Transcript Population and Speciation

Population and Speciation
Population Genetics: The study
of Evolution from a genetic point
of view.
Variations of Traits
• Biologists measure traits in large samples when
studying variation.
• Bell curves show that average populations have
similar traits. A few display the extremes of a
trait.
• Varying genotypes arise in 3 ways
– Mutations from flawed copies of genes
– Recombination from an independent assortment of
genes during meiosis
– Random fusion of gametes, combination of one sperm
and one egg.
Allele Frequency and the Gene Pool
• Gene pool: the total genetic information
available to a population
• Allele frequency: determined by dividing the
number of a certain allele by the total number
of alleles of all types in a population.
• Phenotype frequency: The number of
individuals with a certain phenotype divided
by the total number of individuals in a
population.
Harvey-Weinberg Genetic Equilibrium
based on an ideal hypothetical population not
evolving- This is not real life
• 1. no net mutations occur
• 2. individuals neither enter or leave a
population
• 3. The population is large
• 4. individuals mate randomly
• 5. Selection does not occur
Requirements for Genetic Equilibrium.
Mutation:
• Mutation: spontaneous mutation is slow over
a longer period of time
• Mutagens force mutations from chemical or
radiation exposure
• They produce new alleles that may be harmful
or beneficial to a population
Migration
• Immigration: the movement into a population
• Emigration: the movement out of a population
• Gene Flow: the process of genes moving from
one population to another.
Genetic Drift
• The phenomenon by which allele frequencies
in a population change as a result of random
events or chance.
• Small populations experience a large amount
of drift, they lose genetic diversity
• Large populations maintain a small amount of
genetic drift
Nonrandom Mating
• Random mating doesn’t always occur in a
population because of geographic proximity
• Nonrandom mating is selection which may
result in genes being to similar, which cause
genetic disorders in a population
• Selection of a mate based on similar
characteristics is assortative mating
Natural Selection
• Members of a species more likely to pass on their genes to
the next generation
• Stabilization selection: individuals with average form of a trait
have the highest fitness
• Directional selection: individuals that have a more extreme
form of a trait have a greater fitness than those with average
form of a trait.
• Disruptive selection: individuals with extreme variation have
greater fitness than the average form of a trait.
• Sexual selection: Males must be selected by females based on
traits that are desired. The genes of successful reproducers
not just survivors are amplified through natural selection.
Concept of Species
• Speciation: Some species are very similar to
their ancestral species while other
populations become quite different
• Morphology: the internal and external
structure and appearance of an organism
• Biological species concept: a species is a
population of organisms that can successfully
interbreed but can not breed with other
groups.
Isolating Mechanisms
• Geographic isolation: physical separation
• Reproductive isolation: barriers to successful
breeding between groups in the same area.
• Broad type: prezygotic-before fertilization and
postzygotic-after fertilization
Rates of Speciation
• Speciation may take millions of years, some
may occur more rapidly, it may not occur
smoothly and gradually.
• Punctuated equilibrium: a sudden shift in
form that is often seen in the fossil record.