Variation & Evolution Flashcards
All 30 cards in this deck
What is variation?
Differences in the characteristics (phenotypes) of individuals of the same species, caused by genes, the environment, or a combination of both. There is usually extensive genetic variation within a population.
How do the genome and the environment together produce an organism's phenotype?
e.g. the height of a tomato plant
The genome sets which characteristics can develop, and the environment affects how they actually develop.
e.g. genes set the possible height, but light, water and minerals decide the actual height.
True or false? Two genetically identical plants grown in the same garden must grow to the same height.
False. Environmental differences (light, water, minerals, soil pH, disease, herbivores) change the phenotype.
What is a mutation?
A change in the DNA (base sequence), which may change a gene or allele.
What effect do mutations have on the phenotype?
Most have no effect on the phenotype, some influence it, and very rarely a mutation leads to a new phenotype. Mutations occur continuously.
When can a single mutation lead to a relatively rapid change in a species?
When the new phenotype it produces is suited to an environmental change.
What is evolution?
A change in the inherited characteristics of a population over time, through the process of natural selection, which may result in the formation of a new species.
What does the theory of evolution by natural selection state about the origin of species?
All species of living things have evolved from simple life forms that first developed more than three billion years ago.
What are the steps to explain a characteristic by natural selection?
e.g. rabbits living where the climate becomes colder
- Variation: some rabbits have thicker fur than others.
- Those better adapted survive and reproduce: thick-furred rabbits survive the cold and breed.
- The favourable alleles are passed on: thick fur becomes more common in the population.
When have two populations of one species become two new species?
When their phenotypes are so different that they can no longer interbreed to produce fertile offspring.
True or false? An individual organism evolves during its lifetime to become better adapted.
False. Individuals cannot evolve; populations change over many generations as favourable alleles become more common.
What is selective breeding (artificial selection)?
The process by which humans breed plants and animals for particular genetic characteristics.
What are the steps of selective breeding?
e.g. breeding cows for a high milk yield
- Choose parents with the desired characteristic from a mixed population: cows with the highest milk yield.
- Breed them together and select the offspring showing the characteristic most: the calves giving most milk.
- Breed these offspring together, repeating over many generations until all offspring show it.
Give three characteristics that plants and animals are selectively bred for.
Disease resistance in food crops, larger or more unusual flowers, animals that produce more meat or milk, and domestic dogs with a gentle nature.
What is the problem of inbreeding caused by selective breeding?
Some breeds become particularly prone to disease or to inherited defects, because the gene pool is reduced.
True or false? Selective breeding increases the genetic variation in a population.
False. It reduces variation (a smaller gene pool), which can leave a breed vulnerable to disease or new conditions.
In a breeding programme, the mean mass of fruit rises over ten successive generations. What does this show?
That large fruit mass is being selected for and passed on to offspring, so the selective breeding is working.
What is genetic engineering?
A process in which the genome of an organism is modified by introducing a gene from another organism to give a desired characteristic.
Give one use of genetic engineering in medicine.
Bacterial cells are genetically engineered to produce useful substances such as human insulin to treat diabetes.
What are GM crops, and what characteristics are they given?
Crops whose genes have been modified by genetic engineering; examples are resistance to insect attack or to herbicides. GM crops generally show increased yields.
What are the main steps in the process of genetic engineering?
e.g. making bacteria that produce human insulin
- Enzymes are used to isolate the required gene: the human insulin gene.
- The gene is inserted into a vector, usually a bacterial plasmid or a virus.
- The vector puts the gene into the cells of the other organism: the bacteria then make human insulin.
What is a vector in genetic engineering?
Something used to carry the required gene into the cells of another organism - usually a bacterial plasmid or a virus.
Give two concerns people have about GM crops.
The effect on populations of wild flowers and insects (reduced biodiversity), and that the effects of eating GM crops on human health have not been fully explored. The inserted gene may also transfer to wild plants.
What is tissue culture as a method of cloning plants?
Using small groups of cells from part of a plant, grown to produce identical new plants. It is used to preserve rare plant species and commercially in nurseries.
What are cuttings as a method of cloning plants?
An older, simple method where gardeners take pieces of a parent plant and grow them into many identical new plants.
What are the steps of cloning by embryo transplant?
e.g. cloning a prize cow
- Cells are split apart from a developing animal embryo before they become specialised.
- Each identical embryo is transplanted into a host mother.
- The host mothers give birth to calves genetically identical to each other.
What are the steps of adult cell cloning?
e.g. cloning an adult sheep
- The nucleus is removed from an unfertilised egg cell.
- The nucleus from an adult body cell, such as a skin cell, is inserted into the egg cell.
- An electric shock makes it divide into an embryo, which is inserted into the womb of an adult female: the lamb is a clone of the skin cell donor.
Give one benefit of cloning plants or animals.
Many organisms with the desired characteristics can be produced quickly and they are all genetically identical; it can also preserve rare species.
True or false? Cloning increases the genetic variation of a population.
False. Clones are genetically identical, so the gene pool is reduced and the whole population could be wiped out by one disease or environmental change.
True or false? There is usually extensive genetic variation within a population of a species.
True. Mutations occur continuously, so members of a species differ widely in their alleles.