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CHAPTER 24
REVIEW QUESTIONS
24.1
a.
b.
c.
Artificial selection: a breeding program controlled by humans to produce desirable
characteristics in offspring.
Inbreeding: artificial selection to produce consistency of particular characteristics by
mating close relatives.
Outbreeding: artificial selection to produce a particular characteristic by mating closely
related varieties or species.
24.2
The grain is strongly attached to the stalk and thus natural methods of dispersal (commonly
wind in grasses) could not occur.
24.3
Carnivores do not usually occur in large groups and are often very territorial – thus behaviour
patterns would have precluded them being kept together in a relatively small area. Provision
of food would have created a further problem.
24.4
Natural selection depends upon selection pressures for a particular trait and this usually
involves changing environmental conditions. Thus unless there is a particular change that
drives the selection for a particular type of trait, the number of individuals exhibiting the trait
will remain at a relatively stable size. Random mating increases the chance of variability in
offspring.
24.5
Production of cheese, yoghurt, leavened bread, alcoholic beverages.
24.6
Methanogen bacteria are decomposers that release methane gas as a byproduct of their
metabolism. Sewage and other human biodegradable waste can be decomposed in a digestor
unit and the gas collected to be burned for cooking or to produce electricity.
24.7
An antibiotic is a chemical (usually produced by a microorganism) that prevents the spread of
other microorganisms by either suppressing their growth or killing them.
24.8
Decreases competition for resources such as food and space.
24.9
A narrow-spectrum antibiotic is only effective against a few specific bacteria whereas a broadspectrum antibiotic inhibits the growth of a large number of different types.
24.10
It is now possible to genetically manipulate microorganisms at a rate faster than the
development of vaccines to counteract their effects. With increased fast mobility of humans
from one area to another, infected individuals could spread the pathogens into populations not
intended for infection. Spread of pathogens is indiscriminate and so large numbers of nontarget individuals (e.g. young children) could be killed.
24.11
The oral contraceptive contains progesterone and oestrogen. Natural progesterone inhibits the
release of FSH from the anterior. FSH. stimulates the development of a primary oocyte and
the production of oestrogen in ovarian tissue. With no FSH a mature ovum will not be
produced and thus no pregnancy will result from copulation.
24.12
DES is an artificial oestrogen. The endometrium is maintained by both progesterone and
oestrogen thus administration of only DES would not have aided maintenance of the
pregnancy of the problem was associated with endometriosis. Rat experiments demonstrated
that proper fetal development required a certain level of oestrogen. However at high levels it
caused abnormalities. Thus administration of DES is more likely to cause developmental
problems which usually results in miscarriage.
24.13
The male oral contraceptive initially involved blocking production of gonadotropins (which
stimulate sperm production) in the anterior pituitary gland. These hormones also are
responsible for testosterone production by the interstitial tissues of the testes. Thus males on
the pill experienced enlargement of the prostate gland and decreased masculinity and sex
drive.
24.14
A totipotent cell is totally undifferentiated and thus capable of growing into any other type of
cell of that species.
24.15
Callus cells are aggregates of undifferentiated plant cells. A protoplast is a callus cell from
which the cell wall has been removed by enzyme treatment.
24.16
Protoplasm fusion between different types of cells cannot be achieved when cell walls are
present. Reproduction between different species to form hybrids is blocked by a variety of
intrinsic isolating mechanisms. Thus production of protoplasts of different species allows
fusion of their protoplasm. Since protoplasts are completely undifferentiated, the fused cell
can be chemically induced to form cell walls and grow into a new hybrid individual having the
characteristics of both species.
24.17
Shikonin (a silk dye), codeine, atropine, quinine, pyrethrin, menthol, digitoxin.
24.18
Viruses cannot reproduce by themselves – their DNA instructs a host cell to produce more
viruses.
24.19
Cultured animal tissues are infected with a specific virus, e.g. for poliomyelitis. When
adequate viruses are formed by the culture cells they are separated by filtration and killed. The
dead virus is packaged into the vaccines. (These dead viruses will bring about an immune
response and the formation of memory cells without causing the disease. Thus the vaccinated
individual develops artificial acquired immunity to the pathogen.)
24.20
Monoclonal antibodies are antibodies which are specific to a particular antigen. A specific
antigen is injected into a mouse or rabbit causing its b lymphocytes to produce the specific
antibody to that antigen. The lymphocytes are isolated and extracted from the animal’s spleen
and inserted into rapidly growing tumor cells in a culture medium. The resulting fused
hybridoma cells produce large amounts of the antibody which can be extracted and purified.
Monoclonal antibodies are used in both diagnoses (e.g. pregnancy) and treatment of disease.
24.21
The nucleus of an egg cells is removed and replaced with a diploid nucleus from a somatic cell
that has been induced to ‘forget’ its specialisation. Fusion of the enucleated egg cell and the
diploid nucleus is achieved by an electric jolt which also triggers cell division. The cell mass
is then transferred to a surrogate mother to complete development.
24.22
A fertilised egg is cultured to form a mass of cells called blastomeres surrounded by a
covering pellucida. The blastomeres are removed through the pellucida. Each cell is given a
new artificial pellucida and allowed to form another mass which is then transferred to a
surrogate mother to complete development.
24.23
Because blastomere separation results from a fertilised egg there will be more genetic
variation and thus reduced chance of achieving the desired trait than in cloning using nuclear
transfer of a known genetic combination.
24.24
A stem cell is a precursor cell that can potentially grow into a variety of different types of
cells.
24.25
Although all stem cells can differentiate into different types of cells, the extent to which they
can do so becomes limited as they themselves start to differentiate. Thus totipotent stem cells
can become any other types of cell (they are completely undifferentiated) and a new organism
whilst the partially differentiated pluripotent stem cells can form into a large variety cells but
not a new organism. Multipotent stem cells are even more differentiated and can only produce
a limited number of types of cells.
24.26
Most adult stem cells are multipotent whilst embryonic stem cells are pluripotent.
24.27
The production of cloned embryos developed from adult cells to extract stem cells which
could be induced to form a range of tissues which can be used to treat a particular condition of
the original donor.
24.28
Transdifferentiation is a process which induces one fully differentiated cell type (e.g.
fibroblasts) to be converted into an entirely different cell type (e.g. nerve cell) in culture
conditions.
24.29
Nuclear polymerase: an enzyme involved in the synthesis of nucleic acid molecules.
Restriction nuclease: an enzyme that breaks the DNA molecule at a particular base sequence
(DNA scissors).
Ligase: an enzyme that binds DNA molecules together (DNA glue).
24.30
Sticky ends of the DNA molecule occur when a restriction nuclease cuts each chain of the
DNA molecule asymmetrically, so that each fragment has protruding ends composed of
unpaired bases. They readily bond with other fragments with complimentary unpaired ends.
Thus in crossing of homologous chromatids during meiosis, restriction nucleases break the
chromatids at recognition sites that produce sticky ends. Recombination with swapped pieces
of chromatid is thus rapidly achieved and mediated by ligase.
24.31
a.
b.
c.
d.
e.
f.
24.32
Because the particular gene is not normally expressed in the bacterium, insertion of a promoter
gene ensure its expression and thus formation of the required chemical.
24.33
An organism that carries genes from another organism.
24.34
The tough cellulose walls of plant cells make it more difficult to insert foreign genes.
24.35
Production of protoplasts from callus cells.
Shooting minute gold pellets coated in recombined DNA into cells.
Perforating the cell wall by shaking the cells in a solution of silicon carbide.
Infecting with a genetically modified plant pathogenic bacterium.
24.36
Concern that marker antibiotic resistant genes can be passed on to the consumer – could be
valid.
New proteins could cause a toxic or allergic response in the consumer – unlikely since the
proteins would be broken down during digestion and should not affect non-sensitive
consumers.
GM food may contain allergens from other species – valid for sensitive people.
Herbicide-resistant GM plants may incorporate some of the herbicide in their tissues and this
could be magnified in consumers – valid: not enough is known about long-term effects.
Ethical concerns regarding the source of transplanted genes, e.g. vegans and various religious
groups.
Contamination of non-GM crops and wild species through cross pollination – valid
particularly when the GM crop is farmed.
24.37
The DNA strand is induced to unzip by heat treatment to produce single nucleotide chains.
Short primer single chains are added that bind to complementary bases of the unzipped strand.
Polymerase and nucleotides are added – produces copy of the nucleic acid from starting
sequences made by the primers.
restriction
vector
DNA ligase
mRNA
bacterial
insulin
24.38
Variation of the primers of known DNA sequences used can lead to the rapid detection of
particular types of DNA thus gene locations and functions (the primers can be produced using
reverse transcription from mRNA of a known protein).
24.39
Identification of gene location and function, detection of infectious disease organisms, genetic
screening, genetic fingerprinting.
24.40
In the human genome there are regions of extremely variable DNA, called hypervariable
regions. Each individual varies uniquely (except for identical twins) in the number of times
each sequence is repeated at one place, thus forming a genetic fingerprint. Comparison of
hypervariable sequences of a DNA strand from an unknown source with DNA from known
individuals can therefore be used in the identification of the source.
24.41
a. Hypervariable region: a short region of variable DNA of fixed base sequence that is
repeated many times.
For any individual the number of times these sequences is repeated
is constant at any location.
b. Gel electrophoresis: an electric current is passed through a gel on which e.g. DNA
fragments are placed.
Each fragment moves through the gel at a different rate to produce
a banding pattern.
c. Southern blotting: a techniques in which the banding pattern on the gel is transferred to
nitrocellulose
paper.
d. Autoradiography: exposure on nitrocellulose paper (film) of radioactive probes by light.
e. DNA hybridisation: formation of complementary DNA chains using nucleotides
containing radioactive
probes.
24.42
To map and analyse the nucleotide sequences of each human gene.
24.43
Recombinant alleles.
Reverse transcription from known mRNA.
Gel electrophoresis to separate the bands of DNA each of which can be analysed for
nucleotide sequence.
Bacterial recombination and study of the expression of the inserted DNA.
24.44
A specific mRNA is isolated. Radioactively labelled DNA nucleotides are introduced to form
a complimentary chain of DNA (cDNA) which can then be subjected to PCH techniques to
determine its position along a chromosome.
24.45
Regulator genes.
24.46
Somatic gene therapy – insertion of the normal genes into diseased tissue.
Germ line therapy – replacement of defective with normal genes in gametes.
24.47
Retroviruses do not have DNA but RNA. Reverse transcription occurs in the host cell to
produce the cDNA. This then acts as the template to form a strand of DNA. The retrovirus
RNA is then degraded and the new DNA permanently inserts into the host cell DNA.
24.48
A technique which enables identification of expressed genes by formation of cDNA from
mRNA in cells and comparison of the cDNA with known DNA nucleotide sequences.
24.49
Particular cells produce particular types of proteins.
Each protein has a primary structure of a set number of amino acids in a particular sequence
forming a polypeptide chain.
The sequence of nucleotides in the polypeptide chain is determined by the sequence of codons
on mRNA.
mRNA is formed during transcription from a part of a chain of the DNA strand when it
unzips.
cDNA can be formed from mRNA.
If labelled nucleotides are used in the formation of cDNA, the complementary location on a
DNA chain can be located.
24.50
No – only those genes that are expressed.
24.51
Comparisons between the DNA of a recently infected person can be made with the DNA from
several patients who have shown successful responses to different treatments to determine the
most appropriate treatment for that person.