Week 7
DNA Chapter 13
Nucleus contains DNA.
DNA is composed of molecular subunits called nucleotides. Each nucleotide
consists of 3 parts
1. a five carbon sugar, deoxyribose
2. a phosphate group
3. a nitrogen containing organic compound called a base.
There are four bases: cytosine (C), thymine (T) are called pyrimidine bases,
Adenine (A) and guanine (G) are called purine base
Consider these four bases as an alphabet, the sequence in which they occur
determines the genetic message…
Double helix discovered by Watson and Crick…2 strands.
Adenine (A) always pairs with thymine (T) and guanine (G) always pairs with
acytosine (C), so that by knowing one sequence you will always be able to know
its corresponding sequence.
In the Synaptic Phase of Interphase the DNA “unzips” and each side is used as a
template to replicate a complete DNA strand…each replicated DNA strand
consists of one new strand and one old strand, this is called semiconservative
replication.
DNA replication is never 100% accurate…some errors in replication occur…if
there is a change the change would be passed on to all subsequent generations.
Mutations.
DNA is organized into chromosomes and is wound around a protein called
histones. Read about how DNA is organized on page249.
Chapter 14 RNA and protein synthesis
Proteins you will remember are one of the important groups of organic
compounds. Proteins are critical to cell life at various times, serving in the
transport of oxygen, cell movement, etc.
Proteins are larger complex molecules composed of amino acids joined by
peptide bonds. Long chains of amino acids are called polypeptides…(pg 254)
While the gene is the fundamental unit of heredity, but DNA does not actually
generate any of the proteins that express genetic messages.
Ribonucleic acid (RNA) acts as a messenger to the protein from the DNA.
RNA synthesis is similar to DNA replication in that the DNA strand unzips and in
a process called transcription RNA is synthesized in the nucleus. The RNA then
detaches from the DNA template and leaves the nucleus. The DNA molecule
“rezips”.
The RNA goes to a ribosome which reads the message and produces a specific
polypeptide chain…this product is called translation.
In RNA thymie is replace by the base uracil. Uracil will link up with adenine like
thymie would. RNA are not double helixes but are single strands. There are 3
main tyes of RNA:
1. Messenger RNA – carries coded instruction fro protein snthesis
2. Transfer RNA – carries specific amino acides to ribosomes during
protein assembly
3. Ribosomal RNA – make up part of the ribosomes.
Pg 255 firefly gene in tobacco plant
Chp 16
Recombinant DNA Technology and Genetic Engineering
Concerns about developing ecologic or health issues with new bacteria.
Page 295 second paragraph “Recent history has failed to bear out these
worries…:
Chp 17 Darwin and Natural Selection
Pg 302
Evolution – genetic changes that occur in a population over time.
Artificial Selection - choosing plants and animasl for breeding based on
characteristics –
Natural selection – pg 306
1.
Overproduction
2.
Variation
3.
Competition
4.
Survival to reproduce
Neo-darwinism or Synthetic Theory of Evolution - emphasizes the genetics of
populations rather than just individuals… more generally accepted than
Darwinism.
Scientific evidence in support of the Theory of Evolution
Fossil Record - bias in the fossil record…fossils are not a random
sample of life in the past because of the conditions which must exist for fossils to
exist.
Comparative Anatomy of different organisms (pg 308, figure 17-7)
Infer the presence of homologous traits in ancestors. Features similar in
structure in different species are said to be homologous
Features that are not homologous but have similar functions are said to be
analagous. (lungs of mammals and trachae of insects)
Analagous organs demonstrate the different ways in which species
adapted to the world…convergent evolution
Vestigial organs…parts that no longer serve and apparent function…in
humans, reduced tail bones, wisdom teeth, muscles that move ears, the
appendix. Whales and pythons have vestigial rear legs. Blind cave dwellers
have vestigial eyes.
Distribution of Plants and Animals – biogeography – evolution of a species
occurs just once…center of origin (a range of origin)
Related species have similar patterns of development – embryos
Biochemical and Molecular Comparisons – the genetic code is universal
(the same amino acid codes occur in different species) and certain proteins
Chapter 18, Microevolution and Speciation
Pg 320
VARIATION…
Population…gene pool includes all possible alleles…where an individual can
have only two possible alleles of a trait…
If a population is not undergoing evolutionary change the frequencies of each
allele will remain constant from generation to generation. Small changes in the
frequency of alleles over several generations are indications of
evolution….microevolution –small gradual changes in a population over time.
Hardy-Weinberg Principle
Genetic equilibrium…not undergoing evolutionary change. Phenotypes
approximately the same from year to year or generation to generation. The
frequency of genotypes can be mathematically determined The Hardy Weinberg
Principle shows that the process of inheritance by itself will not cause changes in
allele frequencies.
In a stable (never occurs in nature) system the proportion of alleles in successive
generations will always be the same as long as :
1. Random mating- mates must not be selected by genotype
2. No mutations –
3. Large population size – model is statistically based so that there must
be a large enough sample…
4. No migration…
5. No natural selection…
EVOLUTION OCCURS WHEN THERE ARE CHANGES IN ALLELE
FREQUNECIES IN THE GENE POOL!
Variation is introduced through mutations.
Genetic Drift – production of random evolutionary changes in small breeding
populations…changes in the gene poll from generation to generation…tends to
decrease genetic differences within a population but increase differences among
different populations.
Founder Effect - Individuals establishing a new colony represent only a small
portion of the gene pool and genetic variation of the original population. This
form of genetic drift is called the founder effect.
Genetic Bottlenecks - Depletion of food supply or disasters
Gene Flow - Migration of individuals is also migration of alleles, gene flow
Natural Selection results in allele frequency changes that increase adaptation to
the environment – natural selection checks the random effects of mutation,
genetic drift and gene flow. Phenotypes “selected” because of advantages in
environment, underlying genotypes go with them…
SELECTION
Note the figure on page 327, Figure 18-4
Stabilizing selection tends to weed out phenotypes at the edges of the
population
Directional selection tends to select for a certain trait toward the edge of a
population, favors one phenotype over another
Disruptive section tends to select for the edges and against the most common
phenotype
GENETIC VARIATION IS NECESSARY FOR EVOLUTION
Genetic Polymorphism –
Genetic Variation by Heterozygous Advantage“Nuetral” Mutations- effect phenotype in small immeasurable ways…
Reproductive Isolation – biological species concept…members of a species
freely interbreed with other members of the species, produce fertile offspring and
do not interbreed with other species in nature.
Isolation Mechanismstemporal isolation (seasonal isolation) (pg 331)
Behavioral isolation (sexual isolation) courtship
signals
Mechanical isolation (parts)
SPECIATION
Allopatric Speciation - geographic isolation over a long period of time (pg 333
Fig 18-10)
Sympatric Speciation –
Chapter 19 Macroevolution and the History of Life
Macroevolution refers to major evolutionary events that occur in groups of
species over long periods of time….large phenotypic changes such as wings, or
the hoof, the thumb, standing…
These new features all are derived from existing structures. An existing feature
is changed in some way which allows the phenotype an adaptive advantage…
How do such changes occur?
Rates of growth determined by regulatory genes…example of infant body
proportions on page 340…
Adaptive Radiation – one or two species expand to fill a variety of ecological
roles “quickly”
Adaptive Zones are new ecological roles or ways of living not previously used by
the organism.. Night flying to catch insects…grazing on grass during migration,
swimming at the oceans surface…see Figure 19-4 on page 342
Adaptive radiation appears to occur more often during periods of environmental
change but it is difficult t determine of changes in the environment “trigger”
adaptive radiation
Mammals existed with dinosaurs but didn’t go through adaptive radiation until
dinosaurs were extinguished…
Is there a cause and effect relationship?
Extinction:
The end of the line…2 types- background extinction and mass extinction
Background Extinction is Continuous low levels of extinction
Mass extinctions of numerous species over a period of time (often followed by
mass speciation)
EVOLUTIONARY CHANGE
Punctuated equilibrium – long periods of stasis (no change) followed by short
periods of rapid speciation
Gradualism – evolution proceeds at more or less a steady rate
LIFE
Life began from nonliving matter in a combination and recombination of simple
molecules into more complex molecules, into macromolecules that were the
precursors of cells.
In the early periods of earth the atmosphere contained little free oxygen, carbon
dioxide, carbon monoxide, water vapor hydrogen and nitrogen made up the bulk
of the atmosphere. Probably contained ammonia, hydrogen sulfide and methane
as well.
Ultrviolet radiation would work to break down the ammonia, methane and
hydrogen sulfide.
Oceans were formed as the world cooled and water vapor condensed and
formed the oceans.
Four requirements of the environment to form life from nonliving matter:
1. No free oxygen – oxygen is very reactive and would break down
(dissolve) the organic macromolecules before life could develop
2. A source of energy- high energy availability in this early earth, electric
storms, radiation, solar radiation, heat from volcanism, etc.
3. Chemical building blocks – water vapor and inorganic compounds
present as ions (to dissolve in water)
4. Time – time for accumulation, and chance (4.6 billion years)
The earliest cells were prokaryotes – fossils found 3.1 to 3.5 billion years ago
Early form of life- stromalites very old but some living stromalites are still
found in hot springs and salt water pools
Early cells were heterotrophs that is they had to find and absorb the
molecules they used for food as opposed to synthesizing them.
Anaerobes – living in a low or no oxygen environment
Autotrophs (make own food from photosynthesis) - cyanobacteria first organisms
to split water to obtain hydrogen necessary to reduce CO2 for food. O2 released
as a by product. Over time O2 accumulates in atmosphere…
Some organisms grew to tolerate and then use oxygen.
ENDOSYMBIONT THEORY - organelles such as mitochondria and chloroplasts
may have originated from a mutually beneficial symbiotic relationship Early
eukaryotes were combination of cells that originally lived apart but that grew to
depend on the relationship with each other…ingested but not digested by the
cell..
FOSSIL RECORD
Geolgoic Time is divided into five eras (Archean, Proterozoic, Palezoic, Mesozoic
and Cenozoic). Each era is divided into periods and periods are divided into
epochs.