Transcript 20.1.1 Hybridisation

Blueprint of Life
Topic 20: Hybridisation
Biology in Focus, HSC Course
Glenda Childrawi, Margaret Robson and Stephanie Hollis
DOT POINT(s)
 process information from secondary sources to
describe an example of hybridisation within a species
and explain the purpose of this hybridisation.
Introduction
The term reproductive
technology applies to any use
of technology to assist and
improve reproduction. Current
reproductive technologies and
genetic engineering are the
culmination, over many
hundreds of years, of the efforts
of humans to improve the
quality and yield of their food.
www.emirates247.com
Introduction
At first, humans obtained food by hunting and gathering; they
then began raising their own animals and growing their own
crops and soon realised the advantage of selecting seeds from the
best crops and breeding the best quality animals, to improve the
quality and yield of future generations.
wildyogini.wordpress.com
Introduction
This was the start of selective
breeding or artificial selection,
involving the human
‘manipulation’ of living
organisms by selecting those
which should breed, ensuring
they pass on their favourable
characteristics.
www.dirtbrothers.org
Introduction
The trend to ‘manipulate’ the
phenotype of offspring to achieve
desirable characteristics has continued
over many hundreds of years,
becoming more sophisticated as
technology has improved. The older
techniques of artificial pollination
(plants) and selective breeding are still
used, together with modern-day
reproductive technologies which
include artificial insemination
(animals), in vitro fertilisation, embryo
transfer and cloning, amongst others.
abcmedicaltourism.com
Introduction
This advanced technology allows more specific selection and
breeding, and has led to the even more advanced technology of
inserting desired genes into organisms by genetic engineering.
Genetic engineering is only considered a reproductive technology
if the gene being inserted has the effect of assisting reproduction
(e.g. increasing fertility).
www.earthtimes.org
Introduction
The manipulation made by
humans using reproductive
technologies is a contentious
issue, raising ethical
considerations—an area of
study known as bioethics has
developed to help people make
wise decisions when important
values are at stake.
www.sju.edu
Introduction
The advanced technologies such as cloning and genetic
engineering make it much easier for humans to tamper with the
human genome and recombine genes of different species. This
raises issues of human rights and animal rights and also how
‘tampering with nature’ may alter the path of evolution as a
result of using these technologies.
b4tea.com
Hybridisation
The term hybridisation means
the crossbreeding of two
genetically non-identical
individuals. This may mean
crossing parents of the same
species, who show genetic
variation (intraspecific
hybridisation), or it may extend
to parents of different species
(interspecific hybridisation).
www.peg.ethz.ch
Hybridisation
We are now going to look at
examples of hybridisation within a
species (intraspecific). Within the
units classified as species, there are
populations that may be more or
less distinct from each other. These
groups are called ‘races’ or, more
scientifically, subspecies or varieties.
When discussing hybridisation students
are expected to describe intraspecific
hybridisation of varieties or subspecies,
not hybridisation between species.
www.anbg.gov.au
The Purpose of Hybridisation
Hybridisation involves cross-breeding as opposed to in-breeding.
It occurs both in nature and artificially (e.g. as a result of human
manipulation of breeding—known as selective breeding). Crossbreeding or hybridisation is commonly used in horticulture and
agriculture to improve the quality of the plants and animals being
grown or raised.
www.jerseydairy.je
The Purpose of Hybridisation
Selective breeding occurs at two
stages in the hybridisation
process:
■ selecting parent individuals
with desirable traits and then
breeding them in the hope that
some offspring will inherit a
combination of these desirable
traits
■ selecting offspring that reflect
the desired combination of traits
for further breeding.
knoji.com
The Purpose of Hybridisation
The result is the production of
hybrid offspring with combined
traits that make them better
suited to their environment or
to meet their end use (e.g. bigger
flowers, higher nutrient value,
increased crop yields, more suitable
breeding time, greater resistance to
drought or disease or salinity and
higher stamina).
nlevel-studynotes.blogspot.com
The Purpose of Hybridisation
Successful hybridisation leads to
hybrid vigour —increased
strength, better health and greater
fertility in the hybrid individuals than
is usually found in the homozygous
individuals from which they were
bred. Hybrids often display
advantages that are not present in
either of the parental varieties, as a
result of the compounded effects of
their new gene combinations, giving
new phenotypes on which natural
selection can act.
science-at-home.org
The Purpose of Hybridisation
Advantages of hybridisation
■ It increases genetic variety.
■ It may combine the best feature
of each parent, resulting in hybrid
vigour.
thecaudallure.blogspot.com
The Purpose of Hybridisation
Disadvantages of hybridisation
■ It may combine the weaker features of each parent and the
offspring would have less stamina, less resistance to disease or
changes in the environment, lower crop yields, and so on.
■ It is a costly procedure, especially if the resulting offspring do
not display hybrid vigour.
■ Sometimes the hybrid offspring are infertile or have reduced
fertility (they may be heterozygous for some genes where the
homozygous condition gave a breeding advantage to the parent
generation).
evolution.berkeley.edu
The Purpose of Hybridisation
■ Hybridisation is often followed by selective interbreeding of
the resulting hybrids with each other to maintain the favourable
combination of traits within the population. This equates to inbreeding the hybrids and negative effects may become apparent in
other traits; e.g. in chickens that have been cross-bred to create a
high clutch yield (increased egg laying), subsequent in-breeding
of these hybrids has resulted in eggs with very thin shells that
break easily.
evolution.berkeley.edu
An Example of Hybridisation
In 1870, William Farrer (a 25year-old mathematics graduate and
medical student) moved to
Australia from England. He was
employed by the Department of
Lands in the Dubbo to Cooma
districts and later began
farming.
en.wikipedia.org
An Example of Hybridisation
Farrer was aware that wheat
growing in Australia was
presenting problems—the
strains being grown (in
particular the English varieties)
were not suited to the harsh,
dry environment, were
susceptible to disease such as
rust, matured early and the
grain quality was not of a high
enough standard for milling and
baking.
www.nma.gov.au
An Example of Hybridisation
Farrer’s selected two different
varieties of wheat, each
containing a desired trait for
growing in Australia’s harsh
conditions.
■ Indian wheat was droughttolerant and resistant to some
diseases.
■ Canadian Fife wheat matured
late and had the best milling and
baking qualities.
www.commodityonline.com
An Example of Hybridisation
Farrer hybridised these two varieties and then selected plants that
had the advantages of both parents, to produce many hybrids, of
which one was the Bob’s variety, the first commercially grown
wheat variety in Australia. He also created a Fife–Indian wheat
variety called Yandilla from these parent varieties.
exhibitions.senate.gov.au
An Example of Hybridisation
Another extremely successful
hybrid was the result of his cross
between a Purple Straw variety,
14A, and his a Fife–Indian wheat
variety Yandilla. This resulting
variety called Federation (named in
1901) had the hardiness of the
Indian variety, a tendency to escape
rust disease and short, strong straw
that made it ideally suited to the
Australian climate and harvesting
methods.
www.brisbanetimes.com.au
An Example of Hybridisation
Farrer’s wheat hybridisation success was evident when, by the
year 1914, 22 varieties out of the 29 grown in New South Wales
were Farrer wheats. Farrer’s studies also contributed to an
understanding that factors such as diseaseresistance, grain quality
and maturing time in wheat can be inherited.
www.vision.net.au
An Example of Hybridisation
Today, hybridisation and selective breeding still play a role in
agriculture in Australia, along with advanced biotechnological
techniques such as cloning and genetic engineering to create
transgenic species.
www.weewaa.com
The DOT Point
The word species in Latin means ‘kind’, as used in ‘different
kinds’ of organisms. A species is a group of organisms that can
interbreed and give rise to fertile offspring (that is, offspring that
are able to reproduce).
www.allaboutwildlife.com
The DOT Point
Therefore to address hybridisation within a species (intraspecific
hybridisation as opposed to interspecific hybridisation), the selection of
examples should not include creatures such as mules or any other
hybrids across species.
www.tripwiremagazine.com
The DOT Point
Examples that meet the criteria
of this dot point are:
■ corn hybridisation
■ grape hybridisation
■ cattle breeding (e.g.
Hereford Angus)
■ seedless watermelons
■ dog hybridisations (e.g.
labradoodles).
www.labradoodle.net.au
The DOT Point
Examples that do not meet the
criteria (that is, examples of
hybridisation between species)
are:
■ donkey X horse =
mule/hinny
■ tiger X lion = liger/tigon
■ cabbage X radish = rabbage
■ emmer wheat X goat grass =
common wheat.
daisy-jayne.deviantart.com
Activity/Homework
-Students to answer the following questions in their notebooks.
1. What is meant by hybridisation?
2. Describe an example of hybridisation within a species and
explain the purpose of this hybridisation.
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