Transcript Day 4 Slides

Biological Species Concept
• “Species are groups of interbreeding
natural populations that are
reproductively isolated from other such
groups”
- Ernst Mayr, 1940
• reproductive isolation: genetic
differences preventing successful
interbreeding
1
Species on Earth
• # species on Earth today: ~3-50 million
• # of species that ever lived: ~75-2500
million
• It has been estimated that ~99% of all
species that have ever lived are extinct
2
Speciation
• Speciation
– the process by which one species splits
into two or more species
• How?
– Subgroups of the species become
reproductively isolated
• Classes of reproductive isolation
– Prezygotic: prevents zygote formation
– Postzygotic: prevents survival or
reproduction of offspring
3
Classes of speciation
• Allopatric
– geographic
separation
• Parapatric
– divergence across
a continous habitat
• Sympatric
– No separation
4
“Female Fickleness May Split a Species”
• NY females prefer males
with bright yellow bibs
• WI females prefer males
with large black masks
• When mixed, preferences
stayed the same
Source: Matt Kaplan, ScienceNOW Daily News, 11/30/2007
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Transitional fossils
• Fossils of organisms
with morphological
features intermediate
between those of an
ancestral species and
its descendants
?
7
Fish to tetropods
385-359 million
years ago
Tiktaalik
Discovered in 2004 on
Ellesmere Island, Canada.
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Dinosaurs to Birds
150 Million
years ago
Archaeopteryx
9
Land mammals to sea mammals
Source: evolution.berkeley.edu
10
Fossil DNA
ancient DNA
…CAATGACGTTAGCATGAG…
• Remnants in a
present-day genome
of previously
functional DNA that
“eroded” due to an
accumulation of
…GAATGGCGTAAGCCTGAG…
mutations
present-day DNA
11
Human chromosome 2: A fusion
Human chromosome 2
Remnants of old centromere
Remnants of old telomeres
Chimp chromosomes 2q and 2p
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