Evolution

Question 1

Evolution

Answer 1

A change in the genetic composition of a population during successive generations, which may result in the development of new species.

Question 2

Microevolution

Answer 2

Small-scale variation of allele frequencies within a species or population, in which the descendant is of the same taxonomic group as the ancestor.

Question 3

Macroevolution

Answer 3

The variation of allele frequencies at or above the level of species over geological time, resulting in the divergence of taxonomic groups, in which the descendant is in a different taxonomic group to the ancestor.

Question 4

Relative Dating

Answer 4

Uses index fossils (widespread, short lived fossils) by a process called biostratigraphy or correlation (this involves matching of fossils from one location to those from another). This process uses two assumptions; layers that contain the same fossil were formed at the same time in history and the lower rock layers contain older fossils than upper rock layers

Question 5

Absolute Dating

Answer 5

Uses radioactive isotopes (radiometric dating) that decay at a constant rate to form new more stable elements. Different isotopes decay at different rates and the rate of decay is measured in half-lives (the time it takes for half the quantity of an isotope to decay) e.g. some half-lives of isotopes include- C14: 5730 years, U238: 4.5billion years, K40: 1.3 billion years.

Question 6

Selection pressure

Answer 6

An external factor that acts on a population of organisms (can be biotic or abiotic)

Question 7

Natural Selection

Answer 7

Results in a change in the frequency of particular alleles within of a population over many generations due to action of a particular selection pressure which confers a selective advantage on a specific phenotype which then enhances that phenotypes (organism’s) survival and reproduction.

Question 8

Allele Frequency

Answer 8

The proportion of each allele (form of a gene) within a population (It is not the same as phenotype frequency).

Allele frequency: number of allele/ total number of alleles in population
Range of 0-1
1 means all (100%) of the population are homozygous for this allele,
0 means that none (0%) of the population have that allele.

The sum of the alternate allele frequencies (p and q) in a population should add up to 1

Question 9

Speciation

Answer 9

(formation of new species) results from some form of reproductive isolation causing a reduction in gene flow between populations.

Question 10

3 main forms of speciation:

Answer 10

Allopatric
Sympatric
Parapatric

Question 11

Allopatric Speciation

Answer 11

Where a population is separated by a physical barrier (ocean, river, mountain range, desert, deforestation) causing geographic (physical) or spatial (large distance) isolation. (is the most common form). No gene flow results

Question 12

Sympatric Speciation

Answer 12

Where organisms live in the same habitat / niche (there is no physical barrier/ geographic isolation) but don’t breed with each other (little gene flow). (This may result from behavioural or temporal isolation (eg. mismatch of breeding behaviour / season).

Question 13

Parapatric Speciation

Answer 13

Where organisms live in distinct contiguous populations that can interbreed in peripheral regions (no geographic isolation). Is low gene flow normally between individuals that live close to each other (mating is not random - with neighbours). Often multiple niches develop along a gradient as environmental factors change. Is the rarest form of speciation).

Question 14

4 Types of Macroevolution

Answer 14

Divergent Evolution- is the differentiation of distinctly different species from a common ancestral species.

Convergent Evolution- is the evolution through natural selection of similar features in unrelated groups of organisms (with no recent common ancestor). This is often due to similar selecting pressures acting on each group.

Parallel Evolution- occurs when related species that share a recent common ancestor evolve similar features independently of each other due to similar selecting pressures acting on each group.

Coevolution- occurs when two species that interact closely exert selection pressures on each other and evolve together in a reciprocal response to selection pressures.

Question 15

Divergent Evolution

Answer 15

The differentiation of distinctly different species from a common ancestral species.

Question 16

Convergent Evolution

Answer 16

The evolution through natural selection of similar features in unrelated groups of organisms (with no recent common ancestor). This is often due to similar selecting pressures acting on each group.

Question 17

Parallel Evolution

Answer 17

Occurs when related species that share a recent common ancestor evolve similar features independently of each other due to similar selecting pressures acting on each group.

Question 18

Coevolution

Answer 18

Occurs when two species that interact closely exert selection pressures on each other and evolve together in a reciprocal response to selection pressures.

Question 19

Genetic Drift

Answer 19

Random changes (not resulting from selection pressures) in allele frequencies in a population is called genetic drift. Genetic Drift is more pronounced in small populations than large populations.
E.g.: Founder effect and Bottleneck effect.
These effects often result in smaller populations with lower genetic diversity which therefore have increased risk for extinction.

Question 20

The Founder Effect

Answer 20

When a small number of a population become isolated. ‘Founder groups’ may exhibit limited variation in alleles and may not reflect the allele frequencies seen in the original population (hence, genetic drift occurs).

Question 21

The Bottleneck Effect

Answer 21

The bottleneck effect is an extreme example of genetic drift that happens when the size of a population is severely reduced. Events like natural disasters (earthquakes, floods, fires) can decimate a population, killing most individuals and leaving behind a small, random assortment of survivors.