Transcript The Genetic Basis of Development

Biotechnology applications
• If I was taking the AP test, I would be sure
to know about…
– Stem Cells: and the controversy
– Application of biotech such as
•
•
•
•
•
416-423
Diagnosis of disease
Gene therapy
Development of drugs
Forensics and paternity
– Short tandem repeats (STRs)
• Environmental clean-up
• Genetically modified organisms.
Charles Darwin
Pre-Darwin
Lyell: Geology, Uniformitarianism very old
earth.
Malthus: Exponential Population Growth
LaMarck: Evolution. Inheritance of acquired
characteristics (wrong, but still evolutionary)
The Voyage of the
HMS Beagle
Natural Selection
Observation 1: Variation
No two organisms are
completely alike.
Observation 2: Reproduction…
…And overproduction
Inference 1: Differential “fitness” in the
environment due to variations.
The “struggle for existence”
Inference 2: Over the span of geological
time (billions of years), inheritance of
adaptations will lead to evolution of the
population.
Fundamental Conclusions
1. To develop the diversity of life seen on
the Earth today, the Earth has to be
incredibly old.
2. If organisms evolve from pre-existing
organisms, then all organisms should
share a universal “common ancestor”
“tree thinking”
Unsettled by Darwin
1. Origin of Life
1. Origin of species
1. Nature of variation/inheritance
1.1: Natural selection is a major mechanism of evolution
2. THE MODERN SYNTHESIS
The “Modern Synthesis”
Connects Darwinian evolution to genetics
and modern understanding of inheritance.
Where Traits come from:
Trait
Variation comes from Mutation
Mutation: A change in a DNA sequence.
Happens spontaneously and unavoidably.
Mutations create “alleles”
Alleles: Different versions of the genes for
a trait.
Evolution Defined:
Evolution: Changes in allele frequencies
over time.
Ex. Galapagos Finches
Grant and Grant: Studied the finch
population on an isolated island in the
Galapagos.
Measured the beak dimensions of all
birds on the island every year for
decades.
Connected changes in beak dimensions to
fluctuations in the environment
(precipitation, seed sizes)
Evolution Misconception Alert!
Misconception: Individuals evolve.
Evolution is a “population level” phenomenon.
Individuals DO NOT evolve!
The evolution of a population emerges from the
individual fitness of members of that population.
As they survive and reproduce or not, the
frequencies of alleles in the next generation will
change accordingly.
Pg. 468-475
• Watch Bozeman science on Hardy
Weinberg calculations
Evolution
• Changes in the genetic makeup of
populations overtime
• Changes in the genetic makeup lead to
changes in phenotypes- variation
• Favorable variations for a particular
environment are known as adaptations
Microevolution and Macroevolution
• Microevolution refers to the changes in the
genetic makeup over time
• Macroevolution refers to the origin and
extinction of species and that fuel the
diversification of life
• Populations evolve, individuals do not
• Population- a group of individuals of a
single species that live and interbreed in a
particular geographic area at the same
time
Gene Pools and Gene Frequencies
• Gene Pool- the sum of all the alleles in a
population; the sum of the genetic
variation within a population
• Allele Frequency- the proportion of each
allele in the gene pool
• Genotype Frequency- the proportion of
each genotype (homozygous dominant,
heterozygous, homozygous recessive) in a
population
Hardy-Weinberg Theorem
• Describes the gene pool of an idealized, nonevolving population to which others may be
compared
• States that the frequency of alleles and genotypes
in a population’s gene pool remains constant from
generation to generation provided that only
Mendelian segregation and recombination of
alleles are at work
Evolution vs. Genetic Equilibrium
To understand how populations
evolve over time, scientists find it
helpful to determine what
happens when no change takes
place…
Genetic Equilibrium
Hardy-Weinberg principle:
Allele frequencies in a population will remain constant
unless one or more factors cause those frequencies to
change.
5 conditions are required to maintain genetic
equilibrium…
If conditions are not met, the population will evolve.
REVIEW!!!
What is genetic drift?
A population’s gene pool has
to be kept together and
separate from the gene
pools of other
populations
No selective pressures!!
Conditions of Hardy-Weinberg
Equilibrium
1. The population size is extremely large
2. There is no gene flow occurring (no
movement of individuals into or out of the
population)
3. There is no mutation
4. Random mating occurs
5. There is no natural selection acting on the
population
• Any departure from the five conditions usually results in
evolution
Two major uses for scientists
• Useful for predicting the approximate
genotype frequencies of a population from
its allele frequencies
• Allows biologists to evaluate which
mechanisms are acting on the evolution of
a particular population
Hardy-Weinberg Equilibrium
p2 + 2pq + q2 = 1
• p represents the frequency of one allele (usually dominant)
• q represents the frequency of the other allele (usually
recessive)
• p2 represents the frequency one homozygous genotype
(usually homozygous dominant)
• q2 represents the frequency other homozygous genotype
(usually homozygous recessive)
• 2pq represents the frequency of the heterozygous genotype
• Frequencies are usually given as percentages, but
should be converted to decimals to work the
problems; move the decimal 2 places to the left
• The frequency of p and q must also equal 1: p + q
=1
Solving Hardy-Weinberg Problems
• Examine the question to determine what piece of
information you have been given about the
population. In most cases, you will be given the
percentage or frequency of the homozygous
recessive phenotype or homozygous dominant
phenotype
– Remember that genotype and phenotype are not the
same
• The recessive phenotype represents the genotype
q2 always
• The dominant phenotype represents the
combination of the p2 genotype and the 2pq
genotype
• The first objective is to find out the value of p or q. If
this is achieved, then every other value in the equation
can be determined by simple calculation.
• Take the square root of q2 to find q
• Determine p by subtracting q from 1
• Determine p2 by multiplying p by itself
• Determine 2pq by multiplying p times q times 2
• Check that your calculations are correct by adding up
the values for p2 + 2pq + q2 (the sum should equal 1 or
100%)
Example Problem: In the Caucasian American population
approximately 70% of people can taste the chemical
phenylthiocarbamide (PTC), the dominant phenotype, while 30%
are non-tasters, the recessive phenotype. Determine the
frequency of :
The homozygous recessive phenotype (q2):
The dominant allele (p):
Homozygous tasters (p2):
Heterozygous tasters(2pq):
Darwin’s Observations
• Resources are limited
• Organisms will fight or struggle for resources
• Variation in organisms leads to differential
success
• Those organisms that are able to survive and
reproduce will pass their characteristics on to
the next generation
Defining “Survival of the Fittest”
• Fitness refers to the best adapted individuals
for a particular environment
• Survival refers to the ability to not only live,
but reproduce, thus passing on adaptive traits
to the next generation
• LINK IT TO GENES!!!
– Favorable phenotypes don’t just appear
– Favorable mutations to genes result in adaptive
phenotypes
Darwin’s Ideas
• On The Origin of Species By Means of Natural Selection
• Major points of Darwin’s Theory:
– Species are not constant, they change over time (evolve)
– All species share a common ancestor
– The mechanism that produces changes in a species is
natural selection
•
• Natural Selection: The differential survival and
reproduction of individuals in a population based on
variations in their phenotypes