Variation and Evolution Flashcards
Describe what is Meant by Variation
Variation is all the differences in the characteristics of individuals in a population.
Explain how Genes Cause Genetic Variation
-All plants and animals have characteristics that are in some ways similar to their parent’s.
-This is because an organism’s characteristics are determined by the genes inherited from their parents.
-These genes are passed on in gametes from which the offspring develop. Most organisms get some genes from both parents.
-This combining of genes from two parents causes genetic variation- no two of the species are genetically identical.
-Some characteristics are determined only by genes. In animals these include: eye colour, blood group and inherited disorders.
Explain how a Species’ Environment Causes Variation
-The environment, including the conditions that organisms live and grow in, also causes differences between members of the same species- this is called environmental variation.
-For example, a plant grown in plenty of sunlight will be luscious and green but the same plant grown in darkness would grow tall and spindly and yellow leaves.
-Environmental variation covers a wide range of differences such as getting a suntan.
Explain how a Species’ Environment and Genes Cause Variation
-Most characteristics (e.g. weight, condition of teeth and height) are determined by a mixture of genetic and environmental factors.
-For example, some people have alleles which make them
likely to grow tall. However, their final height is also influenced by their diet which must contain enough calcium.
Describe how Mutations Can Introduce Variation
-Mutations are changes to the sequence of bases in DNA. They can lead to changes in the protein that a gene codes for.
-Most mutations have no effect on the protein the gene codes for, so most mutations have no effect on the organism’s phenotype.
-Some have a small influence on phenotype and so only alter characteristics slightly. However, although it is rare, mutations can result in a new phenotype being seen in a species.
-If the environment changes, and the new phenotype makes an individual more suited to the new environment, it can become common throughout the species relatively quickly by natural selection.
Describe what is Meant by Evolution
Evolution is the change in the inherited characteristics of a population over time through a process of natural selection.
Describe how an Animal Evolves from a Common Ancestor
-Isolation of different populations.
-Habitat variation between populations.
-Genetic variation or mutation (in each population).
-Better adapted survive and reproduce and pass on favourable alleles to offspring.
-Eventually they cannot produce fertile offspring with other populations
Explain how Rabbits Might Evolve to Suit a Colder Environment by Natural Selection
-Every rabbit has a slightly different combination of alleles to other rabbits. For example one rabbit may have alleles for thicker fur than other rabbits.
-In cold conditions the rabbits with alleles for thinner fur are less likely to survive. Rabbits with alleles for thicker fur are more likely to survive the cold conditions and reproduce.
-The rabbit’s offspring could inherit the alleles for thicker fur. These offspring are also more likely to survive and reproduce than rabbits with thinner fur.
-Over time, the alleles for thicker fur become more common than the alleles for thinner fur. This means that after many generations the rabbits will have thicker fur than before.
Explain how Rabbits Might Evolve to Survive a Predator in a Colder Environment by Natural Selection
-Foxes are a natural predator for rabbits. If snow is on the ground then rabbits with dark fur are likely to be seen by foxes and eaten.
-This means that the alleles for dark fur will not be passed on.
-However, rabbits with alleles for lighter fur are less likely to be seen by foxes and eaten. These rabbits are more likely to survive, reproduce and pass their alleles on to their offspring.
-Over time, the alleles for white fur become more common and the alleles for dark fur become less common.
Describe how Changes in a Phenotype can Cause Speciation
-Over a long period of time, the phenotype of organisms can change so much because of natural selection that a completely new species is formed.
-Speciation happens when populations of the same species change enough to become reproductively isolated- they can’t interbreed to produce fertile offspring.
Describe how Food Crops, Pet Dogs, Cattle and Garden Plants have Been Selectively Bred
Food crops - Crops have been selectively bred for resistance to disease.
Cattle such as cows - Cattle have been selectively bred for increased meat or milk.
Domestic dogs to be used as pets - Dogs have been selectively bred for a gentle nature.
Garden plants - These have been selectively bred to produce large or unusual flowers.
Describe the Stages in Selective Breeding
-From the existing stock, the farmer selects the ones which have the desired characteristic.
-The farmer will then breed them with each other.
-The farmer selects the offspring exhibiting the desired characteristic and allows them to breed.
-This process is repeated over several generations, until the traits are fully developed.
Explain why Breeding Closely related Organisms Can be a Problem
-When closely related organisms are bred together there is a risk of inbreeding.
-Inbreeding can lead to an increased risk of inherited diseases for example heart disease in dog breeds.
Describe the Advantages of Selective Breeding
-It can create new varieties of better crops. Characteristics may include higher yields and disease resistance.
-It can produce fitter and stronger animals. Characteristics may include higher yields, survival in harsh climates and disease resistance.
-This can lead to higher profits for farmers.
-Plants may also have shorter times before harvest.
Describe the Disadvantages of Selective Breeding
-Loss of genes in a population.
-Can lead to interbreeding which causes health problems and makes animals more susceptible to disease.
-This can cause animal discomfort and health problems.
Describe the Problems Caused by a Reduction in a Population’s Gene Pool
-During selective breeding, the farmer chooses from the ‘best’ animals are plants- which are closely related. This is inbreeding.
-Inbreeding can cause health problems because there is more chance of the organisms inheriting harmful genetic defects when the gene pool is limited.
-There can also be serious problems if a new disease appears because there is not much variation in the population.
-All the stock are closely related to each other, so if one of them is going to be killed by a disease, the others are also likerly to die from it.
Describe what is Meant by Genetic Engineering
Genetic engineering is when the genetic code of an organism is altered to acquire a desired trait.
Describe how the Gene Controls the Structure of the Protein
A gene encodes the order of amino acids in the specific protein encoded by that gene.
Describe how Genetic Engineering Works
-Genetic engineering involves isolating the desired gene from the original organism. To do this enzymes are used to cut the gene out of the genome.
-The desired gene is then transferred into a plasmid (in a bacterium). A virus could also be used.
-The plasmid or virus is used to transfer the desired gene into the target organism.
-It is essential that the gene is transferred at an early stage in an organism’s development. This is to ensure that the organism develops with the desired characteristics.
State Different Uses of Genetic Engineering
-Genes are introduced into crops for herbicide resistance so that the weeds will be killed but not the crop.
-Bacteria have been genetically modified to produce human insulin that can be used to treat diabetes. Bacterium are used as they reproduce rapidly.
-Scientists are researching genetic modification treatments for inherited diseases by faulty genes e.g. by inserting working genes into people with the disease. This is called gene therapy.
-Gene therapy could be used in humans to correct defective alleles and treat inherited disorders.
-Sheep have been genetically engineered to produce substances, like drugs, in their milk that can be used to treat human diseases.
Describe the Advantages of GM Crops
-GM crops generally produce a greater yield than normal crops or bigger or better fruit.
-GM crops can also be resistant to disease or insect attack.
-GM crops could be engineered to contain more nutrients.
Describe the Disadvantages of GM Crops
-Some say that growing GM crops will affect the number of wild flowers that live in and around the crops-reducing farmland biodiversity.
-Not everyone is convinced that GM crops are safe to eat and some people are concerned that we do not fully understand the effects of eating them on human health.
-Transplanted genes may also get out into the natural environment.
Describe Opposition to Gene Therapy
-We do not know the long term effects of gene therapy. For example, there is the possibility that if we change one gene, this might have an effect on other genes that we cannot predict.
-If we use gene therapy on an early stage embryo then every cell will contain the transferred gene.
-Once the human has grown into an adult, the transferred gene will also be in the gametes. This means that it could be transferred to their offspring and then on down to their offspring.
-Scientists cannot predict the long-term effects of the transferred gene. It is possible that many generations in
the future, the transferred gene will prove to be harmful.
Describe what is Meant by a Clone
A clone is a an organism that is genetically identical to another organism.
Describe the Advantage of Using Cloned Plants Rather than Plants Grown from Seeds
-Seeds are produced by plants which have undergone sexual reproduction.
-This means that the seeds contain a mixture of genetic information from two parents and we cannot accurately predict the features of the offspring plants.
-However, with cloned plants we can be absolutely certain of the features of the offspring as they are genetically identical to the parent.
Describe how Plants are Cloned Using Cuttings
-The plant with the required features is identified.
-A small part of the plant is removed.
-The stem is dipped into some rooting powder.
-The plant is then transferred to soil.
Explain why Taking Cuttings is Not Used for Large Scale Plant Production
-Large scale plant nurseries produce thousands of plants at a time.
-With cuttings, we take a section of the plant, for example a section of stem with several attached leaves.
-It would not be possible to take enough cuttings from one plant to satisfy the requirements of a plant nursery.
Describe how Plants are Cloned Using Tissue Culture
-The plant with the desired required features is identified.
-A tissue sample is scarped from the parent plant.
-The tissue samples are placed in Agar growth medium containing auxins and nutrients.
-The samples then develop into tiny plantlets and are placed into soil.
Explain why Plant Tissue Culture is Carried out Under Sterile Conditions
-In tissue culture, the tiny plantlets are grown on nutrient jelly.
-It is essential that this is kept sterile otherwise we would also grow microorganisms such as fungi and bacteria.
Explain why Plant Tissue Culture is Useful to Grow Plants on a Large Scale
-With tissue culture, we can produce thousands of identical plants quickly and cheaply.
-Because these are clones, we know exactly what characteristics the plants will have. This makes them ideal for plant nurseries.
