Chapter 18: Variation And Selection

Question 1

Describe variation

Answer 1

differences between individuals of the same species

Question 2

What is continuous variation

Answer 2

a range of phenotypes between two extremes; examples include body length and body mass

Question 3

What is discontinuous variation

Answer 3

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

Question 4

What is the cause of discontinuous and continuous variation

Answer 4

discontinuous variation is usually caused by genes only and continuous variation is caused by both genes and the environment

Question 5

Describe gene mutation

Answer 5

a random change in the base sequence of DNA

Question 6

What are the causes of genetic variation

Answer 6

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

Question 7

What increases the rate of mutation

Answer 7

ionising radiation and some chemicals increase the rate of mutation

Question 8

Describe an adaptive feature

Answer 8

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

Question 9

adaptive features of hydrophytes

Answer 9

-Stomata on top of leaf for gas exchange
-Have large air spaces in leaf for leaf to be buoyant (stay afloat)

Question 10

adaptive features of xerophytes

Answer 10

-Stomata in pits to reduce water loss
-Leaves rolled up or turn into thorns to reduce surface area for evaporation
-Thick waxy cuticle

Question 11

Natural selection

Answer 11

• variation within populations
• production of many offspring
• competition for resources
• struggle for survival
• reproduction by individuals that are better
  adapted to the environment than others
• passing on of their alleles to the next
  generation

Question 12

Describe adaptation

Answer 12

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

Question 13

Example of natural selection

Answer 13

development of strains of antibiotic resistant bacteria

Question 14

Selective breading

Answer 14

• selection by humans of individuals with
  desirable features
• crossing these individuals to produce the
  next generation
• selection of offspring showing the desirable features

Question 15

What is required for the success of selective breeding

Answer 15

selective breeding by artificial selection is carried out over many generations to improve crop plants and domesticated animals

Question 16

differences between natural and artificial selection

Answer 16

Cause of selection: artificial humans and natural environment
Speed of change: artificial fast and natural slow
Reason for selection: natural selective trait increase the organisms chance of survival and reproduction, artificial trait desirable to humans
Effect to fitness: natural improve fitness, artificial decreases fitness