key area 1.7 - evolution

Question 1

evolution definition

Answer 1

• the process of gradual changes in organisms over generations due to genetic variations

Question 2

natural selection

Answer 2

• non random process that results in the increase in frequency of DNA sequences that increase survival and the non random reduction in frequency of deleterious sequences

Question 3

stabilising selection

Answer 3

• selection pressure against extreme variants of a phenotype
• leads to reduction in genetic diversity as mean value for trait stays the same

Question 4

directional selection

Answer 4

• selection favours a initially less common, extreme variant of a phenotype
• causes progressive shift in mean value for a trait
• common during period of environmental change

Question 5

disruptive selection

Answer 5

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

Question 6

vertical gene transfer

Answer 6

• genes are transferred from parent to offspring as a result of sexual or asexual reproduction
• sexual involves combination of genes and asexual clones show no variation

Question 7

horizontal gene transfer

Answer 7

• genes are transferred between individuals in the same generation
• this method of gene transfer is much quicker than vertical gene transfer
• this occurs in prokaryotes

Question 8

species

Answer 8

• a species is a group of organisms capable of interbreeding and producing fertile offspring

Question 9

natural selection process

Answer 9

• offspring 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)
• offspring which are better adapted to the environment will survive and reproduce passing favourable characteristics to the next generation
• less well adapted die
• this is repeated generation after generation so the organisms best suited to the environment are naturally selected which alters allele frequency

Question 10

speciation

Answer 10

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

Question 11

allopatric speciation

Answer 11

• largely interbreeding population
• population split into sub populations by a geographical barrier preventing gene flow
• different mutations occur in each population 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 12

sympatric speciation

Answer 12

• largely interbreeding population sharing same ecological niche
• an alternative ecological niche becomes available and some members of the population exploit that niche
• two populations 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