Evolution

Question 1

4.2.1 Define the terms evolution, microevolution and macroevolution

Define evolution.

Answer 1

Evolution is a change in the genetic composition of a population during successive generations, which may result in the development of new species. Evolution occurs because

• organisms produce far more offsrping than can possible survive
• many variations with an organism are controlled by genes
• natural selection keeps species adapted to their environment
• organisms have a variety of phenotypes
• new species arise by isolation of populations with different selection pressures

Question 2

4.2.1 Define the terms evolution, microevolution, and macroevolution

Define microevolution.

Answer 2

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

Question 3

4.2.1 Define the terms evolution, microevolution, and macroevolution

Define 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 descendent is in a different taxonomic group to the ancestor (kingdom, phylum, order, family, genus, species).

Question 4

4.2.2 Determine episodes of evolutionary radiation and mass extinctions from an evolutionary timescale of life on Earth.

Explain evolutionary radiation and provide two examples.

Answer 4

When random mutations in a population provide new variations, they can lead to rapid expansions in the number and diversity of taxa that can fill the available niches in the environment. The radiation can be rapid or gradual. This increases taxonomic diversity (many different forms). Adaptive radiation is a form of evolutionary radiation. It involves rapid diversification of a species into several divergent forms. Adaptive radiation is the evolutionary process by which many species originate from one species in an area and radiate to different species. It often follows the loss of another species which leaves a ‘niche’ gap in that ecosystem for other organisms to occupy. After each period of mass extinction, an episode of evolutionary radiation occurred as species evolvedto fill the niches vacated by extinct species. The phenomenon of adaptive radiation was first observed by Darwin when he travelled to a place called Galapagos Island. Another example of adpative radiation are Australian marsupials (resulting from divergent evolution - where a two or more species branch off from a common ancestor.

Question 5

4.2.3 Interpret data to reveal phylogenetic relationships with an understanding that comparative genomics involves the comparison of genomic features to provide evidence for the theory of evolution.

Describe divergent evolution.

Answer 5

Divergent evolution results in two populations of organisms that share a common ancestor but are exposed to different selection pressueres hence some differences accumalate. These differences are due to mutations in the DNA sequences that accumalate overtime. These differences may cause corresponding differences in teh amino acid sequence, and eventually in the phenotype of the organism.

Question 6

4.2.3 Interpret data to reveal phylogenetic relationships with an understanding that comparative genomics involves the comparison of genomic features to provide evidence for the theory of evolution.

What is a molecular clock?

Answer 6

A molecular clock is a technique that uses the mutation rate in a DNA sequence to deduce when two or more life forms diverged. For example 1 mutation per 1000 years. Conserved genes are less likely to accumalate mutations than other genes because they have key roles in the survivial of an organism. Any mutation may cause the organism to die, preventing the mutation from being passed on to the next generation. The molecular clock is slow in these genes. Mitochondrial DNA- mitochondria have their own circular copy of mtDNA that is inherited maternally (mother to child) with no recombination during meiosis. This means any variation is a result of accumulation of regular mutations. These genes provide a reliable molecular clock.

Question 7

4.2.3 Interpret data to reveal phylogenetic relationships with an understanding that comparative genomics involves the comparison of genomic features to provide evidence for the theory of evolution.

Explain phylogenetic trees.

Answer 7

A phylogenetic tree is a diagram that represents evolutionary relationships among organisms. Phylogenetic trees are hypotheses, not definitive facts. The pattern of branching in phylogenetic tree refelcts how species or other groups evolved from a series of common ancestors. In trees, two species are more related if they have a more recent common ancestor and less related if they have a less recent common ancestor. To generate a phylogenetic tree, scientists compare characteristics such as:
external morphology (shape/appearance)
- internal anatomy
- biochemical pathways
- DNA and protein sequences
- characteristics of fossils
Still, phylogenetic trees are hypotheses, not definitive answers Trees are revised and updated over time as new data becomes available and can be added to the analysis. This is particulalrly true today, as DNA sequencing increases teh ability to compare genes between species.