4.2 How do organisms become so well adapted? Flashcards
What is evolution?
A change in allele frequency in a population over time.
How does evolution occur by natural selection?
1) A population has some naturally occurring genetic variation with new alleles created through mutations.
2) A change in the environment causes a change in the selection pressures acting on the population
3) An allele that was previously of no particular advantage now becomes favourable
4) Organisms with the allele are more likely to survive, reproduce, and so produce offspring
5) Their offspring are more likely to have the allele, so it becomes more common in the population.
How are headlice becoming resistant to headlice shampoos?
Over the centuries many different mutations have produced different alleles. There is a lot of genetic variation in the head louse population due to the large number of different alleles.
Drug companies develop shampoos with chemicals to kill the lice and for a while, most are killed. A few remaining head lice survive because they happen to have alleles that make them resistant to the chemicals. The survivors breed, producing offspring that inherit the resistant alleles. These alleles for resistance to the chemical become more common. Soon, almost all head lice are resistant.
What are the agents of selection in natural selection?
The biotic and abiotic factors of the environment.
What is the gene pool?
Consists of all the alleles of all the genes present in a population.
What can the Hardy-Weinberg equation be used to calculate?
The frequencies of alleles and genotypes in a population
What are the conditions in which the Hardy-Weinberg equations apply?
1) No selection is taking place
2) No mutations are occurring
3) mating is random
4) no migration is taking place
5) The population is large
What is the Hardy-Weinberg equation?
p² + 2pq + q² = 1
Where p² is the frequency of homozygous dominant individuals
2pq is the frequency of heterozygous individuals
q² is the frequency of homozygous recessive individuals
What will the ability of a population to adapt to new conditions depend on?
1) Strength of selection pressure
2) Size of gene pool
3) Reproduction rate of the organism
Can populations ever become perfectly adapted to their environment? Why?
No because when the environment changes, there is a time lag before a population can adapt by natural selection, so organisms are always trying to catch up.
Even in a stable environment, mutations are occurring, many of which are harmful to the organism, making a population less well adapted to its surroundings.
What is reproductive isolation?
Two populations are described as being reproductively isolated when they are unable to breed with each other, or they produce offspring which fail to survive.
What is speciation?
Formation of a new species
