pack 20 natural selection

Question 1

what does natural selection cause

Answer 1

natural selection is the process that leads to evolution

Question 2

what does evolution mean

Answer 2

evolution is the change in the frequency of alleles within a population over many generations

Question 3

name the 3 cause of genetic variation

Answer 3

-mutations
- meiosis
- random fussion of gametes

Question 4

what causes selection pressures and how

Answer 4

predation, disease, competition and changes in the environment result in selection pressures giving some phenotypes a selective advantage acting as a trigger for natural selection to occur.

Question 5

describe the process of natural selection

Answer 5

• there is a variation in a population
• this is due to a mutation, giving rise to new alleles of a gene
• organisms with the advantageous allele, will have a phenotype that gives them a selective advantage in their environment
• organisms with the advantageous alleles are more likely to survive to reproduce or at least have more offspring than others
• these organisms are therefore more likely to pass on their advantageous alleles to the next generation than the others
• this causes an increase in the frequency of the advantageous allele in the population over many generations

Question 6

name the 3 different adaptations and description

Answer 6

-anatomical- changes to the organisms body
- physiological- haemoglobin with different oxygen affinity
- behavioural - better food search strategies

Question 7

name the 3 types of natural selections

Answer 7

• directional
• stabilising
• disruptive

Question 8

what is directional selection

Answer 8

• directional selection acts against one of the extreme phenotypes and selects the other
  -results in an increase in the frequency of alleles

Question 9

what is stabilising selection

Answer 9

• acts against both the extremes in a range of phenotypes i.e favours the middle phenotypes and so acts to prevent change

Question 10

what is disruptive selection

Answer 10

• individuals with both extremes of a phenotype have a selective advantage over those in the middle so both are selected

Question 11

what does species mean

Answer 11

a group of organisms with similar characteristics that can interbreed to produce fertile offspring

Question 12

what does speciation mean

Answer 12

speciation is a process whereby one gene pool gives rise to more than one gene pool.

Question 13

what are the two types of speciation

Answer 13

• allopatric
• sympatric

Question 14

where does this occur - allopatric

Answer 14

when two populations of the same species becomes geographically separated by a physical barrier

Question 15

what is allopatric speciation

Answer 15

• parts of population becomes geographically isolated
• no interbreeding occurs between the populations
• different environments lead to different selection pressures
• different beneficial mutations may occur leading to formation of different advantageous alleles
• in each population organisms with the advantageous phenotype will be more likely to survive an reproduce than those without, and so the allele frequencies in each population will cahnge over many generations
  eventually the genotype of the two populations may become so different that, even if members of each grop were reunited, they would no longer successfully interbreed to produce fertile offsprings
• the two populations are now classified as different species

Question 16

what is reproductive isolation

Answer 16

a set of barriers that exist between different species that make them unable to breed and produce healthy offspring - in sympatric speciation it is the presence of a random mutation

Question 17

what are the causes of sympatric speciation

Answer 17

seasonal temporal
mechanical
behavioural

Question 18

what is seasonal temporal isolation

Answer 18

members of the two populations reproduce at different times of the year (example flowers)

Question 19

what is mechanical isolation

Answer 19

anatomical differences may prevent mating occurring, for example, it may be physically impossible for the penis to enter the vagina in mammals

Question 20

what is behavioural isolation

Answer 20

members of two populations have different courtship patterns

Question 21

what is sympatric speciation

Answer 21

• occurs in the same habitat / environment / population
• mutations causes different advantage
• this leads to reproductive isolation
• different alleles are passed on
• this causes a change in frequency of alleles
• eventually different species cannot interbreed to produce fertile offspring.