Revision notes. Reproduction and Variation - genes, reproduction and genetic engineering.

Sexual reproduction

• Sexual reproduction - the joining (fusion) of male and female gametes.
• The mixture of the genetic information from two parents leads to variety in the offspring.
• Genes are passed on in the sex cells (gametes) from which the offspring develop.

The causes of variation

• Sexual reproduction - leads to variety in the offspring
• Asexual reproduction - no variation in the offspring.

Individuals within a species vary due to:

Genetic factors

• Meiosis – all gametes created by one person are genetically different.
• Random fertilisation
• Mutations

Environmental factors

• Nutrition
• Chemicals
• Temperature
• Light
• Physical forces

Cloning

• Humans can carry out various procedures to create clones of plants and animals.  
• These new individuals (clones) are genetically identical to the parents.

Cuttings:

• New plants can be produced quickly and cheaply by taking cuttings from older plants.

Tissue culture

• This uses small groups of cells from part of a plant to grow new plants.  
• They are grown in special growth media that provides all the essential nutrients and conditions for growth.

Embryo transplants

• This involves splitting apart cells from a developing animal embryo before they become specialised.
• The identical embryos are then implanted into the wombs of host mothers.

Fusion cell cloning

• This involves replacing the nucleus of an egg cell with the nucleus of an adult cell.  
• An electric shock is used to start the cell dividing to form an embryo.  
• This could be used to create stem cells to grow new tissues or organs.

Adult cell cloning

• This involves implanting an embryo formed by fusion cell cloning into the womb of a host mother, where it develops until it is born.  
• This could be used to clone animals with desired characteristics or even to save animals from extinction.

Concerns about cloning:

• People do not want human babies to be cloned.
• It produces lots of genetically identical individuals; they may struggle to survive if there is a change in the environment.

Genetic engineering

Genes from the chromosomes of humans and other organisms can be cut out using enzymes and transferred to cells of other organisms.

GM = Genetically modified

Examples of uses in food production:

• GM soya
• GM tomatoes
• Enzymes used to make vegetarian cheese

Examples of uses in medicine:

• Vaccine production
• Production of Factor VIII for haemophiliacs

Example in detail:  Insulin production for diabetics.

What is insulin?

• Hormone made in the pancreas
• Controls blood sugar levels
• Allows glucose to be stored as glycogen

What is diabetes?

• Condition where people cannot produce their own insulin
• This means they cannot control their blood sugar levels

Genetic engineering uses:

• Restriction enzymes – enzymes that ‘cut’ out sections of DNA
• Plasmids – circular pieces of DNA found in bacteria
• Bacteria – simple, unicellular organisms
• Ligase enzymes – enzyme that binds DNA together

The process:

• Cut out the insulin gene from the DNA of a human cell using an enzyme.
• Remove a ring of DNA (a plasmid) from a bacterium and open it up using the same enzyme.
• Insert the insulin gene into the plasmid using another enzyme.
• Enable a bacterium to take up the altered plasmid.
• Put the bacterium in a fermenter, and it multiplies many times.
• Each new bacterium contains the plasmid with the insulin gene.
• The bacteria produce insulin which can be extracted.

Other uses of genetic engineering

Genes can also be transferred to the cells of animals or plants at an early stage in their development so that they develop with desired characteristics:

• Gene therapy in could be used to insert healthy genes into foetuses that would otherwise develop a genetic disease.
• Genes can be inserted into clumps of plant cells, so that the adult plant can produce a chemical that kills pests.

Concerns about genetic engineering:

• Their may be long-term, unpredicted effects of consuming GM plants.
• Genes for pesticide resistance may spread form GM plants to their wild relatives, creating pesticide resistant weeds.
• People may want to manipulate the genes of their future children.
• Vegetarians may consume genes from animals if plants are genetically modified.