Biology IB HL - 3.5 Genetic Modification Part 2

DNA ligase joins the vector and gene by fusing their sugar-phosphate backbones together with a covalent phosphodiester bond

The recombinant construct (including the gene of interest) is finally introduced into an appropriate host cell or organism

This process can be achieved in a variety of ways and is called transfection (for eukaryotes) or transformation (for prokaryotes)

Antibiotic selection is commonly used in order to identify which cells have successfully incorporated the recombinant construct

The plasmid vector contains an antibiotic resistance gene, so only transgenic cells will grow in the presence of antibiotic

Transgenic cells, once isolated and purified, will hopefully begin expressing the desired trait encoded by the gene of interest

Genetically modified organisms (GMOs) are used in agriculture to improve crop yields and reduce farming costs

However the use of GM crops is a contentious issue, as economic benefits must be weighed against environmental risks

GM crops can be used to improve human nutritional standards, by incorporating genes for certain proteins, vitamin or vaccines

Additionally, GM crops can be manufactured that lack common natural allergens or toxins

However, the inclusion or removal of certain genes could trigger unexpected adverse health reactions in some individuals

Currently, not all foods with GM components are labelled, making informed decisions of use difficult for consumers

GM crops can include genes to enable them to grow in a wider range of environments (e.g. drought / frost / salinity resistance)

GM crops can be manufactured to produce greater yields (crops can potentially grow larger and faster)

GM crops can include genes which slow the rate of spoiling, leading to longer shelf lives for GM foods

GM crops may possess resistance to certain viruses or produce toxins to pests (reducing need for the use of pesticides)

Herbicide resistant crops can be used to allow for the easier killing of weeds (which compete with crops for soil nutrients)

Overall, an improved yield, reduction in farming costs and ability to farm more land will provide an economic benefit to farmers

However, patent protection allows biotech companies to restrict the use of seeds and force farmers to pay high prices for use

The ability to farm a wider range of environments with GM crops will potentially reduce the need for associated deforestation

However, GM crops could potentially reduce biodiversity in a region by competing with indigenous plant life

Furthermore, proteins or toxins produced by GM crops could negatively affect certain organisms within the ecosystem

Cross-pollination by GM crops could also result in the formation of herbicide-resistant weeds and grasses

GM crops with pest toxins could also accelerate the evolution of resistant pest species

Also, the generation of pest-resistant crops means that less chemical insecticides will be released into the environment

t corn is a genetically modified maize that incorporates an insecticide producing gene from the bacterium Bacillus thuringiensis

This insecticide is lethal to certain types of larvae, particularly the European corn borer which would otherwise eat the crop

Concerns have been raised that the spread of Bt corn may also be impacting the survival rates of monarch butterflies

While monarch butterfly larva feed exclusively on milkweed, wind-borne pollen from Bt corn may dust nearby milkweeds

Monarch caterpillars were fed milkweed leaves that had been dusted with pollen from Bt corn (to simulate spread via wind)

Growth and mortality rates were compared against caterpillars fed on non-dusted leaves or leaves dusted with non-GM pollen

Caterpillars exposed to Bt pollen were found to have eaten less, grew more slowly and exhibited higher mortality rates

Some scientists suggested that these results may lack validity as they do not accurately reflect natural conditions

There were higher amounts of Bt pollen on the leaves than would be found naturally (e.g. rain would diminish build up)

Larva were restricted in their diet (in the field, larva could feasibly avoid eating pollen dusted leaves)

A second study was conducted comparing the survivor rates of monarch butterflies based on proximity to Bt corn fields

There was no significant increase in mortality when monarch larva were placed in or near an actual Bt corn field

From this it was concluded that exposure to Bt pollen poses no significant risk to monarch butterfly populations

Clones are groups of genetically identical organisms or a group of cells derived from a single original parent cell

Organisms that reproduce asexually will produce genetically identical clones

YES

Additionally, mechanisms exist whereby sexually reproducing organisms can produce clones (e.g. identical twins)

Cloning multicellular organisms requires the production of stem cells (differentiated cells cannot form other cell types)

Stem cells can be artificially generated from adult tissue using a process called somatic cell nuclear transfer (SCNT)

Somatic cell nuclear transfer is a method by which cloned embryos can be produced using differentiated adult cells

Somatic cells are removed from the adult donor and cultured (these cells are diploid and contain the entire genome)

An unfertilised egg is removed from a female adult and its haploid nucleus is removed to produce an enucleated egg cell

The enucleated egg cell is fused with the nucleus from the adult donor to make a diploid egg cell (with the donor’s DNA)

An electric current is then delivered to stimulate the egg to divide and develop into an embryo

The embryo is then implanted into the uterus of a surrogate and will develop into a genetic clone of the adult donor

YES

Many species can reproduce asexually and hence possess natural methods of cloning

All bacteria, the majority of fungi and many species of protists reproduce asexually to produce genetic clones

While most plants reproduce sexually, they also possess methods of asexual reproduction (vegetative propagation)

Certain animal species can also reproduce asexually, via a variety of different mechanisms

binary fission

budding

fragmentation

parthenogenesis

The parent organism divides equally in two, so as to produce two genetically identical daughter organisms

This method of cloning occurs in Planaria (flatworms) but is also common to bacteria and protists (e.g. euglena, amoeba)

Cells split off the parent organism, generating a smaller daughter organism which eventually separates from the parent

This method of cloning occurs in Hydra but is also common to many species of yeast

New organisms grow from a separated fragment of the parent organism

This method of cloning is common to starfish and certain species of annelid worms

Embryos are formed from unfertilised ova (via the production of a diploid egg cells by the female)

This method of cloning occurs in certain species of insect, fish, amphibians and reptiles

Plants have the capacity for vegetative propagation, whereby small pieces can be induced to grow independently

This is because adult plants possess meristematic tissue capable of cellular differentiation (totipotent)