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AS 91607 (3.7)
Demonstrate Understanding of
Human Manipulations of Genetic
Transfer and its Biological
Implications
Internally Assessed, 3 credits
Reference Text – ESA Study Guide,
chapter 24
Whole Organism Cloning
o Refers to the production of genetically identical whole
organisms (clones).
o It involves growing a whole organism from one cell taken
from the organism (“parent”) that is being cloned.
o Cloning is designed to quickly and cost effectively get many
identical copies of an organism with desirable traits,
especially transgenic organisms.
Biological Implication
The resulting cloned population lacks genetic diversity
compared with other populations.
Biological Implication
Gene expression can be influenced by factors in the internal
environment of the animal (epigenetics)
Eg the amount of protein or trace elements in the diet.
A cloned animal may not be identical to the original parent.
Eg clones typically vary in colour patterns compared with
the parent and with one another.
Cloning may also be used in conservation.
Eg cloning the surviving members of an endangered species
to increase the population reduces the chances of extinction.
In NZ, the last members of the Enderby Island breed of
cattle (a cow “Lady”) was cloned in 1998 (producing a
daughter “Elsie).
It has even been proposed that cloning could be used to
bring extinct species, such as woolly mammoths “back to
life” (“de-extinction”)
Reading – Enderby Island Cattle
While Elsie is genetically identical to Lady, her colour patterns
are similar but not identical.
A son, “Derby” had also been born to Lady, as a result of
embryo transplantation using semen recovered from Enderby
Island during the culling of the cattle (culling was carried out
in the early 1990’s for conservation purposes.
Cloning has also been proposed for a beloved pet (either
before or after death), the cloning of famous animals has
such as the long dead NZ racehorse “Phar Lap” (“Big Red”)
Phar Lap @ Te Papa Museum
Animal Cloning
Cloning whole vertebrate animals from adult donor cells is a
more complex process.
Because adult animal cells are specialised in that only genes
related to that cell’s functions are normally expressed.
However, the creation of Dolly, the cloned sheep, in 1997
from the udder cells of a Finn-Dorset ewe showed that it is
possible to reprogramme an adult cell to generate an entire
organism, and clones of many animals including sheep, mice,
rhesus monkey, cattle, dogs, goat, camels and wolves have
been produced over the past two decades.
The usual method for cloning
animals involves somatic cell
nuclear transfer (SCNT).
Dolly was a female domestic
sheep, and the first mammal to
be cloned from an adult somatic
cell, using the process of nuclear
transfer. Wikipedia
Born: July 5, 1996, Scotland,
United Kingdom
Died: February 14, 2003
Species: Ovis aries
Children: Bonnie, Rosie, Lucy,
Sally, Darcy, Cotton
SCNT video
SCNT
Nucleus from the donor adult somatic cell is transferred into
an enucleated egg cell (nucleus has been removed or
destroyed by UV light).
A pulse of electricity fuses the two cells together
(“fertilisation”) and the resultant egg is allowed to divide
under artificial conditions for around 5 days. This is now
known as the blastocyst.
The blastocyst is then implanted into the uterus of a
surrogate female for development, growth and repair.
Biological Implications – Whole Organism Cloning
Biological implications of cloning include possible impacts on:
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Genetic diversity
Ecosystem
Evolution
Health & survival of individuals
Health & survival of populations
Impact on Genetic Diversity
Cloning produces individuals that are genetically identical
(including sex). A cloned population is less likely to survive
on environmental change, especially the introduction of a
new pathogen. Any species brought back to life may not
walk the Earth again for any length of time – there could be
a series of extinctions ad re-extinctions.
Impact on Evolution
Any population derived from a clone will have little or no
genetic diversity. This greatly increases the risk of “reextinction”
Impact on Health
If the genome of the cloned individual contains contains
alleles for genetic disorders, the clones inherit this disorder.
Impact on Ecosystem
Monocultures are plants that very similar, or identical
genetically.
A large population of cloned plants could be considered an
extreme example of monoculture.
Researchers would need to consider the following when analysing the
possible impact on ecosystem from de-extinction:
Will the cloned species be able to reoccupy its original niche within the
biological community?
Or adapt to a new niche?
Is the original still available?
Will the cloned species out-compete existing members of the community,
and/or disrupt food chains and/or cause local extinctions?
Will the cloned species be out-competed by the existing species?
Will food supplies still be in existence and sufficient for the cloned species to
survive?
Will clones be dependent on human management for their survival, that’s is,
have to occupy a managed ecosystem rather than a natural ecosystem?
When it coms to cloning extinct organisms, we definitely need to proceed
with caution.
Another method that has been used since the
1980’s to produce animal clones is that of
embryo splitting or embryo twinning.
Embryos at a very early stage of
development, say around 8 cell stage are still
totipotent
– are split to produce identical twin embryos
that are then inserted into a female animal
for development.
Reference
http://animalscience.ucdavis.edu/animalbiotech/images/Image5.gif
De-extinction “Bringing them back to Life”
Each year an estimated 10 000 to 100 000 animal species die
off, joining the countless species that have gone extinct
throughout the Earth’s history!!! Extinction is
forever………..maybe not anymore!!!!
Scientists are close to bringing extinct species back to life
“de-extinction”.
This involves finding & extracting DNA from preserved tissue
remains (usually from being frozen).
A single cell or intact nucleus may be sufficient, and
sequencing the DNA to obtain a complete (or sufficiently
complete) genome.
This may involve amplification using PCR technique.
The cloning then follows the process of SCNT, using a suitable
surrogate female, typically a close living relative.
Eg a host for cloning a woolly mammoth would be a female
elephant, most likely an African elephant, as they are larger
than Asian elephants so closer in size to the extinct
mammoths.
Pyrenean ibex
The first attempt at de-extinction was made in 2003 when
scientists cloned the Pyrenean ibex which had become
extinct in 2000.
The clone only lived a few minutes, but recent advances
(including the ability of scientists to manufacture DNA to
order) means the chances of the clone surviving are greatly
improved.
In January 2013, Australian scientists announced they had
developed embryos of the gastric brooding frog which had
become extinct in the 1980’s.
Note – just because we can bring species back from the
dead, doesn’t mean that we should. There are many
potential biological implications concerned with cloning
extinct species.
Gastric Brooding frog
Readings
The Microbial World: Biology and Control of Crown Gall
(Agrobacterium tumefaciens)
Plant Transformations using Agrobacterium tumefacians
Videos
Ti-Plasmid animation
Gene Transfer in Plants using Ti-Plasmid