18 Variation and selection

Question 1

variation

Answer 1

differences between individuals of the same species

Question 2

what does continuous variation result in

Answer 2

a range of phenotypes between two extremes

Question 3

example of continuous variation

Answer 3

body length and body mass

Question 4

what does discontinuous variation result in

Answer 4

a limited number of phenotypes with no intermediates

Question 5

examples of discontinuous variation

Answer 5

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

Question 6

what is discontinuous variation usually caused by

Answer 6

by genes only

Question 7

what is continuous variation caused by

Answer 7

genes and the environment

Question 8

mutation

Answer 8

genetic change

Question 9

how are new alleles formed

Answer 9

by mutations

Question 10

what increases the rate of mutation

Answer 10

ionising radiation and some chemicals increase the rate of mutation

Question 11

gene mutation is

Answer 11

a random change in the base sequence of DNA

Question 12

what are sources of genetic variation in populations

Answer 12

mutation, meiosis, random mating and random fertilisation

Question 13

adaptive feature

Answer 13

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

Question 14

explain the adaptive feaures of hydrophytes

Answer 14

Small roots - don’t need long, can absorb water/mineral ions from surrounding water, mainly used for anchorage.
Large air spaces in leaves - keep the leaf close to surface to float to absorb light for photo
stomata always open - no need to keep closed as constant supply of water
stomata found on upper epidermis - can exchange gas more easily with air
lack of waxy cuticle or very thick one - water loss isnt an issue OR waxy cuticle repels water to keep stomata clear
Lack of xylem - not as much need for water transport, water is absorbed through plant tissues
Floating seeds - for seed disperal away from parent so less competition

Question 15

explain the adaptive feaures of xerophytes

Answer 15

Rolled up leaves with stomata inside - prevents wind from blowing, traps layer of humid air and reduces water pot gradient
Thick waxy cuticle - reduces evaporation from the epidermis
hairs on underside - trap humid air next to stomata and reduces water pot gradient
needle leaves - reduce surface area
swollen stems - store more water
shallow roots - absorb water from lightest rainfall
deep roots - penetrate to very low water table

Question 16

describe natural selection

Answer 16

1. the individuals within a population show variation. THere is differences due to their genes
2. There is production of many offspring
3. there is competition for resources between individuals
4. There is struggle for survival ebtween individuals
5. Only the organisms that are better adapted to the environment will reproduce. ‘Survival of the fittest’.
6. The better adapted organism will pass on the more sucessful alleles to offspring of the next generation.

Question 17

describe selection breeding

Answer 17

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

Question 18

how long and why is selective breeding by artificial selection carried out

Answer 18

over many generations to improve crop plants and domesticated animals

Question 19

describe adaptation as a process

Answer 19

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

Question 20

example of natural selection

Answer 20

the development of strains of antibiotic resistant bacteria

Question 21

differences between natural and artificial selection

Answer 21

(about natural selection)
- features are adaptive for environment
- features are selected by environment
- there is compeition between individuals for resources
- prescence of predators, cold temps, food availabilty
- slower than artificial selection
- increases the ability to survive and reproduce
- maintains genetic variation/selective reduces genetic variation
- random mating (as opposed to planned mating)

Question 22

How do some bacteria become resistant to antibiotics

Answer 22

1. within a population of bacteria there is variation.
2. random mutations in genes can create new alleles that are resistant to certain antibiotics
3. the antibiotic acts as a selection pressure and kills the non resistant strains
4. there is less competition for resources
5. the surviving bacteria will be able to pass their resistant gene to their offspring when they reproduce
6. example of evolution by natural selection