Download Natural Selection and Evidence to Support Evolution

Natural Selection and Evidence
to Support Evolution
1A1: Natural Selection is a major mechanisms of evolution
(Bozeman 001 Natural Selection)
1A2: Natural selection acts on phenotypic variations in
populations
(Bozeman 002 Examples of Natural Selection)
1A4: Biological evolution is supported by scientific evidence
from many disciplines, including mathematics
(Bozeman 004 Evidence for Evolution)
3C1: Changes in genotype can result in changes in phenotype
(Bozeman 033 Genotype & Phenotypes)
Natural Selection is a major
mechanisms of evolution
• This concept is review, remember, natural selection
was the mechanisms proposed by Charles Darwin to
explain how evolution (change over time in
organisms) takes place
• Key ideas of natural selection:
– There is a limited amount of resources
– Differential Survival Rate
– Those better fit for environment produce more offspring
– Over time frequency of favorable trait (allele) increases;
less favorable traits decreases
Genetic Variation
• Recall in order for natural selection to take place
some organisms must be better fit for their
environment than others
• What is the major source of genetic variation?
– MUTATIONS!!! (Or Changes in DNA)
• DNAmRNAprotein
– Proteins make us who and what we are; they are the result of what
we see when we look in the mirror and all the processes that take
place in our body
• A diverse gene pool is important for the survival of
a species; ESPECIALLY in a changing environment
Think Pair Share
• Is there such a think as the “perfect genome”
• Justify your answer
What impact does mutation have on
genotype and phenotype?
• Recall genotype = actual genes; phenotype =
physical characteristics
• Mutations change the DNA (genotype);
however a change in the DNA may or may not
cause a change in the phenotype.
• If the mutation does cause a change in the
phenotype the resulting characteristic can be
negative, positive, or neutral
Think pair share
• What determines the fitness of
a genotype?
• What is fitness?
Phenotype Fitness
• The interaction between the environment and
the phenotype determines fitness
• Fitness – the number of offspring an
organisms produces (genes passed along to
future generations)
• Can the environment act on the genotype?
Justify your answer
Alternative Mechanisms of Evolution
• Natural Selection is the main mechanisms;
however, there are other events that take
place resulting in changes in organism’s
physiology:
– Genetic drift
– Sexual selection
– Artificial selection
Genetic Drift
• Genetic drift: a random event that causes a
change in a populations phenotype
• Two Main Types:
– Bottleneck Effect: a sudden decrease in population
size due to a disaster/war/disease
– Founders Effect: when a small population is separated
from a larger population and creates a new
population
• Genetic Drift has a significant effect on small
populations
Sexual Selection
• Non-random mating
• Mates select based on desired characteristics
– This does not necessarily result in increased
fitness based on the environment
– Ex: Peacocks – female goes after male with larger
tails – detrimental when trying to get away from
predator
Artificial Selection
• Breeding of animals for a desired
characteristic
– Dogs
• Genetic Engineering – producing products
with desired traits
Hardy-Weinberg Equilibrium
• In 1908 a British mathematician and German
physician independently derived an equation to
help determine if a population is evolving
– A population is said to be in Hardy-Weinberg
Equilibrium if:
1.
2.
3.
4.
The population is large
There is no migration (emigration or immigration)
No new mutations
Random mating/no artificial selection
– These conditions are rarely met which is why
populations are constantly evolving
Hardy-Weinberg Equation
• p2 +2pq + q2 = 1
– Expected frequency of the homozygous dominant genotype
+ expected frequency of the heterozygous genotype +
expected frequency of the homozygous recessive genotype
=1
– AA + Aa + aa = 1
• p represents the dominant allele (remember an allele
is only one letter)
• q represents the recessive allele
• p2, 2pq, and q2 all refer to individual organisms
because organisms are diploid (contain two alleles)
• We will play with this equation more next week!!!
Natural Selection acts on phenotypic
variations in populations
• Recall the difference between genotype (actual
genes) and phenotype (physical trait)
• A mutation results in a change in the genotype
• Natural selection can only act (select for or against)
a physical trait
• An environmental change may occur causing a
once detrimental (harmful/bad) trait to become
beneficial (good/useful)
– Historical Example: Peppered moths during industrial
revolution
Phenotypic Variations are not directed
by the environment
• A change in the environment does not cause an
automatic change in population
• Due to variation that already exist in a population
a change in the environment is going to cause the
more beneficial trait to become more dominant
• Changes in physical appearance (phenotype)
occur when there is a change in the genotype
(mutation) and the environment selects for the
phenotype.
Human Impact on Variation
• Artificial Selection: the process by which humans
select for a specific trait they desire in an organism
and sexual reproduce those organisms to produce
offspring with a desired trait (ex: breeds of
dogs/cats/ desired foods)
• Many human behaviors decrease the genetic
variation of organisms – when variation is loss a
population/ecosystem becomes less stable
– What types human behaviors decrease diversity?
– Why does an ecosystem/population become less stable
when variation is lost?
Biological evolution is supported by
scientific evidence
• Information from geographical, geological,
physical, chemical and mathematical
applications are used to understand evolution
• Morphological (how an organisms looks –
phenotype) and genetic (genotype) info of
existing and extinct organisms add to our
understanding of evolution
Fossil Dating
• Age of rocks where a fossil is found
• Rate of decay of isotopes
– Carbon-14
Morphological homologies vs. Vestigial
structures
• Vestigial structures are remnants of functional
structures (used to compare structures and
provide evidence for evolution)
• Morphological homologies represent features
that are shared by common ancestry
Genetic Similarities
• DA nucleotide
• Protein sequences
• Provides evidence for evolutionary ancestry
Evolutionary Models
• Used to illustrate and support evolutionary
concepts:
– Graphical analysis of allele frequencies in a
population (Hardy-Weinberg)
– Analysis of DNA sequences
– Analysis of phylogenetic trees
Changes in genotype can result in
changes in phenotype
• Alterations in a DNA sequence can lead to
changes in the type or amount of the protein
produced and the consequent phenotype
• DNA mutations can be positive, negative, or
neutral based on the effect or the lack of
effect they have on the resulting nucleic acid
or protein and the phenotypes that are
confeered by the protein
Causes of mutations
• Errors in DNA replication
• Radiation and reactive chemicals
• Errors in mitosis or meiosis can result in
changes in phenotype
– Changes in chromosome numbers often result in
new phenotypes