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Genetics and Evolution


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Title: Genetics and Evolution

Chapter 2
  • Genetics and Evolution

Chapter Preview
  • What Is Evolution?
  • What Is the Molecular Basis for Evolution?
  • What Are the Forces Responsible for Evolution?

Creation vs. Evolution
  • All cultures have stories and myths about the
    creation of the world and human beings
  • Evolution differs from these creation stories by
    offering consistent and testable explanation for
    the origins and diversity of life

The Classification of Living Things before the
  • Great Chain of Being a classification system
    developed by Aristotle that grouped living and
    non-living things into groups based on
  • Each group had a primate or best example for
    the group.
  • The groups were organized in a hierarchy, from
    inferior to superior.

The Great Chain of Being An Example
  • God
  • Angels
  • Humans
  • Birds
  • Terrestrial Animals
  • Plants
  • Rocks

The Classification of Living Things after the
  • Linnaean Classification a classification
    system developed Carl Von Linné that grouped
    living things into groups based on similarity of
    form, function, and growth.
  • Placed humans among the primates (also including
    apes, monkeys, and prosimians) and mammals
    (animals having fur or hair and who suckle their

The Classification of Living Things after the
  • Linnaeuss system relied on a Binomial
    Nomenclature which organized living things into
    species (reproductively isolated populations) and
    genera (singular genus), a more inclusive
    grouping of similar organisms
  • Examples of genus/species
  • humans Homo sapiens
  • chimpanzees Pan troglodytes
  • lowland gorillas Gorilla gorilla
  • saber-toothed tigers Smiladon fatalis

The Classification of Living Things after the
  • Like Linnaeus, modern Taxonomy uses body
    structure, body function and patterns of growth
    but also examines genetic material and protein
    structures to make classifications

The Classification of Living Things after the
  • Modern Cladistics compares animals based on
  • Analogies anatomical features with similar
  • Homologies anatomical features evolved from a
    common ancestral form

Visual Counterpoint Class
  • Using cladistics, are the wings of birds and
    butterflies analogies or homologies?

Visual Counterpoint Class
  • Using cladistics, are the wings of bats and hands
    of humans analogies or homologies?

Visual Counterpoint Class
  • Are the anatomical features of the following
    organisms analogies or homologies?
  • 1. dolphin and shark morphology
  • 2. bat and bird wings
  • 3. primate opposable thumbs and panda thumbs
  • 4. seal flippers and human hands

The Discovery of Evolution
  • At first, the fossilized remains of animals found
    in Europe were interpreted according to religious
  • These interpretations relied on several
  • Fixity of Species (species were created only once
    and did not change over time)
  • The Great Chain of Being

The Discovery of Evolution
  • Early interpretations, relying on the notion of
    fixity of species, argued that fossil animals had
    become extinct.
  • For example, George Cuvier invoked catastropes
    like the Great Flood of the Book of Genesis to
    explain the existence of extinct animals such as
    mammoths (catastrophism)

The Discovery of Evolution
  • Jean-Baptiste Lamarck, was among the first to
    suggest an evolutionary mechanism to account
    for the diversity of living creatures
  • His theory of the inheritance of acquired traits
    proposed that intentional behavior on the part of
    individuals brought about changes in the form of
    entire species

The Discovery of Evolution
  • An Example of Lamarcks Theory
  • The first giraffe gained its long neck by
    stretching to reach the leaves on the highest
    tree top branches and in turn passed this
    acquired long neck onto its offspring.

The Discovery of Evolution
  • Sir Charles Lyell developed the idea of
  • Argued that the major features on earths surface
    (ex mountains and canyons) through the gradual
    accumulation of minute changes, brought about by
    the same natural processes, such as erosion, that
    are observable today.

The Discovery of Evolution
  • A Major Consequence of Uniformitarianism
  • The time depth required for these changes was
    not compatible with literal interpretations of
    the Bible in which the earth is said to be six
    thousand or so years old

The Discovery of Evolution
  • Darwins Precursors
  • Lamarcks theory of evolution recognized that
    species did change (but was wrong about how)
  • Lyells uniformitarianism expanded the age of the
    earth (allowing more time for evolution to
  • 3. Malthus observed that animals produce many
    offspring but not all of them live to maturity

The Discovery of Evolution
  • Darwins Theory of Evolution by Natural
  • All species display a range of variation, and all
    have the ability to expand beyond their means of
  • In their struggle for existence, organisms with
    variations that help them to survive in a
    particular environment will reproduce with
    greater success than those without them.
  • As generation succeeds generation, nature selects
    the most advantageous variations, and species

It was assumed that all offspring had a
mixture of parental traits.
Gregor Mendel and The Science of Heredity
  • Experimented with plant pollination to establish
    the laws of heredity
  • Mendel discovered that inheritance was
    particulate, rather than blending as Darwin
  • Ironically, Darwin had his 1866 paper but did not
    read it
  • Mendels work gave rise to science of genetics

Mendel's Law of Segregation
  • During reproduction, the genes governing the
    expression of a trait will be separated and keep
    their individuality
  • They will be passed on to the next generation,
  • Today, we know this is due to meiosis

Mendel's Law of Independent Assortment
  • During reproduction, each parent donates
    segregated genes
  • In the offspring, these segregated genes
    recombine in a random manner and independently
    from one another
  • Thus, individual traits are inherited
  • independently

Heredity and the Molecular Basis for Evolution
Genes (Mendels particles) a section of DNA
which codes for the production of a specific
protein DNA Deoxyribonucleic Acid (limited to
the nucleus of a cell) Chromosomes compacted
and coiled DNA (usually occurs when a cell
divides) Alleles variants of a gene that occur
in the same location on a chromosome or DNA
Humans have 23 pairs of Chromosomes
Humans have 23 pairs of Chromosomes
Humans have 23 pairs of chromosomes or a total of
46. Cells with all 46 (23 pairs) are known as
diploid Cells with only 23 (no pairs) are known
as haploid
The DNA Molecule
DNA looks like two strands of a rope twisted
around each other with ladderlike steps between
the two strands Alternating sugar and phosphate
molecules form the backbone of these strands
connected to each other by four base pairs
adenine (A), thymine (T), guanine (G), and
cytosine (C). Connections occur between
complementary pairs of bases (A to T G to C)
DNA cannot leave the cells nucleus.
Not All DNA Occurs In the Nucleus
  • Mitochondrial DNA (mtDNA) found in the
    mitochondria of animal cells (does not code for
    any physical traits but can be used to examine
    genetic relationships to others in a population).
  • Retroviruses do not have DNA but consist of RNA

Protein Synthesis
  • Groupings of three base pairs (codons) code for
    particular amino acids.
  • A gene is nothing more than a series of codons
    which tell cells which amino acids to make in
    order to produce a protein (this process is known
    as protein synthesis).

Protein Synthesis
  • Because DNA cannot leave the nucleus of a cell,
    the directions for a specific protein are first
    converted into ribonucleic acid or RNA in a
    process called transcription.
  • RNA differs from DNA in the structure of its
    sugar phosphate backbone and in the presence of
    the base uracil (U) rather than thymine (T).

Protein Synthesis
The RNA travels to the ribosomes, the cellular
structure where translation of the directions
found in the codons into proteins occurs.
Mitosis - Cell Division
  • In order to grow, maintain good health, and
    heal, the body cells of an organism must divide
    and produce new cells.
  • Cell division is initiated when the chromosomes
    form a second pair that duplicates the original
    pair of chromosomes in the nucleus.

Mitosis - Cell Division
  • The DNA unzips between the base pairs (adenine
    from thymine and guanine from cytosine)
  • Afterwards, each base on each now-single strand
    attracts its complementary base, reconstituting
    the second half of the double helix.
  • Each new pair is then surrounded by a membrane
    and becomes the nucleus that directs the
    activities of a new cell.

Meiosis Sex Cell Production
  • Sexual reproduction actually increases genetic
    diversity in a species.
  • However, if two regular body cells, each
    containing 23 pairs of chromosomes, were to
    merge, the result would be a new individual with
    46 pairs of chromosomes, followed by individuals
    with up to 92 pairs of chromosomes in the next
    generation and so on. These individuals would
    not live.

Meiosis Sex Cell Production
  • To solve this problem, meiosis begins like
    mitosis, with the replication and doubling of the
    original genes in chromosomes through the
    formation of sister chromatids, but it proceeds
    to divide that number into four new cells rather
    than two.
  • Each resulting sex cell (sperm and ova) has only
    half the number of chromosomes compared to the
    parent cell.

Meiosis Sex Cell Production
Meiosis Sex Cell Production
  • Following Mendels law of segregation, the
    alleles from the parent chromatid are separated.
  • In homozygous individuals with identical alleles,
    the sex cells have the same alleles.
  • In heterozygous individuals with different
    alleles, half the sex cells will one allele, the
    other half will have a different allele for the
    same trait.

Phenotype and Genotype
  • A persons phenotype are the traits that are
    visible or observable.
  • A persons genotype or genetic composition can
    never be fully predicted because of the
    segregation and independent assortment of genes
    and alleles.
  • In addition, during meiosis corresponding
    portions of one chromosome may cross over to
    the other one, somewhat scrambling the genetic
    material compared to the original chromosomes.

Mendel's Law of Dominance
  • Not all of the genes/alleles present in an
    organism (the genotype) will be expressed
    physically (the phenotype).
  • Some genes/alleles are recessive and will not be
    expressed in the presence of dominant genes or
  • In some cases, genes/alleles may be codominant
    with others and both will be expressed

Mendel's Law of Dominance
  • Best Example human blood groups
  • 4 Phenotypes 6 Genotypes
  • A AA, AO
  • B BB, BO
  • AB AB
  • O OO
  • Which alleles for human blood types are dominant,
    codominant, and recessive?

Punnett Squares
  • A method for measuring the probability of a
    certain genotype appearing based on the crossing
    of two organisms with known genotypes. Based on
    Mendels Laws of Segregation and Independent
  • How would it work for human blood types?

Punnett Squares For Class Discussion
  • Try using a simple punnett square for one
    generational cross between people with the
    following Mendelian traits
  • Tongue rollers homozygous for the dominant
    trait (TT) or heterozygous (Tt) non-tongue
    rollers are homozygous for the recessive trait
  • 2. Dwarfism homozygous for the dominant trait
    (DD) non-dwarfs are homozygous for the recessive
    trait (dd) or are heterozygous (Dd)

Polygenetic Traits
  • Mendels laws work best for Mendelian traits
    physical traits coded by one gene (with multiple
  • Most human traits (like height and skin color)
    are polygenetic and are coded on several genes

Evolution, Population, and Individuals
  • Evolution acts on individual traits but
    individuals do not evolve, only populations
    evolve (over an extended period of time)
  • Populations that can still produce fertile
    offspring are still considered part of the same
  • Such populations have a distinctive gene pool or
    all of the genetic variation possessed by
    individuals in the population.

Evolution, Population, and Individuals
  • Over time, changes in the frequency of alleles
    among different populations lead to noticeable
    differences in the phenotypes of the members of
    these populations.
  • Eventually, the genetic and phenotypic
    differences will result in reproductive isolation
    the populations will no longer be able to
  • So how do populations in a species accumulate
    enough genetic and phenotypic differences to be
    considered different species? ANS -

The Hardy-Weinberg Principle
  • Demonstrates that there will be no changes in a
    populations allele frequencies over time, if
  • mating is entirely random
  • the population is sufficiently large for
    statistical averages to express themselves
  • no new variants are introduced into the
    populations gene pool
  • all individuals are equally successful at
    surviving and reproducing
  • However, none of these conditions ever applies
    to populations of living things so allele
    frequencies do change over time!

The Forces of Microevolution
  • Mutation
  • Genetic Drift
  • Gene Flow
  • Natural Selection

  • Random genetic change occurring during mitosis or
  • Can be beneficial, harmful, or not noticeable
  • Mutagens or chemical in the environment can
    increase the chances of mutation
  • Without the variation brought in through random
    mutations, populations cannot change over time in
    response to changing environments

Genetic Drift
  • Chance changes in the allele frequencies of a
    population due to accidents or other events
  • Result in greater changes when populations are
    small or isolated the founder effect

Gene Flow
  • Changes in the allele frequencies of a population
    due to the infusion of genetic material through
    interbreeding with another population
  • Among humans, social factors like mating rules,
    intergroup conflict, and our ability to travel
    great distances can affect gene flow

Natural Selection
  • Natural selection refers to the evolutionary
    process through which genetic variation at the
    population level is shaped to fit local
    environmental conditions.
  • Natural selection ? survival of the fittest in
    the sense meant by Herbert Spencer
  • Best measured through reproductive success
    -mating and production of viable offspring who
    will in turn carry on ones genes

Adaptation and Physical Variation
Evolution often involves balancing the
beneficial and harmful effects of a specific
allele. Such is the case with sickle-cell anemia
Sickle Cell Anemia
A painful disease in which the oxygen-carrying
red blood cells change shape (sickle) and clog
the finest parts of the circulatory system
Originated as a mutation.
Sickle Cell Anemia
Individuals who are homozygous for the sickle
cell trait frequently die at a young
age. Individuals who are homozygous for normal
red blood cells are more susceptible to
malaria. Individuals who are heterozygous for the
sickle cell trait enjoy some protection from
malaria but risk creating a homozygous offspring.
Sickle Cell Anemia and Malarial Environments