Download Chapter 21 Artificial Selection Artificial selection is the deliberate

Chapter 21
Artificial Selection
Artificial selection is the deliberate selection by humans of organisms with
characteristics useful to mankind. This selection has resulted in the evolution of a wide
variety of crops and domesticated animals through selective breeding and
hybridisation.
Selective breeding
Variation exists between the members of a species. For thousands of years, people
have selected repeatedly those plants and animals with desirable characteristics to be
the parents of the next generation.
Plants such as cultivated varieties of wheat, barley and potatoes have been bred that
produce higher yields and are more resistant to disease.
Animals Make notes on the characteristics gained through selective breeding in
named animals. P 152 Torrance ‘New Higher Biology’
Make notes on the reason for inbreeding as a selective breeding technique and
explain possible disadvantages.
Make notes on hybridisation as a selective breeding technique and explain the
benefits of hybrid vigour.
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Chapter 21
Bedding Plants (those you plant out in flower beds)
P 154 Torrance
Make sure you fully understand what is being achieved in Fig 21.4
Hybrid vigour in farm animals p154 Read
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Chapter 21
Genetic engineering
Use p155 to define the following terms
Genome :
Genetic engineering (Recombinant DNA Technology) :
Each gene codes for a specific protein (or polypeptide) and genetic engineering
enables a gene that codes for some useful protein in one organism (eg. human) to be
transferred to another organism (eg. bacterium).
Location of Genes
If genes are to be manipulated in genetic engineering, it stands to reason that their
location on the chromosome must be known. Genes can be located using gene
probes or by recognition of characteristic banding patterns.
Banding Patterns Read p155 -156 Torrance ‘Recognition of characteristic banding
patterns on chromosomes’ and make sure you understand what is going on.
Gene probes are short lengths of single-stranded DNA or RNA which are
complementary to a single stranded DNA segment of the gene that the genetic
engineers wish to locate. The probe contains a chemical label such as radioactive
phosphate which will show which segment of DNA contains the required gene.
Make sure you understand what is happening in Fig 21.8 and Fig 21.9 on p157
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Construction of a gene probe (Fig 21.8)
Use of a gene probe (Fig 21.9)
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Chapter 21
Endonuclease enzymes are used to cut DNA fragments at particular points.
[EcoR1 cuts between the G and A in the sequence GAATTC
CTTAAG producing ‘sticky ends’]
Ligase enzymes are used to seal new genes into the genome of other organisms such
as bacteria.
Make notes on these enzymes using information on p157
Use information on p159 to make your own note on the process of genetic engineering
to cover vectors (recombinant plasmids), the use of antibiotics in the selection
process and the use of gene probes. Use note in conjunction with diagram ‘Genetic
engineering’.
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Chapter 21
Production of Human Proteins using Genetic Engineering
Look at diagram whilst reading through this note
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Required gene eg. for insulin, must be located eg. by chromosome banding or
gene probe
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Gene must be cut out using a restriction endonuclease enzyme
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Plasmid must be taken from bacteria
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Plasmid must be cut open using restriction endonuclease enzyme
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Plasmids and fragments including genes are mixed
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Genes insert into plasmids (sometimes) and are sealed by the enzyme ligase
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Plasmids inserted into bacterial cells
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Bacteria cultured and insulin produced in very large quantities
Somatic fusion in plants
Look at diagram whilst reading through this note
Overcomes sexual incompatibility in plants when features of 2 different species are
required to be merged.

Somatic cells from 2 different species are used (ie. not gametes)
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Cell walls digested away using the enzyme cellulase : protoplasts formed
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Chemical treatment or electric current applied. Protoplasts may fuse to form a
hybrid protoplast (somatic cell hybrid) by the process of somatic fusion

Hybrid protoplast treated to induce cell division into a mass of undifferentiated cells
(callus)
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Callus treated with hormones to grow into hybrid plants
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