary

speciation: the process by which one species splits into two or more daughter species. occurs gradually, and through a time line, you can tell where the distinction happens. recognize species by their appearance (darwin did this) binomial system of nomenclature (genus names ex: homosapiens) did not recognize offspring differences and male/female differences: 2. species are groups of actually and 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 distinct evolutionary unit within which genes recombine. species sometimes change by adapting to the changes in their environment. If a species becomes allele and genotype frequencies change and result of evolutionary mechanisms isolated into 2 populations, within each isolated gene pool, They no longer can interbreed once the barrier is removed. how? www. notesolution. com: allopatric speciation: physical barrier between species.

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