Chapter 10 - Variation and Evolution.

Question 1

Why do organisms differ in their phenotypes?

Answer 1

• They have a different genotype.

- They have different environments.

Question 2

What does it mean if a characteristic is heritable?

Answer 2

If they result from different DNA nucleotide sequences or, in some cases, different epigenetic modification, they can be inherited.

Question 3

How does sexual reproduction generate heritable variation?

Answer 3

• Crossing over between homologous chromosomes during prophase I of meiosis.
• The random distribution of chromosomes during metaphase I.
• The random distribution of chromatids at metaphase II.
• The mixing of 2 different parental genotypes at fertilisation.

Question 4

What does it mean if a variation is non-heritable?

Answer 4

If the variation is imposed by the environment that isn’t a result of epigenetic change and cannot be transmitted to offspring.

Question 5

What are the 2 types of variation?

Answer 5

• Discontinuous.

- Continuous.

Question 6

What is discontinuous variation?

Answer 6

For some characteristics, there is only a small number of possibilities. There are no intermediates and the characteristics are discrete. These characteristics are controlled by single genes and so are monogenic.

Question 7

What is continuous variation?

Answer 7

-For some characteristics, there are many possible values e.g. height. The values show a gradation from one extreme to another. These are controlled by many genes and are described as polygenic. The environment has considerable influence on the phenotypes.

Question 8

What are the 2 types of competition?

Answer 8

• Inter specific competition, between individuals of different species.
• Intra specific competition, between individuals of the same species.

Question 9

What is selection pressure?

Answer 9

An environmental factor that can alter the frequency of alleles in a population, when it’s limiting.

Question 10

What is the gene pool?

Answer 10

All the alleles present in a population at a given time.

Question 11

What is the allele frequency?

Answer 11

The frequency of an allele is its proportion, fraction or percentage of all the alleles of that gene in a gene pool.

Question 12

What is genetic drift?

Answer 12

Chance variations in allele frequencies in a population.

Question 13

What are the three factors which can cause significant changes to the allele frequency of a gene pool?

Answer 13

• Mutation.
• Natural selection.
• Genetic drift.

Question 14

What does the Hardy-Weinberg principle state?

Answer 14

That in ideal conditions, allele and genotype frequencies in a population are constant from generation to generation.

Question 15

What is meant by the term evolution?

Answer 15

Allele frequencies change and phenotypes alter over time.

Question 16

What is speciation?

Answer 16

The formation of a new species. If the change in phenotype is profound enough, organisms with the altered phenotype are unable to reproduce successfully with the initial population.

Question 17

What is the founder effect?

Answer 17

The loss of genetic variation in a new population established by a very small number of individuals from a larger population.

Question 18

What are the 3 types of natural selection?

Answer 18

• Stabilising selection.
• Directional selection.
• Disruptive selection.

Question 19

What is the concept of stabilising selection?

Answer 19

In a stable environment, the average phenotype may provide a greater advantage than either extreme. In this case, the extreme values will be selected against.

Question 20

What is the concept of directional selection?

Answer 20

In a changing environment, an extreme phenotype may become advantageous. Then, other values are selected against and over time, the average phenotype changes.

Question 21

What is the concept of disruptive selection?

Answer 21

In some situations, the average phenotype doesn’t provide an advantage and is selected against (The extremes are selected for at the same time). If these two demes are isolated, a new species may occur.

Question 22

What is a species?

Answer 22

A group of phenotypically similar organisms that can interbreed to produce fertile offspring.

Question 23

What is reproductive isolation?

Answer 23

The prevention of reproduction and, therefore, gene flow between breeding groups within a species.

Question 24

What are the 2 forms of reproductive isolation?

Answer 24

• Pre-zygotic, gametes are prevented from fusing so a zygote is never formed.
• Post-zygotic, gametes fuse and zygote forms but is sterile and so the genes of the parent species are kept separate.

Question 25

What is the difference between Allopatric speciation and Sympatric speciation?

Answer 25

• Allopatric, the evolution of a new species from demes isolated in different geographical locations (Physically split).
• Sympatric, the evolution of a new species from demes sharing a geographical location (The barriers are not physical ones).

Question 26

What are the examples of sympatric speciation?

Answer 26

• Morphological isolation.
• Behavioural isolation.
• Gametic isolation.
• Seasonal isolation.
• Hybrid inviability.
• Hybrid sterility.

Question 27

What is the concept of seasonal isolation?

Answer 27

Reproductive organs of different demes are mature at different times of the year. They are therefore unable to hybridise and are genetically isolated.

Question 28

What is the concept of Geographical isolation?

Answer 28

Occurs when the population becomes split by a physical barrier into separate demes. the physical barrier may be a mountain, a river, desert or other features that prevent interbreeding.

Question 29

What is the concept of behavioural isolation?

Answer 29

Many animals have mating rituals and courtship displays that are recognised by other members of the same species as a prelude to mating.

Question 30

What is the concept of morphological/mechanical isolation?

Answer 30

This is caused by variation in the sexual organs which can lead to some being unable to mate successfully with one another.

Question 31

What is the concept of Gametic isolation?

Answer 31

Gametes in open environments often meet gametes of other species e.g. in coral reefs,. In about 2/3 of the cases, they’re incompatible. Barriers prevent the fusion of gametes of different species, so populations are isolated.

Question 32

What is the concept of hybrid inviability and sterility?

Answer 32

• Inviability, fertilisation occurs but incompatibility between the genes of the parents prevents the development of the embryo.
• Sterility, an embryo formed from the gametes of 2 species can develop but if the chromosomes are not sufficiently similar, they are unable to pair at prophase I of meiosis and so gametes can’t form meaning the hybrid is sterile (Odd number of homologous chromosomes).

Question 33

What are the changes in a population brought about by?

Answer 33

• Mutation.
• Gene flow.
• Genetic drift.
• Natural selection.

Question 34

Why are low levels of antibiotics left in the environment?

Answer 34

• They have been added routinely to animal feeds in intensive farming.
• They have been added to handwashes.
• People may not finish a prescribed course.

Question 35

Why does some bacteria develop antibiotic resistance?

Answer 35

Bacteria reproduce rapidly and therefore random mutation quickly led to resistant strains.

Question 36

How does a gene for resistance in a species quickly spread to others?

Answer 36

Bacteria can pass plasmids on during binary fision and directly to any other bacterial cell by means of a pilis.