Variation and Selection Flashcards
Variation
differences between individuals of the same species
Continuous variation
results in a range of phenotypes between two extremes; examples include body length and body mass.
Discontinuous variation
results in a limited number of phenotypes with no
intermediates; examples include ABO blood groups, seed shape in peas and seed
colour in peas
Discontinuous variation is usually caused by
genes only and continuous variation is
caused by both genes and the environment.
Mutation
genetic change
The mutation is the way in
which new alleles are formed?
Ionising radiation and some chemicals increase the
rate of mutation.
Gene mutation
random change in the base sequence of DNA.
sources of genetic
variation in populations
Mutation, meiosis, random mating and random fertilisation
An adaptive feature
the inherited feature that helps an organism to survive and
reproduce in its environment, i.e. increase fitness.
Adaptive features of hydrophytes:
1 submerged leaves are divided ;
2 providing large area for, photosynthesis
/ absorption ;
3 leaves have large surface area ;
4 to float ;
5 (floating leaves so) little xylem/ little
lignin ;
6 water provides support ;
7 little/ no roots /root hairs ;
8 roots for anchorage only / no need for
roots to absorb water or mineral ions ;
9 little/ no, cuticle ;
10 no need to conserve water ;
11 stomata only on upper surface ;
12 only upper surface exposed to air/ to
allow diffusion of gases ;
13 lots of air spaces (between cells) ;
14 for flotation/ buoyancy ;
15 floating leaves ;
16 to allow, diffusion/AW of (named)
gas(es) ;
17 aerial roots ;
18 to allow roots to receive oxygen ;
Adaptive features of xerophytes:
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 ;
deep roots / AW ;
to absorb water from the water table /
AW
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 / AW ;
roots branch many times ;
have many roots hairs ;
to give a large surface area (for
absorption of water) ;
Natural selection:
genetic variation within populations
production of many offspring
struggle for survival, there is competition for resources
a greater chance of reproduction by individuals that are better adapted to the
environment than others
these individuals pass on their alleles to the next generation
Selective breeding:
selection by humans of individuals with desirable features
crossing these individuals to produce the next generation
selection of offspring showing the desirable features.
Selective breeding by artificial selection is carried out over
many generations to
improve crop plants and domesticated animals