B14 Flashcards
Variation and evolution
How does variation come about ?
- nature
[] genetic inheritance of variation - nurture
[] variation due to an individual’s environment - sometimes, variants between individuals may be due to a combination of both genetics and environment, for example weight and skin colour
How is (genetic) variation in a species caused, and what is its effect on the population (especially if the environment changes) ?
- through genetic mutations during cell division
[] most mutations have no effect on the phenotype of an organism
[] some mutations influence the phenotype of an organism - for example, alleles that MAY lead to tallness if the individual is in the right environmental conditions
[] some mutations determine the phenotype, like for eye and natural hair colour - sometimes genetic mutations can lead to a NEW phenotype and thus introduce new variants into populations
[] if the new phenotype is useful to survival, it spreads across the population as it gives the individuals who have it more chances to survive and reproduce, passing along the useful new allele
[] if the environment changes and the new phenotype is useful in this new environment also, the process of inheritance of the new allele is sped up due to the increased rate of deaths/non-success to breed for other members of the population that do not have the allele
What is selective breeding ?
A process where humans artificially breed organisms to inherit and enhance desired characteristics
[] faster than evolution by natural selection
What is a phenotype ?
The observable physical characteristics of an organism
What is a genotype ?
The combination of alleles that an organism possesses for a certain gene
[] these determine or influence the phenotype
Why is selective breeding useful for humans ?
- can help to increase food security worldwide or make certain products for sale
[] breeding crops that produce bigger or more grains, fruit or biomass
[] breeding animals that produce more meat, milk, eggs etc.
[] breeding animals that produce higher qualities of meat, milk, eggs etc.
[] animals that produce larger quantities of wool and higher qualities of wool - can be used to select certain aesthetic features
[] brighter, bigger, more rarely-coloured flowers in horticulture
[] domestic animals with certain colouration and features (eg. floppy ears, short fur, sloped backs, size) - can be used to breed animals with a certain temperament
[] useful for breeding working animals, domestic animals etc.
Describe how people selectively breed organisms
- variation exists within organism population
- organisms with the desired traits are selected and bred
- offspring are observed as they mature/grow
- offspring with the most desired traits are again selected and bred
- this is repeated over many generations until all of the offspring display the desired characteristics
Describe some problems/limitations of selective breeding
- limits gene pool more than natural selection
[] very harmful to a population if a change in the environment occurs, as very few will have different phenotypes than the rest of the population and thus one very few will survive that change
[] also leads to increased inheritance of genetic disease/defects or genetic susceptibilities to certain diseases (inbreeding)
What is genetic engineering ?
When genes are artificially transferred to the cells of other organisms at early stages of their development so that they mature with the desired trait
How is genetic engineering done (in general) ?
- done in early stages of development for animals (embryonic stage) and for plants can be done in the meristem
- enzymes used to “cut out” the required gene from an organism
- gene inserted into a vector like a bacteria or virus using more enzymes
- the vector is used to insert the genes into the required organism’s cells
Describe how bacteria are genetically engineered to produce insulin for medical use
- enzyme “cuts out” insulin producing gene in a human (pancreatic) cell
- plasmid from bacterium is removed and split open by another enzyme
- insulin gene is inserted into plasmid by another gene
- plasmid is taken up by a bacterium
- this bacterium multiplies via binary fission
[] since all offspring are genetically identical, the new bacterial colony now all have the modified insulin-containing plasmids - insulin gene is switched on, and the bacteria secrete insulin which is then harvested and processed so that it is ready for medical use
Why is genetic engineering useful to humans ?
- can make other organisms produce complex human hormones, like insulin, for medical use
[] animals can even be made to produce these in their milks, like human growth hormone (HGH); used to make baby formula for new-borns whose mothers cannot lactate enough or whose breast-milks contain less HGH and nutrients than needed for proper growth - increasing food security by making plants and animals with bigger yields of food, or with disease/flood/heat/drought resistance
- genetically engineering lab animals like mice to replicate human diseases can help scientists to study these diseases and test cures/treatments
Describe some GM crops’ engineered features
- potatoes with more starch and pest/disease resistance
- plants that glow in the dark when needing water
[] bioluminescent jellyfish gene used - rice crops able to survive in more waterlogged soil conditions whilst giving a bigger yield of grain
- GM grasses that can break down explosive residues in soil from wartime
What is a clone ?
Genetically identical offspring to the parent that have been produced asexually
Describe the older, simpler method of cloning plants
- taking cuttings of leaves, stems etc. from the parent plant
- planting these cuttings to produce a new, genetically identical plant
- used widely by gardeners etc., not much in industry due to the use of larger parts of the parent plant meaning that less clones per parent plant can be made
Describe how tissue culturing is used to produce many plant clones
- tiny tissue sample taken from parent plant
[] placed in agar gel in a petri dish with a combination of different nutrients and plant hormones essential to growth (like gibberellins, auxins etc.) - nutrients + hormones in the agar gel allow the tiny tissue samples to grow into bigger masses of tissue called calluses
- these calluses are then moved to a new petri dish with agar with a different combination of hormones and nutrients to stimulate their growth into many, tiny, identical plantlets
- these plantlets can then be grown in soil in the normal way
Why is tissue culture more useful than taking cuttings for cloning plants ?
Can make many more clones per parent plant, so is more efficient in industry
- is also CRUCIAL in the preservation of rare plant species, as many clones can be made from a limited amount of parent plants
- HOWEVER, due to the increased equipment needed it is more expensive
How is embryo cloning used in (farm or domesticated) animals to increase the quality of offspring produced ?
- maternal and paternal animal parents with highest quality of certain traits are selected for breeding
- mother is given fertility hormones to stimulate maturation and ovulation of eggs
- eggs can be harvested at the point just before ovulation, or left in the mother animal
- the eggs are fertilised with the father’s sperm either in a lab or in the mother
[] if fertilised via natural insemination, the embryos are harvested from the mother after fertilisation - the embryos are split to harvest their undifferentiated cells, and each is allowed to grow into its own embryo
- these top-quality embryos are then implanted back into the original mother as well as many other mothers of the species so that as many top-quality cloned offspring as possible can be produced within a generation
Why is cloning animals useful to humans ?
- many animals may only be able to produce small amounts of offspring within their working lives, so maximising the quality of these offspring means that artificial selection of certain desired traits is much quicker
- top-quality embryos can be transported to areas where there is poor local stock, and once implanted, birthed and matured, the quality cloned offspring can mate with the poor local stock to produce a population of animals that have better traits in terms of food or material production, increasing food and economic security
Describe the process of adult cell cloning to “truly” clone animals
- adult body cell from animal A is retrieved
- mature egg cell from animal B is retrieved
- animal B’s egg cell has its nucleus removed (enucleation)
- animal A’s body cell has its nucleus removed and is inserted into the empty egg cell of animal B
[] the egg cell now acts as if it is fertilised due to having the full number of chromosomes from animal A instead of the usual number in gametes (half of the number of total chromosomes) - the egg cell with animal A’s nucleus is stimulated to divide mitotically to form an embryo with a small electric shock
- the embryo is inserted into a female animal to continue development and be born
- the final offspring is a genetic clone of animal A
Describe the benefits and risks of adult cell cloning in animals
benefits
- could be used to save animals from extinction or even bring animals (partially) back from extinction using DNA found in fossilised remains
- could be used to clone medically useful animals
[] like those genetically engineered to produce human hormones/proteins in milks etc.
- could be used to help infertile couples
risks
- genetic cloning of humans could be abused by some people
[] could lead to things like eugenics
- cloning reduces variety in a population, meaning that a population is more susceptible to extinction if conditions change
- personal objections from religious people about interference with natural reproduction
- ethical concerns about abuse of cloning
Describe the (potential) benefits and disadvantages of genetic engineering techniques
benefits
- genetic engineering can be used to cure inherited human disorders like diabetes, cystic fibrosis etc
- can be used to cure human disorders developed later in life like macular degeneration
- can be used for medicinal purposes such as producing crops with higher levels of vitamins that humans often have deficiencies of, insulin hormones for injection, or baby formulas for infants who are not able to derive the needed nutrients and HGH from their mother’s milk
- can be used to increase food security when used for farm animals and crops
- can be used to model human diseases in lab animals to enable scientists to better study and develop treatments against them
disadvantages
- some people have ethical objections to the ways in which trials of GM crops are run
- concerns about growing pesticide-resistance in insects that eat GM crops which produce their own pesticides
- some people have concerns about adverse health effects of eating GM crops and animals
- some have concerns as to GM crops’ genes spreading into natural, wild populations and affecting them negatively
- ethical concerns about use in eugenics or “designer” babies
