Chapter 21 Artificial Selection Artificial selection is the deliberate ...

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11 Δεκ 2012 (πριν από 4 χρόνια και 11 μήνες)

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Chapter 21

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1

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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 breedi
ng 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 Hi
gher 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.


Chapter 21

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2

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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




Chapter 21

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3

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Genetic engineering


Use p155 to define the following terms


Genome :



Genetic e
ngineering (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 P
atterns
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




Construction of a gene probe
(Fig 21.8)



Use of a gene probe
(Fig 21.9)




Chapter 21

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4

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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 engine
ering
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’.



Chapter 21

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5

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Production of Human Proteins using Genetic Engineering



Look at diag
ram
whilst reading through this note




Required gene eg. for insulin, must be
located

eg. by chromosome banding or
gene probe




Gene must be
cut

out using a restriction
endonuclease

enzyme




Plasmid must be taken from bacteria




Plasmid must be cut open using
restriction
endonuclease

enzyme




Plasmids and fragments including genes are
mixed




Genes
insert into plasmids

(sometimes) and are
sealed

by the enzyme
ligase




Plasmids

inserted into bacterial cells




Bacteria cultured and insulin produced in very large quan
tities




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
game
tes)



Cell walls

digested away using the enzyme
cellulase : protoplasts
formed



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
)



Callus treated with hormones to grow into
hybrid plants