I. What is Evolution? Evolution is the change in the gene pool over time.
A. What is the Gene Pool.
1. It is all the various genes in a species
B. What is a gene?
1. A gene is the sequence of bases on DNA that code for a protein
2. What is DNA?
a. Deoxyribonucleic acid consists of:
·deoxyribose (a sugar with one oxygen)
- purines: adenine and guanine
- pyrimidines: thymine and cytosine
b. The three molecules that constitute DNA are called nucleotides and because
nucleotides repeat themselves throughout the DNA molecule, DNA is called a
c. The DNA molecule consists of two strands of the repeating deoxyribose,
phosphate, and base sequence. The bases in one strand match with predicatable
bases on the opposite strand of the repeating nucleotides (adenine, thymine and
d. Two double-stranded DNA molecules combine to form a chromosome.
C. What is a Chromosome?
1. Chromosomes comprise two DNA molecules (two double-stranded helixes).
2. Each chromosome contains many genes.
3. Different species have different number of chromosomes. The human female has
23 homologous pairs of chromosomes, whereas the human male has 22 homologous
chromosomes and 1 nonhomologous chromosome.
D. What is a Gene?
1. A gene is a sequence of bases on DNA that code for a specific protein. Genes
specify proteins and proteins determine everything else.
2. Genes determine
a. Physical traits, e.g., height, body build, and hair color
b. Metabolic traits, e.g., allergies and ability to process alcohol
c. Growth and Development, e.g., onset of puberty and menopause
E. If genes are found on the DNA, and humans all have the same kind of genes, then why
don't we all look identical?
1. Alleles: are the different forms in which a gene can be found. The different forms
of an allele are slightly different base sequences for the gene. Each human has, except
for men on their one nonhomologous chromosome, two alleles for each gene; one
allele comes from each parent.
a. Blood Type: There are three alleles that code for different sugars or no sugar.
An individual can be aa, ao (type A blood), bb, bo (type B blood), ab (type AB
blood), or oo (type O blood). [The o allele is recessive; it does not code for a
F. How are New Alleles Created?
a. Spontaneous - no known reason
b. Ultraviolet radiation
d. Some chemicals, e.g., chromium, nitrosamines, acetylaminofluorene
ethylnitrosourea, diethyl sulfate
2. The process is random and can occur anywhere along the chromosome or on any
G. The gene pool is all the different alleles of each gene and all the genes that exist in a
H. This means that evolution is the change in the types of alleles of a gene over time,
which expands the gene pool.
1. Although the creation of new alleles is a random process, evolution is not a random
2. Evolution is a result of environmental factors.
Fig. 5.2 In each generation, the shortest-legged pups are selected as parents of the next generation. The lines represent the variation in leg length for a generation. As this process is repeated, the desired feature is gradually developed.
Fig. 5.4A The five categories listed at the left are the basic essentials for the continuation of every species. Each feature of every species can be seen in terms of an adaptation that enables the species to meet its need in one or more of these categories.
Fig. 5.4B In each case, a multitude of features will accomplish the same function. Thus, a tremendous diversity of species exists, each adapted in its own special way.
Fig. 5.5 Specific proteins determine and control physical structure, metabolism and other hereditary attributes of the organism. The DNA molecule is constructed so that it can be chemically replicated, and the coded information may be passed on.
Fig. 5.6A The gene for eye color has two common alleles: one for brown eyes, and one for blue eyes. Matings with different combinations of these alleles are shown.
Fig. 5.6B The gene for eye color has two common alleles: one for brown eyes, and one for blue eyes. Matings with different combinations of these alleles are shown.
II. What is the Evidence Supporting the Theory of Evolution?
3. Over 500 fruitfly species in Hawaii developed from two species
4. Darwin's Finches
C. Fossil Record
D. DNA Record
Fig. 5.7 Selective pressure shows the process of natural selection favoring giraffes with longer necks.
Fig. 5.9 population spread over a broad area may face selective pressures. If the population splits so that interbreeding among the subpopulations does not occur, the different selective pressures may result in the subpopulations evolving into new species.
Fig. 5.11 The similarities among these birds attest to their common ancestor. Selective pressures to feed on different foods have caused modification and speciation in adapting subpopulations.
III. Evolution is a Response to Environmental Change (or the absence of a species in a particular niche)
A. The movement of planet's plates (Theory of Plate Tectonics) is an example of substantial environmental change that produced a wide array of species occupying
similar niches and habitats.
B. Species respond to environmental change in different ways.
1. Adaptation (by evolution) for:
a. coping with abiotic factors - polar bear's heavy fur, leaf drop in summer by
b. obtaining food - a frog's tongue, broad plant leaves, different mouth parts of
c. escaping predation - thorns on plants, warning colors on insects, carapace of
d. pollination - flower color, quantity of pollen or nectar, insect mouth parts
e. finding/attracting mates - deer antlers, peacock tails, bright colors of male
f. seed dispersal - wings, hooks
a. A species will migrate if it can. The new environmental conditions must be
C. What determines if a species will be able to survive change?
1. Rate and degree of environmental change
2. The genetic variability within the species
3. Biotic potential
4. Size of organism
5. Specialization to a given habitat and/or food supply (generalists versus specialists)
6. Geographic distribution
Fig. 5.16 This is a summary of factors affecting the survival of species when the environment changes.
Fig. 5.17 This figure shows the 14 major tectonic plates making up Earth's crust. The arrows in the figure indicate 20 million years of movement.
Fig. 5.18A Similarities of rock types, the distribution of fossil species, and other lines of evidence indicate that 225 million years ago all the present continents were formed into one huge land mass that we now call Pangaea.
Fig. 5.18B Slow but steady movement of the tectonic plates over the intervening time caused the breakup of Pangaea and brought the continents to their present positions.
Fig. 5.21A Contrasting the geological time scale with a single year gives an appreciation for the relative amount of time taken for various evolutionary stages. Note that two-thirds of the time is taken in the development of cells; then the pace quickens. The first vertebrates do not appear until November 22.
Fig. 5.21B Contrasting the geological time scale with a single year gives an appreciation for the relative amount of time taken for various evolutionary stages. Note that two-thirds of the time is taken in the development of cells; then the pace quickens. Humans arrived in the last 8 hours.