Selective breeding and genetic modification

Selective breeding

Plants & Animals

• Selective breeding means to select individuals with the characteristics you want and breed them together

• The process doesn’t stop there though because it’s likely that not all of the offspring will show the characteristics you want so offspring that do show the desired characteristics are selected and bred together

• This process has to be repeated for many successive generations before you can definitely say you have a ‘new breed’ which will reliably show those selected characteristics in all offspring

Plants are selectively bred for development of many characteristics:

• disease resistance in food crops 

• increased crop yield

• hardiness to weather conditions

• better tasting fruits large or unusual flowers

• An example of a plant that has been selectively bred in multiple ways is wild brassica, which has given rise to cauliflower, cabbage, broccoli, brussel sprouts, kale and kohlrabi

Animals

• Selective breeding of animals has been carried out by humans for thousands of years

• It takes place in the same way as selective breeding of plants Individuals with the characteristics you want are bred together (often several different parents all with the desired characteristics are chosen so siblings do not have to be bred together in the next generation)

• Offspring that show the desired characteristics are selected and bred together

• This process is repeated for many successive generations before you can definitely say you have a ‘new breed’ which will reliably show those selected characteristics in all offspring

Animals are commonly selectively bred for various characteristics, including:

• Farm animals that produce lots of milk or meat

• chickens that lay large eggs

• domestic dogs that have a gentle nature

• sheep with good quality wool

• horses with fine features and a very fast pace

• chickens that lay large eggs

• An example of an animal that has been selectively bred by humans in many ways to produce breeds with many different characteristics is the domestic dog, all breeds of which are descended from wolves

Open Ended

Explain the term 'selective breeding'

Open Ended

Give 3 reasons why plants would be bred selectively

Open Ended

Give 4 reasons why animals are selectively bred

Open Ended

Give two ways in which selective breeding is different from natural selection

Genetic modification

Making Recombinant DNA

• Genetic engineering is changing the traits of one organism by inserting genetic material from another organism

• The organism receiving the genetic material is said to be ‘genetically modified’

• The DNA of the organism that now contains DNA from another organism as well is known as ‘recombinant DNA’

The process

• The gene that is to be inserted is located in the original organism (for example, this could be the gene for human insulin)

• Restriction enzymes are used to isolate the required gene, leaving it with ‘sticky ends’ (a short section of unpaired bases)

• A vector, which is usually a bacterial plasmid or a virus, is cut by the same restriction enzyme leaving it with corresponding sticky ends

• The vector and the isolated gene are joined together by ligase enzymes

• If two pieces of DNA have matching sticky ends (because they have been cut by the same restriction enzyme), ligase will link them to form a single, unbroken molecule of DNA

Vectors for Recombinant DNA

• A vector is a vehicle to artificially carry foreign genetic material into another cell, where it can be replicated and/or expressed

• The two main types of vectors are bacterial plasmids and viruses

• Plasmids are circles of DNA that are found in bacteria

• When the bacteria reproduce the plasmids are copied as well and so a recombinant plasmid can quickly be spread as the bacteria multiply and they will then all express the gene

• Viruses will carry recombinant DNA and infect organisms that they come into contact with, making the host organism express the recombinant DNA

Manufacture of Insulin

• Insulin is needed in large quantities to help treat diabetes

• Prior to the development of genetic engineering, insulin for human use was collected from pigs

• Bacteria are now genetically engineered to produce human insulin which can be collected and purified for use with no fear of rejection

Improving food production

• Genetically modified plants are plants that have had foreign DNA inserted into their genome Tomatoes have been modified to make them grow larger

• Wild rice has been genetically modified to produce beta carotene 

• Crop plants have been genetically modified to be resistant to herbicides

Transgenic Organisms

• The term ‘transgenic’ means the transfer of genetic material from one species to a different species

• This means that a transgenic organism contains genes from a different species

• For example, the recombinant bacteria used to  produce human insulin are transgenic as they contain genetic material from a human

Fill in the Blanks

Open Ended

Describe the effect of growth hormone on milk production

Open Ended

Describe how growth hormone could be destroyed in the stomach

Multiple Choice

The term that best describes bacteria that have genetically modified to produce human insulin is

• Antibiotic

• Aseptic

• Pathogenic

• Transgenic

Multiple Choice

Name the enzyme that cuts DNA

• Restriction

• Ligase

• Vector

Multiple Choice

Name the enzyme that joins DNA

• Restriction

• Ligase

• Vector