Human intervention in
evolution
Chapter 16 – Part 1
Selective Breeding
 Selective breeding is the process of breeding plants
and animals for particular genetic traits which are
desirable.
 This is achieved in animals by using male animals with
the desirable traits for a number of generations until
the undesirable traits die out in the population.
Selective Breeding: Australian
Sheep
 Selective breeding is an integral part
of the Australian wool industry.
 Selective breeding has been used to
increase the amount of wool a sheep
produces and also to reduce the
diameter of the wool fibres.
 Selective breeding among sheep is
achieved by breeding ewes with rams
that have the desired traits.
Selective Breeding: Australian
Cattle
 Selective breeding has also been used with cattle in Australia
in order to increase milk yields among dairy cows.
 The modern dairy cow can produce about 35-50 litres of milk
per day. This is about ten times more milk than a calf would
ever need.
Reproductive technologies
 There are many reproductive technologies associated
with selective breeding.
 This includes:
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Artificial Insemination (AI)
Embryo transfer in livestock (MOET)
Sex selection through sperm sorting
Multiple ovulation and embryo transfer
Oestrous synchronisation
Artificial Insemination (AI)
 Artificial Insemination involves collecting semen from a
selected male and then introducing this into the
reproductive tract of a female.
 The advantages of AI are
 A single volume of ejaculate from a male can be sufficient
to fertilise a number of eggs.
 Female can be fertilised by sperm that has come from
other regions and even other parts of the world.
 A male’s ejaculate can be used long after it has died.
Genetic Impact of AI in animal
breeding
 By using semen samples from selected animals, genetic
variability is reduced among populations.
 If random mating was allowed to occur, then a greater
variety of traits would exist.
 The widespread use of AI could result in the loss of
undesirable traits and also expose animals to a greater
susceptibility to diseases that they would otherwise have
built up a resistance against.
Embryo transfer in livestock
(MOET)
 Multiple Ovulation and Embryo Transfer (MOET), allows
more desirable females to contribute a greater amount
of gametes.
 Multiple ovulation refers to the process where the
female animal receives injections of follicle stimulating
hormone (FSH) in order produce a greater amount of
eggs when she ovulates.
 Embryo transfer involves transplanting fertilised
embryos into surrogate mother.
Sex selection through sperm
sorting
 In some agricultural industries, being able to select the
sex of the offspring is an advantage for farmers.
 This can now be done by dying sperm with a
fluorescent dye and separating out the sperm with Xchromosomes from the sperm with Y-chromosomes.
 This is especially important in the beef industry where
males are preferred and also in the dairy industry
where females are preferred.
Manipulating breeding cycles
 This involves the synchronisation of the oestrus cycles of female
animals.
 NOTE: animals can only become pregnant if they are inseminated
during oestrus.
 This is important for the MOET procedure (discussed earlier).
 It also allows for higher rates of fertilisation and births.
 The synchronisation of oestrus is achieved by the introduction of
the hormone progesterone to the female. This can be introduced
through:
 The animal’s diet
 Skin implants
 Vaginal implants
 Once the source of progesterone is removed, the animal begins
oestrus within 3 days.
Artificial pollination in plants
 Artificial pollination has been used for centuries.
 This was the basis of Gregor Mendel’s pea experiments.
 This process involves:
 Removal of unripe stamens from plant to be fertilised.
 Protection of the stigma of the selected female plant from
stray pollen.
 Collection of pollen
 Transfer of pollen to the stigma of the female plant.
Creating Hybrids
 Artificial pollination can be used to create hybrid plants.
 For example wheat and rye can be crossed together to
create a hybrid (like a horse and donkey produces a
mule).
 This hybrid is infertile.
Cloning
 Cloning is a form of asexual reproduction.
 This involves the genetic information required for a
new individual originating from only one parent.
 There are different types of cloning techniques. For
example:
 Cloning by embryo splitting
 Cloning by nuclear transfer
Embryo Splitting
 Embryo splitting involves removing an embryo from an
individual.
 Individual cells from this embryo are removed and then
placed into Petri dishes that contain the correct
nutrients and hormones for growth.
 Each of the removed cells now divides to form a new
embryo.
 These embryos are then implanted into the uterus of
surrogate mothers. These surrogate mothers will then
give birth to identical offspring.
Cloning using nuclear transfer
techniques
 There are many different ways to manipulate cells and
their nuclei. For example, you can:
 Remove the nucleus from a cell, enucleated.
 Transfer the nucleus from one cell to an enucleated cell.
 Fuse a somatic cell with an enucleated cell
Dolly the Sheep
 Dolly the sheep was created using a somatic cell from
her mother and fusing this with an enucleated egg cell.
 Once the egg cell showed evidence of early embryonic
development, it was transferred into the uterus of a
surrogate animal.
Cloning: the downside
 Success rate of cloning is very low.
 Hundreds of embryos often need to be implanted into
females in order to successfully end up with a growing
embryo.
 Each time mammalian cells divide, the telomeres on the
ends of chromosomes get shorter. It is thought that this is
the cause of aging. So therefore cloned animals would age
rapidly.
 This has been evidenced in Dolly the sheep. She had to be
put down at age 6 because of lung problems and severe
arthritis.
Cloning Plants
 This can be naturally or artificially done.
 Examples of natural cloning are: cuttings, runners,
suckers, etc.
 Artificial cloning of plants involves the culturing of a
piece of adult plant.
 This can then be divided further to create a large
number of cloned copies of the plant.
 All of the resulting individuals are genetically identical.