Download Natural Selection

Natural Selection
and
Speciation
Natural Selection
• Basis for Darwinism
• Brings about the evolution of new
species of animals and plants
• Individuals in a population less
adapted to their environment are
less likely to survive
• Disease, competition, and other
forces acting on the population
eliminate the weak
• Survivors pass on any heritable
advantageous characteristics
Adaptive Radiation = the
diversification of a group of
organisms into forms filling
different ecological niches.
Evolutionary Fitness
• The probability that the line of
descent from an individual with a
specific trait will not die out.
• Determined by overall
population numbers
• Lower Genetic Diversity
• Not related to the lifespan of
individuals in the population
Zygotic Barriers
• Prevent different species from
sharing DNA and producing
offspring
Prezygotic vs. Postzygotic
Barriers
The zygote forms when sperm and egg
combine - fertilization. So
mechanisms that prevent two
organisms from mating would be
prezygotic because they prevent
sperm and egg from meeting.
Postzygotic mechanisms are ones that
make the zygote nonviable or the
offspring sterile or other mechanisms
that occur after fertilization takes
place
Hardy-Weinberg
Equilibrium
A principle stating that the genetic
variation in a population will
remain constant from one
generation to the next in the
absence of disturbing factors.
http://www.youtube.com/watch?v=ikqXvajKU08
5 Requirements for
the Hardy-Weinberg
Equilibrium
• ___________________________
• ___________________________
• ___________________________
• ___________________________
• ___________________________
Equations
• Allele Frequency: ____________
• Genotype Freq.:_____________
• Homozygous Dom. (BB):______
• Heterozygous Dom. (Bb):______
• Homozygous Rec. (bb):______
New traits in organisms can
only appear immediately as
a result of changes in the
DNA!!!
Scientific evidence supports the
evolution of all species including
extinct organisms.
Other Key Terms/Concepts
• Genetic Diversity - the total
number of genetic characteristics in
the genetic makeup of a species
• Mutation - occurs when a DNA gene
is damaged or changed in such a way
as to alter the genetic message
carried by that gene
• Allele - an alternative form of a gene
(one member of a pair) that is located
at a specific position on a specific
chromosome
• Adaptation - any alteration in the
structure or function of an organism
or any of its parts that results from
natural selection and by which the
organism becomes better fitted to
survive and multiply in its
environment
• Relative Fitness - how successful an
organism has been at passing on its
genes. The more likely that an
individual is able to survive and live
longer to reproduce, the higher is the
fitness of that individual. (Often
expressed in a %)
• Speciation - The evolutionary
formation of new biological species,
usually by the division of a single
species into two or more genetically
distinct ones
• Divergence - The evolutionary
tendency or process by which animals
or plants that are descended from a
common ancestor evolve into
different forms when living under
different conditions
• Polyploidy - Having one or more
extra sets of chromosomes and results
in rapid evolution
Reproductive Isolation - the
inability of a species to breed
successfully with related species due to
geographical, behavioral, physiological,
or genetic barriers or differences
Factors that impact the survival of
organisms in a rapidly changing
environment:
• Gene mutations are present in
the gene pool
• All of the alleles in the population
are diverse and varied
• Changes are usually the result of
extreme environmental variations
• Organisms generally adapt at the
same rate as the environmental
change
Effects on the
evolutionary process…
• Chance and random events (but
not in the form of natural
selection)
• Found in all populations
• Most common in small
populations
• Not determined by the size of the
population