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BIO SCI 94 Study Guide - Midterm Guide: Allele Frequency, Genetic Drift, Frequency-Dependent Selection


Department
Biological Sciences
Course Code
BIO SCI 94
Professor
Catherine Loudon
Study Guide
Midterm

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Bio 94 Midterm #1 Review
Chapter 1: Introduction
Pgs. 5 – 14
Evolution- is a change in the characteristics of a population over time. It means that
species are not independent and unchanging entities, but are related to one another and
can change through time.
Natural Selection- Darwin and Wallace developed. Explains how evolution occurs.
Two conditions of Natural Selection:
1. Individuals within a population vary in characteristics that are heritable
(population defined as a group of individuals of the same species living in the
same area at the same time)
2. Certain versions of these heritable traits help individuals survive better or
reproduce more than do other versions.
Natural selection acts on individuals, but evolutionary change occurs in populations.
Artificial selection- changes in populations that occur when humans select certain
individuals to produce the most offspring
Fitness- the ability of an individual to produce viable offspring. High fitness= more
surviving offspring
Adaptation- a trait that increases the fitness of an individual in a particular environment
Cell theory and the theory of evolution:
1. The cell is the fundamental structural unit in all organisms.
2. All species are relate by common ancestry and have changed over time in
response to natural selection
Speciation- One species diverge and form new species
Taxonomy- the effort to name and classify organisms
Domain- a taxonomic category that contains Bacteria, Archaea, and Eukarya
Phylum- refer to major lineages within each domain
Genus- first part of name; is made up of a closely related group of species
Species- second part of name, identifies the organism’s species
Null hypothesis- specifies what should be observed when the hypothesis being tested
isn’t correct
Important Characteristics of a Good Experimental Design
1. It is critical to include control groups
2. The experimental conditions must be as constant or equivalent as possible
3. Repeating the test is essential
Overall summary:
- The theory of evolution states that all organism are related by common ancestry
- Natural selection is a well-tested explanation for why species change through time
and why they are so well adapted to their habitats
- The theory of evolution predicts that all organisms are part of a genealogy of
species, and that all species trace their ancestry back to a single common ancestor
- To construct this phylogeny, biologists have analyzed the sequences in rRNA and
in an array of genetic material found in all cells
- A tree of life, based on similarities and differences in these molecules, has three
fundamental lineages, or domains: the Bacteria, the Archaea, and the Eukarya
- Biology is a hypothesis-driven, experimental science

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Chapter 25: Evolution by Natural Selection pgs. 446-454, 456-462
Predictions about the nature of species:
1. Species change through time
2. Species are related by common ancestry
Extant species- species living today
Earth is about 4.6 billion years old, and the earliest signs of life appear I rocks that
formed 3.4-3.8 billion years ago.
Recent analyses of the fossil record suggest that over 99 percent of all the species that
have ever lived are now extinct
Transitional feature- a trait in a fossil species that is intermediate between those of
ancestral (older) and derived (younger) species
Vestigial trait- a reduced or incompletely developed structure that has no function, or
reduce function, but is clearly similar to functioning organs or structures in closely
related species
Homology- similarity that exists in species because they inherited the trait from a
common ancestor (ex. Human hair and dog fur)
1. Genetic homology- occurs in DNA nucleotide sequences, RNA nucleotide
sequences, or amino acid sequences
2. Developmental homology- recognized in embryos. Ex. Early chick, human,
and cat embryos have tails and gill pouches
3. Structural homology- similarity in adult morphology or form ex. Limbs of
vertebrates
*The three levels of homology interact. Genetic homologies developmental
homologies structural homologies
Darwin’s Four Postulates
1. Individual organisms that make up a population vary in the traits they possess,
such as size and shape
2. Some trait differences are heritable
3. In each generation, many more offspring are produced than can possibly
survive. Only some individuals in the population survive long enough to
produce offspring
4. Individuals with certain heritable traits are more likely to survive and
reproduce. Natural selection occurs when individuals with certain
characteristics produce more offspring than do individuals w/o those
characteristics
*Evolution by natural selection occurs when 1) heritable variation leads to 2) differential
reproductive success
Some misconceptions regarding natural selection and adaptation
Natural selection just sorts existing variants-it does not change them
Acclimization- a change in an individual’s phenotype that occurs in response to a change
in natural environmental conditions are NOT passed on to offspring because no alleles
have changed
Adaptations occur because organisms want or need them
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CORRECTION: Mutation the source of new alleles occurs by chance, evolution
is not goal directed or progressive, there is no such thing as a higher or lower
organism
Organisms sacrifice themselves for the good of the species
CORRECTION: Individuals with alleles that cause self-sacrificing behavior die
and do not produce offspring, so alleles are eliminated from the population
Evolution perfects organisms
CORRECTION: Some traits are nonadaptive, cannot be optimized due to fitness
trade-offs, limited by genetic or historical constraints
Fitness trade-off- a compromise between traits in terms of how those traits perform in
the environment. Because selection acts on many traits at once, every adaptation is a
compromise
Chapter 26: Evolutionary Processes
Pgs. 465-472
Hardy-Weinberg principle- serves as a mathematical null hypothesis for the study of
evolutionary processes. The two fundamental claims of this principle is:
1. If the frequencies of alleles A1 and A2 in a population are given by p and q,
then the frequencies of genotypes A1A1, A1A2, and A2A2 will be given by
p^2, 2pq, and q^2
Allele frequencies p+q=1
Genotype frequencies p^2+ 2pq+ q^2=1
2. When alleles are transmitted via meiosis and random combinations of
gametes, their frequencies do not change over time. For evolution to occur,
some other factor or factors must come into play.
5 assumptions that HW principle makes:
1. Random mating
2. No natural selection
3. No genetic drift (random allele frequency changes)
4. No gene flow- No new alleles were added by immigration or lose through
emigration
5. No mutation
Inbreeding- the mating between relatives
1. Inbreeding increases homozygosity
2. Inbreeding itself does not cause evolution because allele frequencies do not
change in the population as a whole
3. Nonrandom mating changes only genotype frequencies, not allele frequencies
* Inbreeding can speed the rate of evolutionary change. It increases the rate at which
natural selection eliminates recessive deleterious alleles that lower fitness
Inbreeding depression- the decline in average fitness that takes place when
homozygosity increases and heterozygosity decreases in a population
1. Many recessive alleles represent loss-of-function mutations
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