new information for a2 biology : adaptation and selection 2

Question 1

what is every organism subjected to?

Answer 1

every organism is subjected to a process of selection, based on its suitability for survival under the conditions that exist at the time

Question 2

• the environmental factors that limit the population of a species are called _________ _________
• these _________ _________ include _________, _______ and ___________
• these _________ _________ determine the _________ of all _______ ______ ___ ____ ____

Answer 2

• the environmental factors that limit the population of a species are called selection pressures
• these selection pressures include predation, disease and competition
• these selection pressures determine the frequency of all alleles within the gene pool

Question 3

what is a gene pool?

Answer 3

a gene pool is the total number of all alleles of all the genes of all the individuals within a particular population in a given time

Question 4

what did Darwin realise about all species? (read through)

Answer 4

Darwin appreciated that all species have the potential to increase their numbers exponentially

Darwin realised that, in nature, populations rarely, if ever, increased in size at such a rate. he rightly concluded that the death rate of even the most slow-breeding species must be extremely high. high reproductive rates have evolved in many species to ensure a sufficiently large population survives to breed and produce the next generation. this compensates for high death rates from predation, competition for food (including light in plants) and water, extremes of temperature, natural disasters such as earthquake, and fire, disease etc.

however, some species such as orcas and humans, have evolved lower reproductive rates along with a high degree of parental care. the lower death rates that result help to maintain their population size.

the link between over-production and natural selection lies in the fact that, where there are too many offspring for the available resources, there is competition amongst individuals (intraspecific competition) for the limited resources available. the greater the numbers, the greater this competition and the more individuals will die in the struggle to survive. these deaths, however, are not totally random. those individuals in a population best suited to prevailing conditions (e.g better able to hide from or escape predators, better able to obtain light or catch prey, better able to resist disease or find a mate) will be more likely to survive than those less well adapted. these individuals will be more likely to breed and so pass on their more favourable allele combinations to the next generation, which will therefore have a different allele frequency from the previous one. the population will have evolved a combination of alleles that is better adapted to the prevailing conditions. this selection process, however, depends on individuals of a population being genetically different from one another.

if an organism can survive in the conditions in which it lives, you may wonder why it doesn’t always produce offspring that are identical to itself. these will, after all, be equally likely to survive in these conditions, whereas variation may produce individuals that are less suited. however, conditions change over time and having a wide range of genetically different (and therefore phenotypes) in the population means that some will have the combination of genes needed to survive in almost any new set of circumstances. populations showing little individual genetic variation are often more vulnerable to new diseases and climate changes.

it is also important that a species is capable of adapting to changes resulting from the evolution of other species. the larger a population is, and the more genetically varied the individuals within it, the greater the chance that one or more individuals will have the combination of alleles that lead to a phenotype which is advantageous in the struggle for survival. these individuals will therefore be more likely to breed and pass their allele combinations on to future generations. variation therefore provides the potential for a population to evolve and adapt to new circumstances.

Question 5

what is the process for answering questions on natural selection?

Answer 5

variation exists due to mutation

changing environment – look at question stem

allele = selective advantage

individuals survive and reproduce

pass on alleles (name of)

allele frequency in gene pool increases