Variation

Question 1

Define discontinuous variation

Answer 1

Qualitative differences falling into discrete categories. No intermediate categories. Usually affected by one or two genes.

Question 2

Give an example of discontinuous variation

Answer 2

E.g blood type

Question 3

Define continuous variation

Answer 3

Quantitative differences between phenotypes. Wide range of variation in the population. Usually affected by both genetics and environment.

Question 4

Give an example for continuous variation

Answer 4

e.g. height

Question 5

What is a cause of discontinuous variation

Answer 5

Usually different alleles at a single gene locus have a large effect on the phenotype

The environment has a limited effect on the phenotype

Question 6

What is a cause of continuous variation

Answer 6

Many different alleles at a single gene locus having small effects

Different gene loci have the same, often additive effect on the phenotype

A large number of different gene loci (polygenese) may have a combined effect on the trait

The environment has a large effect on the phenotypic trait

Question 7

Define gene pool

Answer 7

The sum total of all the different alleles in a population

Question 8

Define allele frequency

Answer 8

How often an allele occurs in a population and is expressed as a decimal. The frequency can change over time due to evolution.

Question 9

What is the hardy weinburg principle

Answer 9

A method to predict the frequency of alleles in a population wont change from one generation to the next

Question 10

What are the hardy weinburg principle assumptions

Answer 10

The population is large
Mating is random
No selective advantage to any particular phenotype
No mutations, migrations or genetic drift

Question 11

What is the Hard weinburg calculation

Answer 11

P= frequency of dominant allele A
Q= Frequency of recessive allele a

Frequency of homozygous dominants: P^2
Frequency of homozygous recessive: Q^2
Frequency of heterzygous: 2PQ

Allele frequencies: P+Q =1
Genotype frequencies: P^2 + 2PQ + Q^2 =1

Question 12

Describe genetic drift

Answer 12

Due to chance. There will be variation in the population but by chance one particular allele may be passed on rather than another. If this process is repeated over many generations then the allele frequency will decrease.

Question 13

Describe a genetic bottleneck

Answer 13

When an extreme event occurs causing a big reduction in the size of a population. This means that genetic drift has a greater effect.

Question 14

What is natural selection

Answer 14

Genetic variation means that some organisms will have a better chance of survival than others. These organisms are better adapted, more likely to survive, breed and pass on their alleles to the next generation. This increases the chance of the advantageous alleles being passed on to the next generation and the allele frequency increasing.

Question 15

Define selection pressure

Answer 15

Environmental factor that confers greater chances of surviving and reproducing on some members of the population than others.

Question 16

What is the biological species concept

Answer 16

A group of similar organisms capable of interbreeding, producing fertile offspring and that are reproductively isolated from other such groups.

Question 17

What is the phylogenetic species concept

Answer 17

A group of organisms that show a close similarity in morphological, physiological, embryonic, ecological and behavioural characteristics forming the basis of classification showing an evolutionary lineage.

Question 18

Define clade

Answer 18

Group consisting of a single common ancestor and all the descendants of the ancestor and from a monophyletic group

Question 19

Define speciation

Answer 19

A large population of organisms may be split into sub groups by various isolating mechanisms the sub group then evolves through natural selection and are unable to interbreed to produce fertile offspring.

Question 20

How does geographical isolation occur

Answer 20

Organisms are separated by a physical barrier such as a river or mountain. The sub group becomes genetically isolated and experiences different selection pressures, different alleles may become favourable and the population will evolve through natural selection.

Question 21

What does geographical isolation lead to

Answer 21

Allopatric speciation

Question 22

What does reproductive isolation lead to

Answer 22

Sympatric speciation

Question 23

How does reproductive isolation occur

Answer 23

Differences in courtship, mechanical problems, gamete incompatibility, hybrid sterility. The sub group becomes genetically isolated and experiences different selection pressures, different alleles may become favourable and the population will evolve through natural selection.

Question 24

What are ecological barriers

Answer 24

When two species live in the same area at the same time but rarely meet so do not interbreed.

Question 25

What are temporal barriers

Answer 25

When two species live in the same place but do not interbreed because they are not active ta the same time of the day or do not reproduce at the same time of the year

Question 26

What is selective breeding

Answer 26

Breeder chooses an individual with desirable phenotypes for breeding and prevents those with undesirable features from breeding. The process is repeated over many generations this then increases the allele frequency for the desirable trait in the population.

Question 27

Describe the selective breeding process in cows

Answer 27

Performance testing: Each cows milk yield is measured and recorded.
Progeny testing: The offspring of bulls are tested to find which have produced daughters with high milk yield, aiding in determing the genotype of the bull.
A few good bulls are required to provide semen to artificially inseminate many cows
Cows with high milk production are given hormones to super ovulate and the eggs are flushed out

Question 28

Give a disadvantage of using artificial selection in dairy cows

Answer 28

Udders can become inflamed leading to mastitis

Diary cows can have strain on their legs due to increase size of their udders.

Question 29

Describe artificial selection using bread wheat

Answer 29

Has lead to increase yield, higher protein content, shorter stalks to prevent bending in the rain and wind. Disease resistance.

Question 30

Give a disadvantage to using artificial selection in bread wheat

Answer 30

Reduce genetic diversity within the species, making the species more vulnerable to coping with changing selection pressures.