Variation, evolution and genetic technologies

Biology · Inheritance, variation and evolution. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

Variation between individuals comes from their genes, their environment, or both. New alleles appear by mutation. In natural selection, individuals with the characteristics best suited to the environment are more likely to survive and breed, so they pass on their alleles. Over many generations the useful characteristic becomes more common.

In selective breeding, humans choose the parents. In genetic engineering, a gene from one organism is cut out and put into the genome of another to give a desired characteristic.

Clones are genetically identical individuals. They can be made from plants by cuttings or tissue culture, and from animals by embryo transplants or adult cell cloning.

Rules to remember

Natural selection: variation → competition → the best suited survive and breed → their alleles are passed on.
A new species has formed when two populations can no longer interbreed to produce fertile offspring.
Selective breeding: choose parents with the desired characteristic, breed them, choose the best offspring, repeat for many generations.
Risk of selective breeding: inbreeding, which makes some breeds prone to disease or inherited defects.
Genetic engineering: enzymes cut out the gene → it is inserted into a vector (a bacterial plasmid or a virus) → the vector puts the gene into the target cells at an early stage of development.
GM crops can resist insects or herbicides and give higher yields. Concerns: effects on wild flowers and insects, and possible effects on human health that are not fully studied.
Adult cell cloning: the nucleus of an adult body cell is put into an egg cell that has had its nucleus removed; an electric shock makes it divide; the embryo is put into a female's womb.

Common mistake

Do not write that organisms change because they need to. Individuals do not adapt during their lives; the variation is already there by mutation and the environment selects it.

Worked example

Scientists want a maize plant that makes a bacterial protein which kills the insects that eat it. Put the main steps of the genetic engineering in order.

Enzymes are used to cut the gene for the protein out of the bacterial DNA.
The gene is inserted into a vector, such as a plasmid or a virus.
The vector carries the gene into maize cells at a very early stage of development.
The plant grows with the gene in its cells and makes the protein.

Answer: Cut out the gene → put it in a vector → transfer it to early maize cells → the plant develops with the new characteristic.

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Inheritance Variation And Evolution — Worksheet

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