Transcript Genetics and Evolution

Genetics and Evolution
Genetics and Evolution
• Populations evolve, NOT individuals!
• Evolution = changes in a population’s genes
over time
Vocabulary
• Gene pool = a collection of all of the possible
genes in a population
• Allelic frequency = the % of an allele in a gene
pool
• Genetic equilibrium = occurs when allele
frequency does not change (NO EVOLUTION!)
Genetic equilibrium
• So what are some ways that the genetic
equilibrium changes?
1. mutation
– most mutations are lethal and those organisms do
not survive
– occasionally a mutation results in a useful
variation and the new gene is selected for
Genetic equilibrium
• So what are some ways that the genetic
equilibrium changes?
2. genetic drift
– chance events alter the gene pool
– usually affects smaller populations
– Ex. Amish population of 12,000 carries a recessive
allele that results in short arms and legs and extra
fingers and toes
Genetic equilibrium
• So what are some ways that the genetic
equilibrium changes?
3. migration
- transport of genes to and from a population
Genetic equilibrium
• So what are some ways that the genetic
equilibrium changes?
4. natural selection
– most significant effect on genetic equilibrium
Natural Selection can Change the
Genetic Equilibrium in 3 Ways
Changes in genetic equilibrium
1. Stabilizing Selection:
– favors the average form
of a trait
– results in less variation in
a population
– Ex: average sized spiders
Changes in genetic equilibrium
2. Directional Selection
– favors one extreme form
of a trait
– results in species
showing one extreme
form of a trait
– Ex: woodpeckers with
long beaks
Changes in genetic equilibrium
3. Disruptive Selection
– favors both extreme
forms of a trait
– can result in 2 new
species over a long
period of time
– Ex: light and dark limpets
Evolution of a new species
• Speciation = the
evolution of a new
species (when
interbreeding is
prevented)
What leads to speciation?
1. Geographic isolation
EX: Tree frog
population with a river
separating them
What leads to speciation?
2. Reproductive isolation
– EX: Genetic- genetic material becomes so different
that fertilization can’t occur
– EX: Behavioral- one pop of frogs mates in the fall,
the other in the spring
What leads to speciation?
3. Change in chromosome
number (polyploidy)
– EX: nondisjunction
occurs during meiosis
leaving the zygote (4n)
instead of 2n; wheat,
cotton, and apples are
examples
– Only takes one
generation to create a
new species
Speciation rates
1. Gradualism: a new
species forms through a
gradual change of
adaptations
2. Punctuated equilibrium
a new species forms
quickly in bursts, with
long periods of genetic
equilibrium in between;
10,000 years or less
Patterns of evolution
1. Adaptive radiation: an ancestral species
evolves into a wide variety of species to
occupy their own niche or diverse habitat
EX: honeycreepers on the Hawaiian Islands
EX: Darwin’s finches on the Galapagos Islands
Patterns of evolution
2. Divergent Evolution: species that were similar
become different in order to adapt to different
environments (Adaptive radiation is a type of
divergent evolution)
Patterns of evolution
3. Convergent Evolution : species that were
unrelated evolve similar traits in order to
occupy similar environments in different parts
of the world
EX: pipe cactus and Euphorbia – both have
fleshy body type and no leaves to survive the
desert but totally unrelated