Download Evolution (Genetic Change in Species Over Time) is a consequence

Evolution (Genetic Change in Species
Over Time) is a consequence of:
1. Genetic variation within a populationfrom mutation, recombination of genes
at fertilization, & crossing over during
meiosis)
2. More offspring are born than can survive
and reproduce
3. Competition for limited resources
4. Organisms with more favorable traits
survive and reproduce at a greater rate
than those with less favorable traits
The Current Definition Of
Evolution
• From a modern genetic perspective,
evolution is defined as a change in allele
frequencies from one generation to the
next.
• Allele frequencies are indicators of the
genetic makeup of an interbreeding group
of individuals known as a population.
Gene Pool-all of the
alleles for a given trait
of all of the individuals
in a population
Gene Frequency-the
frequency at which one
allele for a trait occurs
within the gene pool
Natural Selection- mechanism of
evolutionary change; discovered by Charles
Darwin and Alfred Wallace
1859
Changes in the frequencies of certain traits in
populations; traits that increase the survival and
reproductive success of individuals will increase within
the population over time; traits that decrease survival or
reproduction tend to decrease in frequency over time.
Natural Selection linked to
Environmental Change
Hypothesis: If
there is long
term
environmental
change
in one direction,
allele
frequencies
should
Selective Pressure =
also shift
predator
gradually
Adaptation =
each
camouflage coloration
generation
Genetic Principles
Discovered by Gregor Mendel
1882-1884
• Darwin unaware of Mendel’s work
• Mendel’s conclusions about heredity
support Darwin’s explanation for species
change over time
Adaptation-process by which species
becomes better suited for life in its
environment Whence Whales?
•response of
populations to
environmental
change
• results from
natural selection
•caused by increase
in frequency of
alleles for beneficial
traits
Which group of
ancient mammals
gave rise to
whales?
DNA, fossils &
morphological
evidence
suggests is was
the artiodactlys
(includes modern
hippos, camels,
pigs, & ruminants)
Whale Evolution
Ancient populations of
artiodactyls adapted to
various environments
The hippototimus is probably
the closest living relative of
modern whales.
Models of Evolution
1. Gradualismgradual
genetic
change over
long periods
of time leads
to new species
2. Punctuated
equilibriumperiods of
rapid genetic
change in
species is
separated by
periods of
stability
Homologous Structures
A similar structure in two organisms can be
found in a common ancestor.
Molecular Homologies
• DNA: The universal genetic code is stored
in DNA for all life forms
• Amino Acids: All organisms build
themselves from the same 20 amino acids
• Cell Organelles: Evidence suggests that
chloroplasts and mitochondria are
descended from bacteria
Lamarck’s Idea of Acquired
Characteristics Replaced by Natural
Selection
18th Century Scientist: Jean Babtist
Lamarck the first to state that
organisms become adapted to their
environment. He explained that
adaptations, like the long necks of
giraffes, as being acquired within the
individuals life time. EX: giraffes
stretched their necks reaching for
leaves on higher branches. Their
offspring had long necks because their
parents stretched.
19th Century Darwin & Modern
Scientists: Because of competition for
leaves, within the giraffe population,
those with longer necks are more likely
to survive and reproduce, thus the gene
frequency for longer necks increases
over generations.