L6: Introduction to Evolution

Question 1

What is evolution?

Answer 1

Any irreversible change in the genetic composition of a population (Lomolino et al, 2010).

Or change in allele frequencies in a population.

Question 2

What is evolutionary time?

Answer 2

The period during which a population can evolve and become adapted to an environment by means of genetic change.

(Lomolino et al, 2010).

Question 3

Evidence of evolution

Answer 3

1) The sequence in which different organism appear in the geological record is strong evidence for evolution
- Fossil record (e.g shell morphology in different genera)

2) Patterns of biogeography are strong evidence for evolution: they show that each type of organisms is restricted to the part of the world in which evolved.
- Marsupials in Australia

3) Modern genetics: analyses of the structure of DNA to deduce the pattern of relationship between them and the times of their divergence from on another.
Continued isolation between these populations can gradually become so different from one another that they become new species.

(Lomolino et al, 2010).

Question 4

Darwin proposed that the diversification and adaptation of biotas resulted from…

Answer 4

natural selection. Natural selection is not synonymous with evolution. There are also other mechanisms than can cause evolution!

(Lomolino et al, 2010).

Question 5

Phylogeny

Answer 5

The evolutionary relationship between an ancestor and all of it’s known descendants (Lomolino et al, 2010)

Question 6

Darwin’s observations:

Answer 6

1) there is a huge variety of species, and species on different continents have “solved” the same problems in similar ways
2) Finch species on the Galapagos probably derived from single ancestor (possibly tiny flock), so how did they become so different?
3) when you look at individuals in a species, they usually show variation
4) most species produce more offspring than survive to breed

Question 7

Revision of mechanisms of genetic differentiation: the genetic system

Answer 7

The mechanisms that controls the characteristics of each organism and their transmission to the next generation lies within the nucleus of the cell.

Inside there are the chromosomes made of DNA.

Each characteristic of the organism is the result of the activity of a particular part of the DNA , the gene.

Each gene exists a number of different versions or alleles.

Question 8

Genotype

Answer 8

All genes that makes up the total genetic inheritance of an organism (Lomolino et al, 2010).

Question 9

Phenotype

Answer 9

The expression of the genetic message of an individual in its morphology, physiology, and behaviour (Lomolino et al, 2010).

Question 10

Evolution can also occur through random (R) processes and selection.

Answer 10

1) Natural selection
2) Mutation (R)
3) Genetic drift (R)
4) Migration or gene flow

Question 11

Natural selection

Answer 11

Change in a population that occurs because individuals express genetic traits that alter their interaction with their environment so as to enhance their survival and reproduction.

Question 12

Mutation

Answer 12

Random process. Changes in DNA.
There are 4 types: substitution of single nucleotides, deletion, insertion, or inversion of one or more nucleotides.

4 Nucleotides:
Thymine 
Cytosine 
Adenine 
Guanine

(Lomolino et al, 2010)

Question 13

Genetic drift

Answer 13

• Change in allele frequencies (genes) in a population due to chance event (random process). Non-influence of natural selection.
• More likely to occur in small population
• Unlike natural selection (favors beneficial traits) genetic drift is random. Can cause an increase of: beneficial, detrimental, or neutral traits.

Question 14

Types of genetic drift

Answer 14

Founder effect

Population bottleneck

Question 15

Founder effect

In the founder effect what does a small population size mean?

Answer 15

change in gene frequency due to colonization of a new area by a limited number of individuals.

It means this there is reduced genetic variation from the original population.

Question 16

Population bottleneck

Answer 16

Change in gene frequency due to a drastic reduction in the size of the population.

For example, a natural disaster or as a result of fragmentation or overexploitation. When a population experience a large reduction in the number of individuals, the survivors carry only a fraction if the genetic diversity that was present in the original, larger population.

Question 17

Gene flow

Answer 17

Gene flow results from dispersal. The mixing of alleles from different populations (eroding differences caused by natural selection and drifts)
Gene flow plays 2 important roles in evolution:
1) Equalizes allele frequencies (more similar)
2) Introduce new alleles into populations from other populations

• In a population of organisms, gene flow maintains an interbreeding group.
• Disruption of gene flow, physically or through a behaviour change, can isolate a population.
• Population becomes so distinct that it becomes reproductively isolated. Even if populations are rejoined, individuals no longer interbreed.

Question 18

If the following conditions are met, natural selection must occur:

Answer 18

There is variation among individuals within a population in some trait.
This variation is heritable (i.e. there is a genetic basis to the variation, such that offspring tend to resemble their parents in this trait).
Variation in this trait is associated with variation in fitness (the average net reproduction of individuals with a given genotype relative to that of individuals with other genotypes).