Variation and Evolution

Question 1

Why do organisms differ in their phenotype?

Answer 1

Different genotypes.

Same genotype different epigenetic modification Different environments.

Question 2

What is continuous variation?

Answer 2

It is controlled by a number of genes. Character shows a gradation from one extreme to another.

Question 3

Give examples of continuous variation

Answer 3

Human height, number of leaves, eye colour and body mass.

Question 4

What is discontinuous variation?

Answer 4

It’s controlled by a single gene with characters having a clear cut.

Question 5

Give examples of discontinuous variation

Answer 5

Number fingers, sex, tongue rolling ability, mammary glands

Question 6

What is heritable variation?

Answer 6

Results from genetic changes due to sexual reproduction,

Question 7

When can heritable variation occur?

Answer 7

Mixing two different parental genotypes and cross fertilisation random assortment of homologous chromosomes in metaphase I.
Crossing over between homologous chromosomes during prophase I.
Random assortment of chromatids and metaphase II.

Question 8

What do genetic changes do?

Answer 8

They establish new allele combinations only mutations generate novel and lasting variations.

Question 9

What is non-heritable variation?

Answer 9

Environmental influences that determine phenotypic variation (not inherited)

Question 10

Give examples of non inheritable variation?

Answer 10

Diet, exercise

Light, temp, availability of inorganic ions.

Question 11

Give examples of interactions between genotype and environment

Answer 11

Himalayan rabbit ears: if skin tempo falls below 25 degrees genes will produce melanin pigment, the body extremities turn on.
Hydrangae flower colour: acidic soils cause blue flowers, aluminium is more soluble at acidic pH and binds to anthocyanin pigments turning them blue.

Question 12

What limits a population?

Answer 12

Competition human and environmental factors play selective pressures on survival of different phenotypes and hence breeding success.

Question 13

What is interspecific competition?

Answer 13

Competition between individuals of DIFFERENT species i.e. predator prey relationships.

Question 14

What is intraspecific competition?

Answer 14

Competition between individuals of the SAME species basis of the origin of species by natural selection.

Question 15

What is a gene pool?

Answer 15

All the alleles, of all the genes, of all the individuals within a population at one time.

Question 16

What is allele frequency?

Answer 16

A measure of the relative frequency of an allele on a locus of a population.

Question 17

What happens to the gene pool if the environment changes?

Answer 17

Some phenotypes are more advantageous and will be selected for whilst others will be disadvantaged and selected against. Overtime the gene pool changes with some of their alleles being more frequent than others.

Question 18

What does selection pressure affect?

Answer 18

The allele frequency within a gene pool

Question 19

What is selection?

Answer 19

It is the process at which better adapted organisms are able to survive and reproduce with less adapted organisms unable to do so.

The better adapted the organism the more likely they are to pass on their characteristics to succeeding generations.

Question 20

What happens to the gene pool if the environment stays remain stable?

Answer 20

The gene pool remains stable

Question 21

What are selective agents?

Answer 21

Food supply, breeding sites, climate and human impact

Question 22

What does a selection pressure do?

Answer 22

Determines the allele frequency within a gene pool. It can affect the survival of different phenotypes in a population i.e. selective predation, camouflage, mimicry.

Only individuals who survive to reproduce are able to pass on advantageous alleles to their offspring and change the allele frequency over time.

Question 23

What are the hardy Weinberg equations?

Answer 23

p + q = 1

p^2 +2pq + q^2 = 1

Question 24

What do all the letters indicate in the hardy Weinberg principle?

Answer 24

p = frequency of allele (A)
q = frequency of allele (a)
p^2 = frequency of homozygous dominant (AA)
q^2 = frequency of the homozygous recessive (aa)
2pq = frequency of heterozygotes

Question 25

What does the hardy Weinberg principal state?

Answer 25

That the frequency of dominant and recessive alleles remain constant from one generation to the next if the following conditions are met. It only takes one generation of meeting the conditions to bring it into equilibrium this population will remain in equilibrium as long as the conditions are met.

Question 26

What are the conditions for the hardy Weinberg principle?

Answer 26

Large population – 100+ No selection for or against any phenotype Random meeting throughout the population No new mutations Population is isolated – no immigration or emigration.

Question 27

What won't occur if the conditions under which the hardy Weinberg principle applies don't change?

Answer 27

Evolution in terms of speciation

Question 28

What is natural selection?

Answer 28

When better adapted organisms survive they are able to reproduce producing successful offspring survival of the fittest.

Question 29

What are the steps in natural selection?

Answer 29

1. Variation in a population is due to mutation 2. Theres a selection pressure 3. Individuals with the advantageous alleles are more likely to survive and reproduce 4. They pass on the advantageous alleles to the next generation. 5. Over many generations the advantageous allele will become more common in a population.

Question 30

How to layout a exam question for NS:

Answer 30

Variation in ... due to RANDOM MUTATIONS in the population. These individuals have a SELECTIVE ADVANTAGE, state why.... Survive to REPRODUCE Pass on the ADVANTAGEOUS ALLELES to the next generation. Over many generations the allele frequency increases in the population (one population is no longer able to successfully reproduce with another population i.e behavioural)

Question 31

What is a population?

Answer 31

A group of organisms of the same species which reproduce with each other.

Question 32

What is genetic drift?

Answer 32

Describes how allele frequency fluctuates unpredictably from one generation to the next, reduces genetic variation. Accident and random nature.

Question 33

What is the biological species concept?

Answer 33

A group of similar individuals which are able to interbreed and produce fertile offspring and is reproductively isolated from other such groups

Question 34

What is speciation?

Answer 34

The evolution of two different species from an existing

Question 35

What is meant when a species is spectiated?

Answer 35

When two species become too genetically distinct

Question 36

When our populations reproductively isolated?

Answer 36

If there's no mixing of genes between them

Question 37

Why can speciation occur?

Answer 37

Genetic drift in isolated populations. The founder effect of disproportionate allele frequencies in small populations which can cause the equilibrium of the gene pool to change. Natural selection.

Question 38

What is the founder effect?

Answer 38

When the population is isolated on an island or new habitat the founding members of the population are a small sample of the original population. By chance they have different allele frequencies to the original population and if the population remain small it may undergo genetic drift. If the populations are genetically distinct enough they won't be able to breed and produce fertile offspring.

Question 39

What is the bottleneck?

Answer 39

It's resulting from a disaster which reduces the population size i.e. earthquakes. These populations may survive after being squeezed through a bottleneck of low numbers.

Question 40

What is alopatric isolation?

Answer 40

The formation of two spaces from an original one due to geographical isolation.The population becomes physically split into separate demes

Question 41

What are common barriers barriers to gene flow

Answer 41

rivers, mountain ranges and deserts These populations will evolve independently to each other to the environmental conditions where they live. Two populations may start to diverge and develop other mechanisms to keep them reproductively isolated, should they meet again.

Question 42

What is sympatric speciation?

Answer 42

The formation of two species from one original species due to reproductive isolation whilst occupying the same geographical location.

Question 43

What are the type of barriers?

Answer 43

``` Temporal/seasonal isolation behavioural isolation mechanical isolation gamete isolation hybrid unviability hybrid sterility ```

Question 44

What is temporal/seasonal barriers?

Answer 44

When breeding time/season or time of activity of two closely related populations don't correspond.

Question 45

What is behavioural isolation?

Answer 45

Courtship displays

Question 46

Morphological mechanical isolation is

Answer 46

Not being able to physically mate is genitals are incompatible.

Question 47

Hybrid sterility is?

Answer 47

One set of chromosomes differ from each parent so can't pair up in meiosis one and produce gametes (meiosis fails and no gametes can be produced as chromosomes in prophase one can't pair up as they aren't homologous)

Question 48

What does it mean when a plants can become polyploid?

Answer 48

The Kromozone set doubles as the chromosomes compare up in meiosis making fertile new species.

Question 49

What is hybrid unviability?

Answer 49

When fertilisation can occur but an embryo can't develop as they don't have chromosomes which match up (not homologous).

Question 50

What do all mechanisms for speciation result in?

Answer 50

A group of organisms being prevented from interbreeding, resulting in a lack of gene flow. Different selection pressures can be exerted on the group of individuals leading to a differ in allele frequency which leads to new species being created.

Question 51

What can evolution evolution be brought by?

Answer 51

Mutation, gene flow, genetic drift, natural selection

Question 52

Describe Darwin's theory?

Answer 52

Competition for limited resources and those individuals with alleles that produce a better adaptive phenotype reproduce more successfully. They pass alleles produced to the offspring which continues over generations these alleles have an increase in proportion. The average phenotype changes – evolution. If the changes are significant enough an organism may be no longer able to interbreed successfully with a representative of the original population so a new species has formed. Natural selection maintains phenotypes in a stable environment and changes them in a changing environment.