Demonstrate understanding of human manipulations of genetic transfer and its biological implications
1
Human
manipulations of genetic transfer may involve:
·
selective breeding (could include embryo
selection, animal breeding, plant breeding, development of new crops)
·
whole organism cloning
·
transgenesis
·
investigation and modification of the expression
of existing genes.
2
Biological
implications may involve the impact on:
·
ecosystems
·
genetic biodiversity
·
health or survival of individuals
·
survival of populations
·
evolution of populations.
SELECTIVE BREEDING
Natural Selection vs Selective Breeding (Artificial Selection) - An Introduction
Since Charles Darwin first coined the term, natural selection has been understood to be the process that favours the reproductive success of some individuals over others. Natural processes such as mutation and genetic drift provide the raw materials for evolution. Phenotype fitness to the environment determines the direction of evolution. The rate of environmental change determines the rate of evolution.
Natural selection depends on the following:
1) genetic variation exists to provide multiple alleles for individual traits and/or different combinations of alleles are present across a population
2) overpopulation of diverse offspring (reproductive cycles)
3) competition for survival
4) differential reproductive success
Artificial Selection on the other hand is about managing sexual reproduction. It involves humans deciding which organisms are chosen or permitted to reproduce. Farmers have been doing this for centuries in an effort to increase yield (get more food from less plants and animals - such as larger fruit, faster growing animals, etc.) and cull negative traits/disease from populations by preventing some animals from breeding.
It is important to remember that selective breeding still depends on mutations appearing in populations naturally. Often cross-breeding can be used to improve the combinations of alleles in a population and even create new hybrid breeds or varieties. Developing pure breeding (homozygous) populations usually involves inbreeding which causes a reduction in genetic variation. This can sometimes increase the chance of otherwise rare recessive conditions becoming more common. Out breeding can increase genetic variation when inbreeding leaves a population with reduced variation.
Selective Breeding Techniques:
1) Phenotype Inspection (Select and cull)
2) Gamete Analysis
3) Genetic screening
4) In vitro fertilisation (IVF) and embryo transfer
ANIMAL PHARM
This introductory video produced by the BBC provides food for thought around biotechnology and begs the question, "just because we can, should we?"
In this documentary series Scientist Olivia Judson and food
journalist Giles Coren share their journey into Genetic Modification and Genetic Engineering as scientists explore the use of biotechnology to overcome limitations of "traditional" approaches to food production and medicine.
Belgian Blue Cows
1) Describe the natural process responsible for the
Belgian Blue phenotype.
2) Explain the process involved in accentuating the
original phenotype to make today’s Belgian Blue variety (one tonne)
3) How does the meat from these cows compare to
“regular” beef?
4) Which gene is affected in these cows?
5) How do they use technology to analyse the
quality of males before choosing which ones will be allowed to reproduce?
Fruit and Vegetables
6) How and why have carrots been genetically
modified?
7) List three other foods that have been modified
for our eating by farmers through selective breeding.
Scaleless Chicken
1) Chickens have been bred to grow as fat and fast
as possible. They have a fast heart rate and high metabolism. What problem does
this pose for chickens and chicken farmers
2) What does Dr Avigdor Cahaner want to do to solve
the problem. Instead of...
3) Why is the featherless mutation called
‘scaleless’?
4) Why do the featherless chickens look so red?
5) The original mutation took place in small
chickens. How did Dr Avigdor get larger featherless chickens (how many
generations?)?
6) What do these chickens have in common with pigs?
7) Opinions: Write a short response to discuss the
advantages and disadvantages of selective breeding cows and chickens. Consider
the perspective of the cows, the chickens and the farmers.
Transgenesis
Rabbits
1) What does the word transgenesis mean?
2) Explain how Dr Houdebine got rabbits to glow
green (draw a labelled diagram)?
3) What advantages do you think transgenesis has
over selective breeding?
4) What does scientist Olivia Judson find so
amazing about the glowing rabbits
5) OPINION: write a short paragraph to express your
thoughts on this technology. Can you think of any uses for it?
In the episode of Animal Pharm, the process of moving the green fluorescent protein (GFP) gene from jellyfish to rabbits is introduced. This process relies on a couple universal truths about DNA.
DNA is the universal code for life on Earth
DNA codes for proteins
Cells with the machinery to produce proteins can express the mRNA of from genes of other species
Developing this technology came from observing DNA replication and understanding how bacteria and viruses infecting cells.
Historic Discoveries:
1) RNA viruses such as herpes virus and HIV produce an enzyme inside cells called reverse transcriptase that turns their single stranded RNA into double stranded DNA.
2) DNA ligase joins adjacent Okazaki fragments on the lagging strand of DNA
3) restriction enzymes in bacteria help cut circular DNA strands at specific recognition sites (base sequences) permitting genetic recombination
4) bacteria living in thermal vents (in New Zealand) have enzymes to allow for DNA replication at high temperatures (they don't denature).
There are several ways to transfer a gene from one organism to another. The basic steps in transgenesis include:
1) Identifying the gene sequence or sequences responsible for the desired phenotype
From your knowledge of transcription and translation, you would know that any cell expressing a gene will have a MRNA copy of the gene in the cytoplasm. Scientists can use this knowledge to determine the gene sequences responsible for the trait.
2) Isolating a gene of interest
Using the enzyme reverse transcriptase, we can use single stranded RNA to produce a double stranded cDNA copy of the gene (without tricky introns). Enzymes can also be used to cut long chromosomes to find a shorter segment of DNA that can then be used in PCR.
3) Amplifying the gene (making many copies)
Polymerase Chain Reaction is a process that uses our knowledge of DNA replication to replicate a specific gene in vitro. Before watching the video on PCR, here is a video to remind you of the DNA replication process.
Polymerase Chain Reaction (PCR)
PCR is the first step in making many copies of DNA from a small and even limited sample of tissue. It is an invitro method of amplifying specific DNA sequences targeted by primers. Heat denaturing of DNA, Taq polymerase and automated thermocycling are key steps of PCR.
Alternatively, genes can be inserted into bacterial plasmids, then when bacteria transfected with the plasmids reproduce they copy the gene of interest. (see video below transfection)
4) Transfection (moving the gene into the target species)
- Gene guns can directly fire gene sequences into cells. This can be destructive and limited primarily to use with plants.
- Nuclear injection using a micropipette can inject cells directly under a microscope.
- Electroporation uses electrical impulses to assist genes to enter cells.
- Bacteria (Agrobacterium) can transfect plant embryos.
Have a look at this video which uses bacteria to transfect plants with new genes.
Before you watch it, the technique involved replacing tumour causing genes from a bacteria plasmid with a gene that scientists want plants to get. (it gets a bit complicated around 7 - 8 min) Rather than the transfer of DNA causing tumours in the plant, the plant gets a new gene!
Examples of using these techniques:
Selective Breeding/polyploidy in Bread Wheat -
History of wheat: The picture below shows the history of bread wheat. It explains how wild grass varieties cross pollinated one another and produced hybrid species. Natural processes and selective breeding have resulted in today's common bread wheat.
Watch the video below to explore ideas related to modern selective breeding techniques to enhance what mother nature has already provided. Questions below the video will focus your attention on some of the key ideas.
Questions:
1) What plants are scientists looking to cross with bread wheat?
2) What are they attempting to achieve?
3) Explain how they use conventional crossing to know where the DNA came from for each of the new plants (plant reproduction revision)
4) The seeds they produce have a problem. Scientists use a chemical called colchicine. What does this chemical do?
5) When looking at new plants, what traits are they looking to select for? What challenges are they trying to solve (food security and climate change?
In this video Pamela Ronald looks at how GE technology can be used to combat food poverty created by climate change. It highlight how genes are discovered and how scientists test their hypothesis.
Questions:
1) Pamela (geneticist) and her husband (organic farmer) have the same goal, what is it?
2) What % of rice crops are lost to pests and disease?
3) What environmental problem do rice farmers face (increasing with climate change)?
4) How long did it take scientists to discover the SUB1 gene for flooding resistance?
5) How much more grain can be harvested using the SUB1 rice following flooding?
6) It is estimated that 300 000 people die every year due to exposure to harmful chemicals in agriculture. What are scientists doing to combat this?
7) What vitamin deficiency and condition are scientists trying to combat by making golden rice?
8) Pamela mentions that some people argue against GMOs what are some of the reasons provided in the final interview?
CLONING BY
SOMATIC CELL NUCLEAR TRANSFER
One technique used in science is somatic cell nuclear transfer. This process involves first obtaining two cells; one egg cell and one somatic diploid cell. By removing the nucleus from the harvested egg, a cell containing all the machinery necessary to support the development of a zygote is prepared. Next, the nucleus from a diploid cell is implanted into the enucleated egg cell. Placed in the appropriate growth medium under the right conditions, the diploid cell created is stimulated to start its development into an embryo by rapidly dividing by mitosis.
The primary application of Somatic Cell Nuclear Transfer is based in agriculture, where the advantage of producing high numbers of phenotypically desirable offspring is met with high economic returns. Cloning was developed to sidestep meiosis where chance events such as segregation, independent assortment, and recombination during sexual reproduction may risk to interfere with fitness, productivity and overall profiitabilty of offspring.
Gene Editing using CRISPR
When people refer to Crispr, they're probably
talking about Crispr-Cas9, a complex of enzymes and genetic guides that
together finds and edits DNA. But Crispr on its own just stands for Clustered
Regularly Interspaced Palindromic Repeats—chunks of regularly recurring bits of
DNA that arose as an ancient bacterial defense system against viral invasions.
Viruses work by taking over a cell, using its machinery
to replicate until it bursts. So certain bacteria evolved a way to fight back.
They deployed waves of DNA-cutting proteins to chop up any viral genes floating
around. If the bacteria survived the attacks, they'd incorporate tiny snippets
of virus DNA into their own genomes—like a mug shot of every foe they’d ever
come across, so they could spot each one quicker in the future. To keep their
genetic memory palace in order, they spaced out each bit of viral code
(so-called “guide RNAs”) with those repetitive, palindromic sequences in
between. It doesn't really matter that they read the same forward and backward;
the important thing is that they helped file away genetic code from viral
invaders past, far away from more essential genes.
And having them on file meant that the next time a
virus returned, the bacteria could send out a more powerful weapon. They could
equip Cas9—a lumpy, clam-shaped DNA-cutting protein—with a copy of that guide
RNA, pulled straight out of storage. Like a molecular assassin, it would go out
and snip anything that matched the genetic mug shot.
Check out this first video which animates the technique:
To understand a bit more about CRISPR technology, this video explores some applications, discussing possible targets for gene editing. In particular it discusses how gene drives amplify the effectiveness of CRISPR in manipulating genomes.
This video explores further the strategy to eliminate malaria using CRISPR. Can you think of implications for mosquitoes, humans, and other organisms in the environment:
- Health and survival of populations
- Biodiversity
- Ecosystems
- Evolution of populations
Additional Techniques: under development
Gel Electrophoresis
Agarose gel electrophoresis uses electric current to run different length samples of DNA through a gel obstacle course. Run along side a sample of DNA fragments of known length (reference ladder) unknown sample lengths may be identified. Furthermore, for the purpose of profiling, the banding patterns from one unknown DNA sample and several known samples can be compared to see relatedness.
GENE CHIP TECHNOLOGY
Click on the following link to explore an animation demonstrates how to tell the differences in genes being expressed by two different cells. This has powerful applications particularly in understanding which genes may be responsible for causing certain illnesses.
