Topic 6b - Variation and Evolution Flashcards
What is variation?
Variation is defined as differences between individuals of the same species.
What is phenotypic variation?
Phenotypic variation is the difference in features between individuals of the same species.
What can phenotypic variation be caused by? (3)
- It can be genetic – controlled entirely by genes (this is called genetic variation).
- It can be environmental – caused entirely by the environment in which the organism lives.
- Or it can be due to a combination of genes and the environment.
What are some examples of genetic variation in humans? (5)
- blood group
- eye colour
- sex
- ability to roll tongue
- free or fixed earlobes
What environmental factors can characteristics of all species be affected by? (5)
- climate
- diet
- accidents
- culture
- lifestyle
What are some examples of environmental variation? (4)
- An accident may lead to scarring on the body.
- Eating too much and not leading an active lifestyle will cause weight gain.
- Being raised in a certain country will cause you to speak a certain language with a certain accent.
- A plant in the shade of a big tree will grow taller to reach more light.
What is an example of features affected by genetic and environmental variation? (4 bullet points)
- Tall parents will pass genes to their children for height.
- Their children have the genetic potential to also be tall
- However, if their diet is poor then they will not grow very well.
- Therefore their environment also has an impact on their height.
What is a summarised way of viewing how genetic and environmental variation can work together?
Although genes decide what characteristics we inherit, the surrounding environment will affect how these inherited characteristics develop.
Where do all genetic variants arise from?
Mutations
Do most mutations have an impact on the phenotype? Why?
Most mutations have no effect on the phenotype as the protein that a mutated gene produces may work just as well as the protein from the non-mutated gene.
How can mutations lead to a relatively rapid change in a species? (3)
- Rarely, mutations lead to the development of new alleles and so new phenotypes and if they do, most only have a small effect on the organism.
- Occasionally, the new allele gives the individual a survival advantage over other members of the species.
- If the new phenotype is suited to an environmental change it can lead to a relatively rapid change in the species.
What is evolution?
A change in the inherited characteristics of a population over time.
How does evolution occur?
By natural selection
How does evolution occur by natural selection?
During natural selection individuals with phenotypes that are best suited to their environment are more likely to survive and pass on their features to their offspring.
What does the theory of evolution by natural selection state?
The theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago.
What can natural selection lead to the development of?
Natural selection can lead to the development of new species by a process known as speciation.
What is speciation/ when is it said to have occurred?
Speciation is said to have occurred when two populations have phenotypes that are so different that they can no longer breed together to produce fertile offspring.
What is selective breeding? (2 bullet points)
- Selective breeding means to select individuals with desirable characteristics/particular genetic characteristics 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.
Why does selective breeding have to be repeated?
The 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.
How long have humans been using selective breeding?
Humans have been doing this for thousands of years since they first bred food crops from wild plants and domesticated animals.
How has selective breeding helped humans?
This has helped the human population to grow by providing increased yields (and increased quality) of plant products and animals products.
What are some examples that animals are selectively bred for? (5)
- cows, goats and sheep 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
What is an example of an animal that has been selectively bred by humans in many ways?
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.
What are some examples that plants are selectively bred for? (5)
- disease resistance in food crops
- increased crop yield
- hardiness to weather conditions (eg. drought tolerance)
- better tasting fruits
- large or unusual flowers
What is an example of a plant that has been selectively bred by humans in many ways?
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 kohlrab.
What is the main problem with selective breeding? (2 bullet points)
- Selective breeding can lead to ‘inbreeding’.
- This occurs when only the ‘best’ animals or plants (which are closely related to each other) are bred together.
What does inbreeding result in?
It results in a reduction in the gene pool – this is a reduction in the number of alleles (different versions of genes) in a population.
What does inbreeding and the resultant reduction in the gene pool increase the chance of? (2)
- organisms inheriting harmful genetic defects
- organisms being vulnerable to new diseases (there is less chance of resistant alleles being present in the reduced gene pool)
What is genetic engineering?
Genetic engineering is changing the genetic material of an organism by removing or altering genes within that organism, or by inserting genes from another organism.
What is the organism receiving genetic material in genetic engineering said to be?
The organism receiving the genetic material is said to be ‘genetically modified’, or is described as a ‘transgenic organism’.
What is the DNA of the organism that now contains DNA from another organism in genetic engineering known as?
The DNA of the organism that now contains DNA from another organism as well is known as ‘recombinant DNA’
What are genetically modified crops (GM crops)?
Genetically modified crops are plants that have had foreign DNA inserted into their genome.
Why are plants genetically engineered?
It is usually done to improve food production in some way.
What are some examples of genetically modified crops? (3)
- Tomatoes have been genetically modified to make them grow larger fruit.
- Wild rice has been genetically modified to produce beta carotene (needed by humans to make vitamin A).
- Crop plants have been genetically modified to be resistant to diseases or resistant to certain herbicides.
What is the process of using bacteria in genetic engineering to produce human proteins, e.g. insulin? (9) - blurting / whiteboard
- The human gene / DNA that codes for human protein (i.e. insulin) is identified.
- The gene is removed using restriction enzymes.
- This will form complimentary / sticky ends.
- A plasmid is cut using the same restriction enzyme.
- The human gene is inserted into the plasmid.
- DNA ligase is used to join the gene with the plasmid.
- The recombinant plasmids are inserted into bacteria.
- Bacteria with recombinant plasmids asexually reproduce.
- The genetically engineered bacteria can be identified / purified and placed in a fermenter to reproduce quickly in controlled conditions and make large quantities of the human protein (i.e. insulin).
What is a simpler version of the process of genetic engineering? (5) - blurting / whiteboard
- Enzymes are used to isolate (cut out) the required gene.
- This gene is inserted into a vector.
- The vector is usually a bacterial plasmid (a piece of circular DNA found inside bacterial cells) or a virus.
- The vector is used to insert the gene into the required cells of the target organism.
- Genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics.
What is golden rice - example of a GM crop?
Golden rice contains genes from another plant and a bacterium which make the rice grains produce a chemical that is turned into vitamin A in the human body, which could help prevent deficiency diseases in certain areas of the world.
What are the concerns about GM crops?
Concerns about GM crops include the effect on populations of wildflowers and insects. Some people feel the effects of eating GM crops on human health have not been fully explored.
What is gene therapy in terms of genetic engineering - curing diseases? (3)
- Modern medical research is exploring the possibility of genetic modification to overcome some inherited disorders.
- As these inherited genetic diseases are caused by faulty genes, it may be possible to treat these by inserting working versions of these genes into people with the genetic disease.
- This is called gene therapy.
What is tissue culture?
Tissue culture is a process in which very small pieces of plants (‘tissue’) are grown (‘cultured’) using nutrient media.
What does in vitro mean?
outside a living organism
What is plant propagation?
Plant propagation is the production of new plants naturally or by artificial methods.
How do you propagate plants in vitro - tissue culture? (4)
- Cells are scraped from the parent plant (these cells are known as explants).
- The cells are transferred to a sterile petri dish containing nutrient agar.
- Hormones (eg. auxins) are added to encourage plants to grow into small masses of tissue (callus tissue).
- Tissue continues to grow and forms plantlets that can be transferred to individual potting trays and develop into plants.
What is a clone?
Clones are genetically identical individuals.
What kind of uses does plant cloning have?
Commercial uses
How does tissue culture allow plants with desirable characteristics to be grown? (4)
- cheaply
- with a greater yield (a large number of plants can be produced)
- quickly
- at any time of the year
What can tissue culture ensure the prevention of?
It can also ensure diseases prevalent in other areas of the world are not imported and spread by ensuring native varieties of plants are produced in large enough quantities to supply demand in one country without importing plants from abroad.
What can tissue culture be important in preserving?
Tissue culture can also be an important process in preserving rare plant species.
What is an older and simpler method to clone plants?
By taking cuttings
How does taking cuttings work as a method of cloning? (2)
- Gardeners take cuttings from good parent plants (eg. those that are healthiest and best-looking) – a section of the parent plant with a new bud is cut off.
- These cuttings are then planted and grow into genetically identical versions of the original plant.
How can plants cloned by taking cuttings be produced?
quickly and cheaply
How does the process of embryo cloning work using the example of cattle?
- Egg cells from the best cow are artificially fertilised using sperm cells taken from the best bull.
- This forms a zygote which develops into an embryo and is then removed from the uterus.
- The developing animal embryo is then split apart many times before the cells of the embryo become specialised.
- This forms many separate embryos that are genetically identical.
- These cloned embryos are then transplanted into host mothers.
- The calves born from these host mothers are all genetically identical => clones of best cattle.
How is adult cell cloning achieved?
- 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.
- A very small electric shock stimulates the egg cell to divide (by mitosis) to form an embryo.
- These embryo cells contain the same genetic information as the adult skin cell.
- When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female (known as the surrogate mother) to continue its development until birth.
What is the first successful use of adult cell cloning? (3)
- Adult cell cloning was used to create the first clone (exact genetic copy) of a mammal in 1996.
- Scientists in Scotland successfully cloned an adult female sheep.
- The clone was called Dolly.
What are the benefits of cloning? (3)
- Cloning could be used to help preserve endangered species of plants and animals.
- Cloning makes it possible to quickly and cheaply produce commercial quantities of consistently high quality plants at any time of the year.
- Cloning allows farmers to ensure consistently high quality livestock.
What are the risks of cloning? (3)
- Cloning can result in a reduced gene pool (similarly to selective breeding). This means there are fewer different alleles in a population, leaving the population with a smaller chance of having resistance to new diseases.
- There is some evidence that cloned animals may not be as healthy as normal ones.
- Some people worry that humans might be cloned in the future. This is considered deeply unethical by the vast majority of people. In addition, early attempts might be unsuccessful (eg, they could result in children born with severe disabilities).
