Transcript Population - Madeira City Schools

I. Theory of Evolution
A. Overview
1. "Theory vs. Scientific Theory"
a. "Theory" in everyday language is a guess
b. "Scientific Theory" is supported by a large amount
of evidence. An explanation of observations.
2. Definition of Evolution -- Change in a population over
time
a. The smallest unit that can change is a population.
b. An organism does not evolve, a population does.
B. Lamarck: French naturalist, published his hypothesis in
1809.
1. Who was he? (a few fun facts)
a. Frenchman
b. [1744-1829]
c. Soldier in the French army…injury
made him leave
d. Botanist who lived in poverty
e. Appointed professor of natural history of insects and
worms (knew nothing about these things)
f. Coined the term “invertebrate”
2. Lamarck’s Theory is based on his observations
a. He observed that blacksmiths had big muscles and
that family members stayed in the profession.
b. organisms constantly strive to improve self and
become more advanced.
c. effort to improve causes the most used body
structures to develop while the unused body
structures wasted away (Use Disuse theory)
d. the modification due to use or disuse is passed on to
offspring (Inheritance of Acquired Characteristics)
e. Another example he used is giraffes necks
3. Weismann (1889): Proves Lamarck wrong
a. cut off the tails of mice for 22 generations.
b. All offspring were born with tails.
c. He concluded that changes in the body during your
life are not passed down to offspring. (we know this
now through genetics)
C. Charles Darwin
1. growing up years
2. education
3. Voyage of the Beagle (1831-1836)
a. purpose of the voyage was to make maps of coast of
South America
b. Darwin’s purpose was to make geological studies to
locate minerals for mining…he was also the ships
naturalist.
c. Darwin observed plants and animals every time they
docked.
d. He noticed slight differences in them based on where
they were
e. He collected fossils and made notes about where he
found them.
4. Visit to the Galapagos
Islands during his voyage
a. Local Finches (a type of
bird) had different types of
beaks based on what they ate
b. Tortoises had different
shells based on what island
they were on
c. Why were they different?
How did they get that way?
5. Darwin’s Theory was influenced by 3 people
a. Charles Lyell – wrote a book explaining that changes in
the Earth were slow and uniform
Darwin – slow Earth changes could affect plants and
animals
b. Thomas Malthus – observed that the human population
was growing so fast that the supply of resources would
not be able to support the population
Darwin – There was always competition for food,
space, and mates. Those that “win”
survive and reproduce.
c. Pigeon and Dog Breeders – select animals with the best
traits to get the desired pigeon or dog
Darwin – thought this process would naturally
occur, but slower.
6. Darwin’s Theory of how evolution has occurred:
Natural Selection
a. There is a variety within a population
b. Some traits are an advantage to have (they improve the
organisms chance to reproduce)
c. More young are created than the environment can
support
d. Those that survive and reproduce are those with the
traits that are an advantage to have
e. Over a long time, small changes accumulate and the
population changes.
7. Darwin did not publish his theory for more than 20 years.
He published On the Origin of Species in 1859.
II. Evidence of Evolution
A. Study of fossils provides strong evidence for evolution
1. Paleontologist
2. Fossil Record – the sequence in which fossils appear within
layers of sedimentary rocks
a. sedimentary rocks form from layers of sand and mud that
settle to the bottom of seas, lakes and swamps.
b. rock forms strata – layers of sedimentation. Younger ones
are on top, older at the bottom.
3. relative dating of fossils = how old fossils are in relation to
one another (younger fossils are located on top of older fossils)
4. absolute dating of fossils = exact age of fossils using
radioactive elements
a. Half-life = amount of time required for one-half of a sample
of radioactive mineral to change into another
substance
B. Biogeography = geographical distribution of species
1. Darwin saw that organisms on islands with similar
environments in different parts of the world, resemble
organisms on the mainland close to them instead of
organisms on the island
a. Continental island = island that at one time was attached to
the mainland
b. Volcanic island = island made from volcanic eruptions
(Hawaii and Galapagos Islands)
fewer species than continental
no native mammals except bats
no amphibians
large portion of species are endemic = occur
nowhere else in the world
C. Comparative Anatomy
1. Homologous structures = similarity in structure because they
evolved from a common ancestor (functions may be different)
2. Analogous structures = similarity in function, but a different
structure.
a. wings of insects and wings of birds
b. used as evidence to show evolution of ancestors adapting to
similar environmental conditions = convergent evolution
3. Vestigial structures = structures of marginal, if any, importance.
a. historical remnants of structures that were important in
ancestors
b. represent changes in an organism’s embryonic development
brought about by natural selection
Homologous Structures
D. Comparative Embryology
1. Ontogeny = development of an individual
2. Phylogeny = evolutionary history of a species
3. “Ontogeny recapitulates phylogeny” = development of an
individual is a replay of its evolutionary history
a. similarities in embryonic development suggests evolution
from a common ancestor
b. in order to develop certain structures in the womb, they
have to have the genes to do so
4. All vertebrate embryos have gill pouches and gill arches, and
fish-like circulatory system (therefore they must have
similar genes to develop these)
Human embryo
Chick embryo
E. Molecular Biology
1. Similarities in Proteins
a. Degree of similarity among amino acid sequence
corresponds to relatedness
b. Evolutionary relationships between humans and 5 other
vertebrates based on hemoglobin comparisons shown in chart
below.
2. Similarities in rRNA
3. Similarities in
noncoding sequences
a. thought of as “fossil
DNA”
III. The evolution of populations
A. Populations are the units of evolution (not an individual
organism)
1. Population – group of individuals of the same species living in
the same place at the same time that can interbreed and
produce viable offspring.
2. Biologists focus on the gene pool = total collection of genes in
a population at any one time.
a. all alleles in all the individuals making up a population
b. Microevolution = when the relative frequencies of alleles
in a population change over a number of generations
B. How does a population get genetic variation?
1. Crossing over
2. Independent assortment
3. Sexual reproduction
4. Mutation
C. How do you know if a population is evolving?
1. Hardy-Weinberg Theorem – developed in 1908
a. Mathematical model to show change in gene frequencies
within a population, over time.
b. Used to calculate the frequencies of possible genotypes
future generations.
basic equation:
p+q=1
p = % dominant allele
q = % recessive allele
expanded equation: (p + q)2 = (1)2
p2 + 2pq + q2 = 1
genotypes
p2 = homozygous dominant
2pq = heterozygous
q2 = homozygous recessive
in
2. If a population is not evolving, then the frequencies of genes
and genotypes will remain the same through the generations
a. the population is at “equilibrium”
3. In order for equilibrium to be possible, the following 5 things
must occur.
a. the population is extremely large
b. it must be isolated from other populations
c. no net mutations occur
d. random mating must occur (no sexual selection)
e. no natural selection occurs
4. The HW equation is used as a baseline--if frequencies deviate
from HW values, then the population is evolving
a. population still evolves even if at one gene loci
5. Microevolution is caused by violations of the 5 HW
assumptions.
You have sampled a population in which you know that the percentage
of the homozygous recessive genotype (aa) is 36%. Using that 36%,
calculate the following:
A. the frequency of the “aa” genotype
B. The frequency of the “a” allele
C. The frequency of the “A” allele
D. The frequencies of the genotypes “AA” and “Aa”
E. The frequencies of the two possible phenotypes if “A” is
completely dominant over “a”.
There are 100 students in a class. Ninety-six did well in the course
whereas four blew it and received a grade of F. Sorry. In the highly
unlikely event that these traits are genetic rather than environmental, if
these traits involve dominant and recessive alleles, and if the four (4%)
represent the frequency of the homozygous recessive condition, please
calculate the following:
A. The frequency of the recessive allele
B. The frequency of the dominant allele
C. The frequency of the heterozygous individuals.
D. Mechanisms of Microevolution
1. Genetic drift = change in gene pool of a small population due to
chance.
a. Bottleneck effect = genetic drift resulting from an event
that drastically reduces population size
b. Founder effect = random change in the gene pool that occurs
in a small colony of a population
Example: “Founding population” of an island
2. Gene flow = gain or loss of alleles from a population by
the movement of individuals or gametes
a. migration of individuals into (immigration) or out of
(emigration) an area.
b. plant pollen
3. Mutation = random change in an organism’s DNA that creates
a new allele
a. raw material for evolution
4. Nonrandom mating = selecting mates (“sexual selection”)
rather than by chance
5. Natural Selection = differential success in reproduction
E. Natural Selection can alter variation in a population in 3 ways
1. Stabilizing selection favors intermediate phenotypes.
2. Directional selection shifts the overall makeup of the
population by acting against individuals at one of the
phenotypic extremes.
3. Disruptive selection occurs when environmental conditions
are varied in a way that favors individuals at both extremes of
a phenotypic range.