18. Variation and Selection

Question 1

What is 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

Question 3

What are 2 examples of continuous variation?

Answer 3

body length and body mass

Question 4

What is discontinuous variation?

Answer 4

a limited number of phenotypes with no
intermediates (a particular characteristic can be divided into distinct categories)

Question 5

What are 3 examples of discontinuous variation?

Answer 5

ABO blood groups, seed shape in peas and seed colour in peas

Question 6

What is discontinuous variation caused by?

Answer 6

usually ONLY genes

Question 7

What is continuous variation caused by?

Answer 7

both genes and environment

Question 8

Difference in what causes continuous and discontinuous variation

Answer 8

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

Question 9

Investigate discontinuous variation

Answer 9

1. give a control strip to each participant, have them write the number 1 on the strip in pencil
2. give the PTC test strips to each participant, have them write the number 2 on the PTC strip in pencil
3. each participant to place the control strip on their tongue, record its taste
4. each participant to place the PTC strip on their tongue and record its taste
5. record number of participants that could taste the PTC or not

Question 10

What is PTC and how could it be useful?

Answer 10

compound that either tastes very bitter or is virtually tasteless, depending on the genetic makeup of the taster
could be useful in testing discontinuous variation

Question 11

Investigate continuous variation

Answer 11

1. create a table to record the body lengths and arm spans of about 20 people
2. measure body lengths of all participants, record in your table.
3. measure the arm spans of the same people, record in your table

Question 12

What is a mutation?

Answer 12

genetic change

Question 13

What does mutation lead to?

Answer 13

mutation is the way in which new alleles are formed

Question 14

What are two factor that increase the rate of mutation?

Answer 14

ionising radiation (eg gamma rays, X-rays and high energy UV)
some chemicals

Question 15

What is gene mutation?

Answer 15

a random change in
the base sequence of DNA

Question 16

What are sources of genetic variation in populations?

Answer 16

mutation
meiosis
random mating
random fertilisation

Question 17

What is an adaptive feature?

Answer 17

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

Question 18

What are the adaptive features of hydrophytes?

Answer 18

large, thin leaves
most stomata on the upper surface rather than lower surface
little or no waxy cuticle on their leaves (water loss is not a problem)
long leaf stalks with large air spaces (helps them float)
reduced root system (do not need to be anchored in the ground)
aerial flowers to attract flying pollinators
poorly developed xylem tissue (allows transport of water but provides little support)

Question 19

What are the adaptive features of xerophytes to reduce water loss?

Answer 19

thick waxy cuticle covering the upper epidermis
few stomata/stomata that are sunken into pits surrounded by hair to reduce water loss by transpiration
curled/rolled/folded leaves, which reduce the SA for transpiration

Question 20

What are the adaptive features of xerophytes to store water?

Answer 20

thick succulent stem
widely spread roots, close to the surface (plant can absorb as much water as possible even when there is limited rainfall) OR very deep roots to reach underground water sources

Question 21

Explain the process of natural selection.

Answer 21

1. There is genetic variation in a population
2. Populations produce many offspring, more than can be supported in the habitat where they live
3. Competition between individuals for limited resources (eg food, mates or space)
4. Struggle for survival: some individuals are more likely to survive than others
5. Individuals better adapted to their environment are more likely to survive and reproduce, passing on their alleles to the next generation
6. Offspring of better adapted individuals are more likely to then be better adapted to the environment, survive and reproduce successfully than other individuals in the population

Question 22

Explain the process of selective breeding.

Answer 22

1. humans select individuals with
   desirable features
2. humans cross these individuals to produce the
   next generation
3. humans select the offspring showing the desirable features, only letting these reproduce as well

Question 23

When and why is selective breeding by artificial selection carried out?

Answer 23

carried out over many generations
to improve crop plants and domesticated animals

Question 24

What is the process of adaptation?

Answer 24

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

Question 25

Describe the development of strains of antibiotic resistant bacteria when treating with antibiotics.

Answer 25

1. During infection, bacteria reproduce quickly in body
2. As bacteria reproduce, mutations may occur that allow them to become antibiotic resistant
3. Resistant bacteria will have an advantage over the non-resistant bacteria, surviving the antibiotic treatment and reproducing, passing on the allele for antibiotic resistance to the next generation
4. Soon, the population will only contain bacteria that are antibiotic resistant

Question 26

Example of natural selection

Answer 26

development of strains of antibiotic resistant bacteria when using antibiotics

Question 27

Outline the differences between natural and
artificial selection.

Answer 27

Natural selection: reproductive success is driven by naturally occurring processes
Artificial selection: reproductive success depends on the choices of the breeder
Artificial selection reduces variation within a population
Artificial selection may cause negative effects due to inbreeding

Question 28

What is inbreeding and why may it be bad?

Answer 28

breeding closely related animals
this produces purebred offspring with particular traits
Risk that parents may carry recessive genes for undesirable traits, which may be passed on to their offspring