Transcript Formation of Species Section 16-3

Disruption of Genetic Equilibrium
Section 16-2
Mutation
• A mutation is a change in the nucleotidebase sequence a DNA molecule.
Population and Gene Movement
• Gene flow is the movement of alleles into
or out of a population.
• It may take place in two ways:
– Immigration
• the movement of individuals into a population
– Emigration
• the movement of individuals out of a population
Gene Flow
Genetic Drift
• When allele frequencies in a population
change from random events, or chance.
Comparing the Effects of Random
and Nonrandom Mating
• Random mating is mating without caring
about phenotypic traits or genetic makeup.
• Nonrandom mating is driven by choosing
mates that have a particular attractive
characteristic.
apple maggot flies
apples
hawthorns
Gene flow has been reduced between flies that feed
on different food varieties, even though they both
live in the same geographic area.
• If the insect is only
attracted to the
white flower, then
only that flower will
reproduce.
Sexual Selection
• When females tend to
choose the males they
mate with based on
certain traits.
• Female peacocks
seem to prefer
extravagant tail
feathers.
Stabilizing Selection
• Individuals with the average form of a trait
have the highest fitness.
Disruptive Selection
• Individuals with either extreme variation of a
trait have greater fitness than individuals with
the average form of the trait.
Directional Selection
• Individuals that display an extreme form of a
trait have greater fitness than individuals with
an average trait.
Formation of Species
Section 16-3
Speciation
• species formation in closely
related species
• Some are very similar to their
relatives whereas others look
quite different.
Morphological Concept of Species:
– Physical characteristics (internal and external)
– Limitations:
• Example: Red tail monkeys have different facial features but
are still the same species
The Biological Species Concept
• Proposed by Ernst Mayr (1904-2005)
• A species is:
– A population of organisms that can successfully
interbreed but cannot breed with other groups.
• Limitations:
– Cannot be applied on organisms that are extinct.
– Cannot be used for organisms that reproduce
asexually.
What is a species?
• A single kind of organism that is similar in
morphology and can interbreed to produce
fully fertile offspring.
Geographic Isolation
• Physical separation of populations due to
geographic barriers that prevent interbreeding.
• Gene flow between the two groups stops
• Natural selection and genetic drift cause the
groups to diverge causing allopatric
speciation.
Allopatric Speciation
Allopatric speciation
Reproductive Isolation
• Genetic barriers that prevent populations
found in the same place from breeding.
Two types:
• Prezygotic (premating): prevents
fertilization.
• Postzygotic (postmating): prevents
offspring from reproducing.
Prezygotic barrier
• Prevents reproduction before fertilization.
• Isolation occurring after fertilization.
Mule
Zorse
Liger
Rates of Evolution
1. Punctuated equilibrium is
when we see a big change
and then no change for a long
period of time.
•
Looks like a “stair case”.
2. Gradualism is
constant change
over a period of
time.
References
• http://faculty.etsu.edu/yampolsk/speciation.jpg
• http://www.jpowerphotography.com/gallery/images/other/img-rabbitlg.gif
• http://www.astronomy-images.com/dayimages/California/jackrabbit.200307.jpg
• http://www.rsnz.org/directory/yearbooks/2005/Mayr-obit.jpg
• http://a.abcnews.com/images/Politics/pd_polar_bear_080117_ms.jp
g
• http://english.people.com.cn/mediafile/200802/01/P20080201112139
2544312484.jpg
• http://msnbcmedia2.msn.com/j/msnbc/Components/Photo_StoryLev
el/071112/071112_sunbear_hmed_10a.hmedium.jpg
• http://taxonomy.zoology.gla.ac.uk/~rdmp1c
/teaching/L1/Evolution/l6/grandcanyon.gif