Download Genetic variation

Variation and genetic technology
Variation
Definition:
All characteristics that differ from organism to organism
Continuous Variation
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Smooth graduation between individuals.
o Eg. Height, hair colour and shoe size
(Think of a histogram from Maths – data fills an entire spectrum.)
Discontinuous Variation
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Organisms either have or do not have a certain characteristic or have one characterstic out of a set of
possibilities.
o Eg. Sex and blood group.
Genetic variation
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During the meoitic division that occurs when gametes are made, homologous chromosomes exchange genes
and then separate.
The chromosomes that are seperated therefore have different DNA to the original parent’s.
Variation has occurred here for the first time. The second time when variation occurs is when male and
female gametes fuse.
As both sets of gametes are different to the parents, the resulting diploid cell contains completely different
DNA to any one of the two parents.
The offspring may inherit certain traits from the parents, but will have a different genotype and therefore a
different phenotype.
Environmental variation
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Also called acquired characteristics as they are not caused by, but may be attributed to, genetic variation
Caused by environmental factors
o Eg. Size of bonsai vs. normal tree as well as intelligence and artistic ability.
Continuous variation is caused mainly by this, but also has a genetic component.
Discontinuous variation has no relationship to this.
Mutation
Definition:
A sudden and unpredictable change in the genetic information
Gene mutation
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Occurs when there is a change in the order of the bases found in DNA/RNA
Results in the sequence of amino acids in proteins
New alleles may result and this may result in variation
Chromosome mutation
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Occurs during nuclear division
Results in a zygote with too many, too few or and abnormal mixture of chromosomes or chromosome
fragments.
Results of mutation
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May be insignificant or cause phenotypic change (very rare)
Phenotypic change may be lethal or give an organism an advantage.
This will be passed onto the next generation and the mutant form may become ‘normal’
(Natural Selection)
Mutations are a source of variation in the population.
Causes of mutation
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Chemical substances and radiation
Called MUTAGENS and include:
o Ultra-violet (from Sun)
o X-rays
o Gamma, alpha and beta particles (from radioactive decay)
o Nitrous acid and tars
o Hydrocarbons from car exhaust fumes (Catalytic converters required)
NOT all will cause mutations but WILL increase the rate at which mutation occurs.
o Debate about nuclear power industry + some radiation very dangerous.
Down’s Syndrome
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Caused my chromosome mutation during meiosis
During development of ovum a chromosome pair fails to split, therefore resulting in one extra chromosome
number 21.
Results in flattened face, slanted eyes, below average height and intelligence.
Life expectancy reduced due to susceptibility to diseases such as leukemia and heart disease.
Generally very affectionate and contented.
Genetic Technology
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Genetic technologists change the genotypes of cells in organisms by taking genes from one organims and
putting it in another.
This gives the acceptor new capabilities.
New varieties of organisms can be used to manufacture useful chemicals.
Insulin production
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Insulin, for people suffering from diabetes mellitus, can be produced by genetic technology
The human insulin gene can be inserted into a bacterium and in this way, insulin can be synthesised.
o The ‘modified’ bacterium is known as the transformed bacterium.
The following sequence is carried out:
1. The insulin producing gene is found
2. An enzyme called a restriction endonuclease is used to extract the insulin gene from human cells.
a. Breaks up DNA into smaller pieces
b. The piece that contains the insulin gene is extracted and purified
3. The gene is transferred to another cell where it takes over the production of protein molecules.
a. The bacterium Escherichia coli is commonly used.
b. Special enzymes cut open the loop of the plasmid to form a strand.
c. This strand is mixed with the insulin genes to form recombinant DNA.
d. The enzyme ligase joins the plasmid together again.
e. The transformed plasmid is inserted into the bacterium and acts as a vector.
4. The host cells multiply and produce insulin in response to the new DNA.
Cystic fibrosis
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Like the plasmid utilized in insulin production, a virus can also be used as a vector.
Cystic fibrosis causes overproduction of mucus.
The normal gene for mucus production can be added to a human virus.
The sufferer is then exposed to this virus, which passes on the normal gene to the sufferer.
There have been problems, but the technique seems to work well.
Genetic technology in agriculture
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Genes are introduced to crop plants to enable them to produce specific chemicals that make the plant
resistant to attack by fungi or insects.
This means that less pesticide needs to be used, and therefore pollution can be reduced.
A gene for herbicide resistance could be introduced so that crop fields could be sprayed with herbicides to
kill all the plants except for those with that gene.
Genetically modified fruits and vegetables can be made to increase ripening time to increase shelf-life and
thereby avoid wastage etc.
Problems that may result from use of genetic technology:
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New, disease-causing and antibiotic-resistant bacteria may develop accidentally.
Bacteria may develop increased virulence, which means that it can spread more easily, and therefore more
quickly.
There are greater possibilities for the development of biological weapons for war, and therefore a threat is
posed to humanity.