18.3 Natural selection

Question 1

What are the environmental factors that limit the population of a species called

Give 5 examples

Answer 1

Selection pressures

eg predation, disease, competition, natural disasters, fire

Selection pressures vary from time to time and place to place

Question 1

What do selection pressures determine

Answer 1

The variation of alleles in a gene pool

Question 2

What is a gene pool

Answer 2

The total number of alleles of all the genes, of all the individuals in a particular population at one time

Question 3

What factors must there be for natural selection to occur

Answer 3

. Organisms produce more offspring than can be supported by the availability of food, sunlight, space

. There is genetic variety within the populations of all species

. There must be a variety of phenotypes that are selected against, and some that are selected for

Question 4

Charles Darwin said that all species have the ability to increase exponentially. However, this never really occurs in populations, why

Answer 4

The death rate in species must be extremely high

And high reproductive rates have evolved in many species to compensate for the high death rate, so there can still be a large population to reproduce.

Either high reproductive rates can occur, or some species may chose to have few offspring but look after them more and ensure to provide the right conditions

There is a high death rate due to disease, competition, predators

Question 5

What is intraspecific variation

Answer 5

Where there are too many offspring within the same population for the available resources, so there is competition for the resources amongst individuals

The greater the numbers, the greater the competition for the resources so more individuals will die

Question 6

Describe the process of natural selection

Answer 6

The individuals in the population who have the phenotype best suited to the environment, eg if they can camouflage more to hide from predators, or have thicker fur for cold climates..

will survive more than others so are more likely to breed and pass down these favourable allele combinations to the next generation.

So the next generation will have a different allele frequency to the previous one, so the population will have better adapted characteristics

Question 7

Can variation produce individuals that are less suited to the environment?

Why can this be good

Answer 7

. Sometimes, individuals will have mutations that will produce offspring that are less adapted to the environment than the original parent

. It can be good because conditions can change over time, so having a wide range of phenotypes in the population means that some will have the right genes to survive in adverse conditions so the population can continue to grow and survive

Question 8

Why is having a big population size good

Answer 8

The larger a population is, the more genetically varied the individuals in it are, so the greater chance that one or more will have the combination of alleles that lead to a phenotype which is advantageous in the struggle for survival

So these individuals will be more likely to breed and pass down the allele combinations down to the future generations

So variation therefore provides the potential for a population to evolve and adapt to new circumstances