evidence of relatedness

Question 1

phylogenetic tree

Answer 1

A phylogenetic tree is a diagram that represents the evolutionary pathways leading to different species.

The axis is time, the tree branches as time moves forward.

Each junction represents the common ancestor of the organisms that branch from it. A group of branches from one common ancestor is called a clade.

The more recent the common ancestor, the more closely related the organisms are.

Question 2

biological polymers as evidence for relatedness

Answer 2

Biological polymers that have different subunits, such as DNA, RNA or protein can be used to establish relatedness. The sequences of subunits can be compared and the number of differences counted. The more differences there are in sequence, the less closely related two organisms are.

Question 3

mutations

Answer 3

Differences in sequence are owing to mutations. Mutations in DNA can lead to differences in the amino acid sequence of proteins. Depending on the organism type and reproduction rate, it is possible to use these differences to construct a “molecular clock” which shows how long ago that mutation occurred, and means that a timeline can be drawn as to when a species or group diverged.

Question 4

gel electrophoresis

Answer 4

Fragments of DNA and proteins can be separated by gel electrophoresis. The gel allows small fragments to move further and the electrical charge causes movement of the negatively charged DNA fragments to the positive electrode. A banding pattern is produced, called a DNA fingerprint, which can be used for comparison. Alternatively, sequences of DNA and amino acids can be established.

Question 5

morphology

Answer 5

Morphology means looking at the shape and form of an organism.

Question 6

morphological evidence

Answer 6

Some organisms have similar morphology but are unrelated in evolutionary terms. For example, hedgehogs, echidnas and porcupines are all similar looking and have spines for protection. This is an example of convergent evolution, and in fact the three organisms are in different orders; Echidnas are monotremes and lay eggs, Porcupines are rodents and Hedgehogs are insectivores. There are many examples of convergent evolution, where the selection pressures are similar and mutations giving rise to similar features provide an advantage. An advantage of using biochemical analysis like DNA sequencing is that it can overcome issues caused by convergent evolution.

Question 7

homologous structures

Answer 7

Homologous structures are similar structures that have different functions.

An example of a homologous structure is the pentdactyl (literally 5 fingered) limb.

The underlying structure is the same in mammals, birds, reptiles and amphibia (fish fingers are different!), but the function is different.

In birds, the forelimb is used for flight; in whales and dolphins the limb is modified for swimming, in moles for digging, in monkeys and humans for grasping.
The structure is the same even though evolution has resulted in adaptations for particular functions. Homologous structures indicate that organisms are related.

Question 8

analogous structures

Answer 8

Analogous structures arise through convergent evolution; the function is the same, however the origin of the structure is different.

A good example of this is the wings of birds and insects. In birds, the wing is a modified bony pentadactyl limb; in insects, the wing is supported by veins and has arisen from a different structure.