DNA and the Genome - Evolution

Question 1

directional

selection

Answer 1

• selection favours one extreme of the phenotype
• results in a progressive shift in a population’s mean value for a trait

Question 2

disruptive

selection

Answer 2

• selection favours extreme versions of a phenotype
• results in a population being split into two distinct groups, each with its own mean value for a trait

Question 3

evolution

Answer 3

the process of gradual changes in the inherited characteristics of organisms over generations as a result of genomic variations

Question 3

horizontal inheritance

Answer 3

• transfer of genetic material ‘sideways’ between members of the same generation in a population
• provides potential for much faster evolutionary change than vertical inheritance

occurs in prokaryotes

Question 4

natural selection

definition

Answer 4

a non-random process that results in the increase in frequency of the DNA sequences that confer a selective advantage and the reduction in frequency of deleterious sequences

deleterious sequences provide a selective disadvantage

Question 5

natural selection

process

Answer 5

• organisms produce more offspring than the environment can support
• members of a species show variation
• struggle for existence occurs due to selection pressures (disease, competition, predation)
• those better adapted survive and reproduce passing on adaptations to their offspring
• this process is repeated generation after generation and organisms best adapted to the environment are naturally selected for, predominating the population, thus allele frequency is altered

Question 6

stabilising

selection

Answer 6

• selection against the extreme varients of a phenotype
• leads to a reduction in genetic diversity (the mean value for a trait stays the same)

Question 7

vertical inheritance

Answer 7

transfer of genetic information ‘down’ to the next generation by sexual or asexual reproduction

sexual = combinations of genes
asexual = clones show no variation

Question 8

speciation

definition

Answer 8

speciation is the generation of the new biological species by evolution as a result of isolation, mutation, and selection

allopatric and sympatric

Question 9

allopatric speciation

process

Answer 9

• largely interbreeding population
• population split into subpopulations by a geographical barrier preventing gene exchange
• different mutations occur in each subpopulation resulting in variation within each group
• natural selection affects each group differently
• over a long period of time natural selection increases the frequency of new alleles causing gene pools to be altered making the groups genetically distinct and unable to interbreed to produce fertile offspring

Question 10

sympatric speciation

process

Answer 10

• largely interbreeding population sharing same ecological niche
• an alternative ecological niche becomes available and some members of the population exploit that niche
• two poopulations exploit different resources and no longer interbreed
• mutations produce new variation in each group but they are not shared; mutants are better adapted to exploit their niche
• genetic sequences for adaptations in each niche are favoured by natural selection causing gene pools to be altered making the groups genetically distinct and unable to interbreed to produce fertile offspring

Question 11

species

Answer 11

a species is a group of organisms which can interbreed to produce fertile offspring and which does not normally breed with other groups