what is variation and selection

Question 1

what is variation

Answer 1

differences between individuals of the same species

Question 2

how is phenotypic variation caused

Answer 2

Phenotypic variation is caused by both genetic and environmental factors

Question 3

what is continuous variation

Answer 3

Continuous variation is influenced by genes and environment, resulting in a range of phenotypes between two extremes, e.g. height in humans

Question 4

what is discontinuous variation

Answer 4

Discontinuous variation is caused by genes alone and results in a limited number of distinct phenotypes (e.g. you are either blood group O, A, B or AB, nothing else)

Question 5

what is a mutation

Answer 5

genetic change

Question 6

what is a gene mutation

Answer 6

a change in the base sequence of DNA

Question 7

how are new alleles formed

Answer 7

Mutation is the way in which new alleles are formed

Question 8

what affects the rate of mutation

Answer 8

Ionising radiation and some chemicals increase the rate of mutation

Question 9

what is down syndrome

Answer 9

Mutation is a source of variation e.g. in Down’s syndrome, where a parent’s chromosomes are unevenly distributed in meiosis. In fertilisation, a zygote with a number of chromosomes that is not 46 is created (e.g. 23 + 24). Characteristics: broad forehead, short neck, downward-sloping eyes, short nose and mental retardation.

Question 10

what is sickle cell anaemia

Answer 10

Disease in which the red blood cell has a sickle shape instead of a round biconcave shape, controlled by a recessive allele, which causes weakness, aching joints and poor circulation.

The fact that it is recessive means that a heterozygous person can be a carrier: they have the allele but it is not expressed.

Question 11

sickle cell anaemia and malaria relation

Answer 11

Being a carrier of sickle cell anaemia makes you resistant to malaria

In equatorial Africa, being sickle cell anaemic causes death, malaria causes death, but the carriers have immunity to malaria and have some symptoms of anaemia, in severe cases they are very weak.

Question 12

what are adaptive features

Answer 12

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

the inherited functional features of an organism that increase its fitness

Question 13

what is fitness

Answer 13

the probability of an organism surviving and reproducing in the environment in which it is found

Question 14

what are xerophytes

Answer 14

live in deserts where water is scarce and evaporation is rapid, or in windy habitats.

Question 15

features of xerophytes

Answer 15

Deep roots to reach water far underground

Leaves reduced spines with minimum surface area for transpiration

Shallow spreading roots to collect occasional rain

Rolled leaves, leaf hairs and stomata sunk in pits to trap moist air

Waxy leaf cuticle, impermeable water

Stomata opening at night and closed at midday when evaporation is highest

E.g. cactus and marram grass

Question 16

what are hydrophytes

Answer 16

live in wholly or partly submerged in water

Question 17

features of hydrophytes

Answer 17

Leaves are highly divided to create large surface area for absorption and photosynthesis

Very little cuticle formation

Lack of xylem tubes, no stomata underside of leaves

Stomata is in the upper surface, has a thick waxy layer to repel water and to keep the stomata open and clear

Roots are often reduced and root hairs are often absent

Question 18

what is natural selection

Answer 18

• The greater chance of passing on of genes by the best adapted organisms.
• The surviving organisms reproduce, since they don’t get eaten up, so variation has caused the species to evolve.
• Evolution is caused by natural selection which is caused by a change in the environment

Question 19

how does variation lead to natural selection

Answer 19

Variation is natural or random changes in all living organisms.

Variation leads to survival of the fittest since the variations in certain organisms allow that organism to have an advantage over the others in its species in that area

Question 20

what is artificial selection

Answer 20

Is breeding organisms with valued characteristics together in order to try to produce offspring which shares those useful characteristics (selective breeding).

Can be used to produce organisms which are more economically valued

Question 21

what is selective breeding

Answer 21

Selecting by humans of individuals with desirable features

Crossing three individuals to produce the next generation

Question 22

how are antibiotic resistant bacteria formed

Answer 22

Strains of antibiotic-resistant bacteria are developing as the use of antibiotics is increasing.

In a group of many bacteria, one might mutate to be resistant to the antibiotic, as a result it reproduces and the others die making a new strain of bacteria, which is resistant to antibiotics.

The susceptible (weak) bacteria are killed first

Only resistant (strong) bacteria are left