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9.7 Option – Genetics: The Code Broken? : 7. Selective breeding and gene cloning
Extract from Biology Stage 6 Syllabus (Amended
October 2002). © Board of Studies, NSW.
[Edit:16 June 09]
Prior learning : Stages 4 and 5 Science, 5.8.2 c) and d) HSC 9.3.3 and 4
analyse and present information from secondary sources to trace the history of the selective breeding of one species for agricultural purposes and use available evidence to describe the series of changes that have occurred in the species as a result of this selective breeding
- Use the information below and information your teacher has given you from secondary sources on the selective breeding of one species for agricultural purposes.
- When you have enough relevant information analyse it so you can organise it in a format that is summarised and shows a logical sequence of events.
- Decide what media you are going to use to present the information and prepare it accordingly.
- Present the information to the class or other audience according to plan.
Some information on relatively recent selective breeding
can be found at Wikipedia 
and
The Open Door Website , Improvements in farming in the
18th Century.
Information on earlier selective breeding can be found at
the University of
Reading , UK. Scroll down to Characteristics of domesticated plants or browse the other headings.
Useful information
Cattle and sheep have been specifically bred for such things as leaner meat, more milk, creamier milk, better quality wool and increased resistance to disease.
Pigs, due to selective breeding are less aggressive, have smaller tusks and more meat compared to their genetically similar ancestors.
Horses have been selectively bred from wild horses over centuries resulting in many varieties including draft horses. These animals include breeds such as the Shire, Clydesdale, Belgian and Suffolk which are used for specific farming purposes, but all involve greater strength, size and ability to pull wagons, ploughs and drays. Race horses also originated from wild horses and have been bred for greater speed.
Plants such as wheat have been bred to grow in harsh environmental conditions, have higher yields and have increased resistance to disease.
explain, using an appropriate example from agriculture, why selective breeding has been practiced
- Selective breeding has been practiced for thousands of years. It involves humans choosing two individuals to mate to produce offspring with certain desirable characteristics, such as leaner meat on an animal or wheat seeds that remain attached to the plant for longer. Many plants and animals for domestic and agricultural purposes have been bred in this way to produce new varieties.
describe what is meant by ‘gene cloning’ and give examples of the uses of gene cloning
- Cloning is the production of a genetically identical gene, cell or whole organism. Gene cloning involves the production of many identical genes.
Human insulin, used by diabetics to control blood sugar levels, is now produced by the cloning of recombinant DNA.
- This process occurs by using special cutting enzymes,
known as restriction enzymes, to cut out the gene for
making insulin from a human chromosome. The enzymes are
also used to cut open a plasmid in a bacterial cell leaving
“sticky ends”. A plasmid is a circular piece of
DNA within the bacterium. The sequence of bases in the open
space in the plasmid matches the ends of the piece of human
DNA. The human DNA is then inserted into the plasmid. The
plasmid (now genetically engineered) is placed back into a
bacterium and is reproduced every time the bacterium
reproduces asexually.
- In this way, the human gene has been cloned. When given
all of the required nutrients, these bacteria will produce
human insulin according to the human genes they contain.
-
In a similar fashion, gene cloning can be used for:
- breaking down toxic waste from oil spills,
- producing a protein that dissolves blood clots,
- introducing pest resistance in some plants like the cotton plant that is now resistant to the cotton boll weevil,
- immunisation against such diseases as cholera and typhoid.
identify data sources, choose equipment or resources, gather, process and analyse information from secondary sources to describe the processes used in the cloning of an animal and analyse the methodology to identify ways in which scientists could verify that the animal produced was a clone
- Data sources you will need to investigate could be web
sites, scientific journals, text books and if available
your teacher may be able to get an appropriate scientist to
speak to the class.
- Choose the most appropriate resources
to obtain the required information.
- Gather the information from your
resources and process it so it can be
recorded in whatever format you have decided on.
- Analyse the information you have
obtained so that you can clearly describe the processes
used in the cloning of an animal. You may choose to use dot
points.
- The last step is to analyse the methodology that scientists could use to verify that an animal produced is a clone.
distinguish between gene cloning and whole organism cloning in terms of the processes and products
- Gene cloning, as described above, involves the
production of identical single genes for specific purposes.
This will transfer copies of single genes from one organism
to another and result in many copies of the gene when those
organisms reproduce. Gene cloning introduces new genes into
a species such as the insulin producing gene in bacteria.
It is also used in gene therapy to treat such diseases as
cystic fibrosis.
- Whole organism cloning involves the transfer of the
entire DNA in a cell to the cloned organism. Dolly the
sheep was cloned by taking the entire DNA from an adult
mammary cell and inserting it into an enucleated egg cell
from a sheep. The resulting cell is now genetically
equivalent to a zygote. This zygote was allowed to
reproduce and the resulting embryo was then implanted into
the uterus of a surrogate mother.
- Dolly was a clone as she was genetically identical to
the entire DNA of the donor sheep via the adult mammary
cell. She contained identical chromosomes and consequently
identical DNA to all the cells in the parent sheep.
- Plants grown from cuttings are actually clones of the original plant as they contain identical DNA throughout the whole plant. Other asexual means of reproducing identical plants include bulbs, corms, tubers, runners and tissue cultures.
discuss a use of cloning in animals or plants that has possible benefits to humans
- Cloning of animals for agricultural purposes is a
genetic refinement of selective breeding. By cloning, the
results are identical to the donor cell, whereas in
selective breeding the resultant offspring may contain some
unwanted genes as well as the desirable ones. The time
involved in producing these desirable cloned populations is
far less than that involved in selective breeding.
- The advantages are similar to those of selective
breeding where large numbers of plants or animals could be
bred for such factors as more meat, more milk, finer wool,
higher crop yield and resistance to disease.
- A disadvantages to all members of a population being genetically identical would be non-resistance to a new strain of disease or changes in environmental conditions, could decimate the whole population as there is no diversity within the population.
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