Evolution

Question 1

Name the type of isolating mechanism that prevents interbreeding between these three snail populations.

Answer 1

geographical

Question 2

State the term used to describe the random changes in allele frequency in a small population.

Answer 2

genetic drift

Question 3

suggest how an ancestral species might have evolved into the two species, B. pratorum and B. terrestris.

Answer 3

1 idea of isolation / isolating mechanism / barrier ;
2 seasonal (difference) / temporal (difference) /
males and queens (in different populations) produced
in different months /
breeding (in different populations) in different months ;
3 behavioural (difference) / visit different (types of) flowers /
feed at different times / feed on different food types ;
4 different flower locations / different (micro)habitats ;
5 idea that gene flow restricted /
no gene flow (between populations) ;
6 different adaptations / specialisation / niche partitioning ;
3

Question 4

Explain, using scientific terms, why a collection of small islands remote from the mainland provides optimal conditions for speciation.

Answer 4

1 geographical, isolation / separation / barrier ;
2 idea of reproductive isolation ;
3 different , selection pressures / adaptations
(on different islands) ;
4 small , populations / gene pools ;
5 idea of mp 4 resulting in founder effect ;
6 idea of mp 4 resulting in greater genetic drift ;

Question 5

Suggest how different types of isolating mechanism allowed dogs to evolve separately to wolves.

Answer 5

1 geographic ;
2 wolves avoid human settlements / dogs confined by humans ;
3 behavioural ;
4 detail / description ;
5 mechanical ;
6 idea of different size of wolves and some small dogs ;
7 gamete incompatibility ;
8 possibility of different chromosome numbers ;
9 seasonal / temporal ;
10 different breeding, seasons / times ;

Question 6

explain the problems of classifying wolves and different dog breeds according to:
• the biological species conceptand
• the phylogenetic species concept.

Answer 6

biological species concept
1 (members of same species) need can interbreed to produce
fertile offspring ;
2 not all dog breeds can do this therefore not same species ;
3 dog and wolf can so they should be same species ;
phylogenetic species concept
4 idea that dogs and wolves monophyletic group / tip of
phylogeny ;
5 genetic differences, between dogs and wolves small ;
6 gene flow between wolves  big dogs  little dogs
/ analagous to ring species ;
7 (PSC) one species (with a lot of phenotypic variation) ;

Question 7

State the two essential steps that must have occurred for a breed to develop a distinctive metabolism, such as the ability to eat mainly seaweed.

Answer 7

mutation / described ;

selection / selection pressure / selective advantage ;

Question 8

Suggest what particular problems make the North Ronaldsay breed one of the most endangered sheep breeds in the United Kingdom.

Answer 8

1 small , population / gene pool ;
2 ref. inbreeding / genetic drift ;
3 unusual diet / cannot eat grass / poisoned by grass /
must eat seaweed ;
4 may not be commercially viable / expensive to keep ;

Question 9

State why the English Elm clone is genetically isolated from other varieties of elm.

Answer 9

rarely / do not , produce seed / cross-pollinate / interbreed ;
only reproduce asexually ;

Question 10

Over time, the frequency of this new allele increased in the gene pool of the human populations whose diet included milk.Name the process by which this increase occurred.

Answer 10

natural / directional , selection

Question 11

Suggest why information gained from studying such model organisms can be applied to humans.

Answer 11

similar / same, cells / metabolism ;
similar / same / share, genes 
or have genes in common ; 
similar / same, (embryonic) development ; 
shared, ancestry / ancestor 
or all related by evolution ;

Question 12

One allele of DRD4 has been found more frequently amongst individuals whose personality is described as ‘novelty-seeking’ and whose behaviour tends to be exploratory and impulsive.
Suggest how this particular allele of the DRD4 receptor could have become common in the human population.

Answer 12

natural selection ;
selective advantage ;
(allele / behaviour) increases, survival / breeding / AW ;
(because) helped, find food / find new resources /
make new tools / get mates ;
allele passed on (to next generation) ;
(allele / behaviour) increased in frequency over,
generations / time ;