BI111 Lecture Notes - Lecture 4: Homologous Chromosome, Meiosis, Sympatric Speciation
BI111 – L4
Differential Fitness Species:
Species are groups of individuals that are reciprocally characterized by features that would have
negative effects in other groups and cannot be regularly exchanged between groups upon
contact
o“Opposite fitness effects” of alternative alleles
Differences may be due to differential adaptation, genetic drift, or other non-adaptive processes
(including polyploidism or infection by symbionts)
Defined by sets of traits based on selection
Pros:
oAllows exchange of genes (as long as they have no deleterious effect on fitness)
oRecognizes that species-specific features arise via reproductive isolation and differential
selection
oReproductive isolation is not necessary (“permeable” reproductive barriers)
oApplicable to uniparental and biparental organisms
Cons:
oCan only be used easily in extant (not extinct) populations
oNeed to know the fitness effects of trait variation
oHow to deal with lineages of individuals inhabiting the same environment but carrying
different selectively neutral alleles that are incompatible when combines in offspring?
Comparative Anatomy Reveals Different Phenotypes (adaptations?):
Lots of morphological differences between neanderthals
In a chunk of X chromosome found in some human contain genes that are involved in immune
responses and thought that humans living in Europe during that time gave them a selective
advantage
We might select against it now even though it used to be selective for
The “Species Concept” Problem:
Species are simultaneously reproductive communities, ecological entities, genetic entities and
evolutionary actors, each with their own unrepeatable history
Each species concept tells us part of the story of biodiversity
Trade-off between concepts that are universal vs. those that are specific
Species concept - a set of conditions that are necessary and sufficient to identify a group of
individuals as a species
oSpecies concepts do not only define what a species is, but in doing so, also define what
speciation is
Species and Speciation
How do species arise?
oSpontaneous vs. gradual processes
Why and where do they arise?
oAllopatry, parapatry, sympatry
What keeps them isolated from each other
oAdaptation, drift and divergence
Allopatric Speciation:
Most common/uncontroversial way that subdivided populations can speciate
Relies on geographic isolation
Interferes with gene flow → alleles that distinguishes each species merge together
Geographical barriers cause a single species to split into 2 different species
oReinforcement of ‘species barriers’ upon secondary contact
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Species are groups of individuals that are reciprocally characterized by features that would have negative effects in other groups and cannot be regularly exchanged between groups upon contact o. Differences may be due to differential adaptation, genetic drift, or other non-adaptive processes (including polyploidism or infection by symbionts) Defined by sets of traits based on selection. In a chunk of x chromosome found in some human contain genes that are involved in immune responses and thought that humans living in europe during that time gave them a selective advantage. We might select against it now even though it used to be selective for. Species are simultaneously reproductive communities, ecological entities, genetic entities and evolutionary actors, each with their own unrepeatable history. Each species concept tells us part of the story of biodiversity. Trade-off between concepts that are universal vs. those that are specific. How do species arise: spontaneous vs. gradual processes. Why and where do they arise: allopatry, parapatry, sympatry.
