17. Variation and selection

Question 1

Describe variation, continuous variation, discontinuous variation

Answer 1

differences between individuals of the same species.

continuous variation is caused by both genes and the environment & results in a range of phenotypes between two extremes; examples include body length and body mass.

discontinuous variation is caused by genes only & results in a limited number of phenotypes with no intermediates; distinct categories, examples include ABO blood groups, seed shape in peas and seed colour in peas.

Question 2

Describe mutation

Answer 2

gene mutation as a random change in the base sequence of DNA- genetic change

mutation is the way in which new alleles are formed

ionising radiation and some chemicals increase the rate of mutation

Question 3

sources of genetic variation in populations

Answer 3

mutation, meiosis, random mating and random fertilisation are sources of genetic variation in populations

mutation- change in the gene

meiosis- gametes contain dif combo of alleles

random mating and random fertilisation- gametes

Question 4

Describe an adaptive feature

Answer 4

an inherited feature that helps an organism to survive and reproduce in its environment

Question 5

Explain the adaptive features of xerophytes

Answer 5

ABSORB WATER- deep roots to absorb water from the water table ;

long and spread out below the surface ;
to absorb water when it rains ;

root cells have low water potential ;
to absorb water by osmosis ;
from (very) salty soils ;

roots branch many times ;
have many roots hairs ;
to give a large surface area (for absorption of water) ;

REDUCE WATER LOSS- few stomata / low stomatal density ;
sunken stomata ;
stomata close during the day and open at night ;
rolled leaves ;
thick epidermis / thick cuticle ;
few / no / small, leaves ;
hairs on leaves ;
low rates of transpiration

Question 6

Explain the adaptive features of hydrophytes

Question 7

Describe natural selection

Answer 7

(a) genetic variation within populations

(b) production of many offspring

(c) struggle for survival, including competition for resources

(d) a greater chance of reproduction by individuals that are better adapted to the environment than others

(e) these individuals pass on their alleles to the next generation

Question 8

Describe adaptation

Answer 8

the process, resulting from natural selection, by which populations become more suited to their environment over many generations

Question 9

development of strains of antibiotic resistant bacteria is an example of natural selection

Answer 9

resistance arises by mutation ;
in small number of bacteria ;
ref. to a random event (not related to presence of antibiotic);
antibiotic kills bacteria that do not have the mutation / AW ;
resistant bacteria have no competition ;
resistant bacteria reproduce ;
pass on, gene / allele, for resistance ;
natural selection ;
method of transmission from one person to another described ;
gene transferred to other bacteria (of different type) in a plasmid ;

Question 10

Describe selective breeding

Answer 10

(a) selection by humans of individuals with desirable features

(b) crossing these individuals to produce the next generation

(c) selection of offspring showing the desirable features

Question 11

how selective breeding by artificial selection is carried out over many generation

Answer 11

to improve crop plants and domesticated animals

select, parent(s) / sheep / AW, with, fine / thin, hairs (in wool)
cross them together / use artificial insemination / IVF / AW ;

measure / AW, the hairs in the wool of all the offspring ;
select offspring with, fine / thin, hairs (in wool) ;
cross / AW, offspring together ;

continue / repeat, selection and/or breeding ;
over many generations ;

Question 12

differences between natural and artificial selection

Answer 12

features are, adaptive caused by environment ;
competition between individuals for (named) resource(s) ;
slow(er) ;
maintains (genetic) variation / less (genetic) variation in random mating ;
increase in fitness ;
explained: ability to survive AND reproduce (in natural environment) ;
selective breeding ;

humans choose, specific features / desired features ;
humans choose, individuals / offspring, to reproduce ;
selection not influenced by environment / humans manipulate environment ;
decreases (genetic) variation / decreases size of gene pool ;
faster / shorter ;
for economic / aesthetic, reasons ;
no / less, evolution ;
decrease in fitness ;