Question

In your own words, explain the connection between monophyly, synapomorphy, and homology. In your discussion, use limbs as a synapomorphy to tetrapods.

Answer 1

Ans:

Tetrapods: 4 limbs, neck, absence of gills, attachement of pelvic girdle to backbone

Tetrapod Synapomorphy: 4 Feet - i.e. dactylous limbs, with fingers & toes, not fins

Synapomorphies are derived traits that are shared amongst a group of organisms and are viewed as evidence of the common ancestry of the group. Synapomorphy that unites two organisms as members of the same clade the first step is to decide if the feature in question is actually the same thing in both organisms.

Synapomorphy derived in a series of lineages: a homologous trat that is shared among certain species and similar because it descended from and was modified in a common ancestor: shared, derived traits, can be used to determine the members of a clade without ambiguity for example hair is a shared derived trait i.e., synapomorphy of therians that indicates a close relationship of marsupials and placental mammals.

Five synapomorphies of chordates are:

1. Notochord- vertebrae
2. Dorsal, hollow nerve cord - becomes the spinal cord & brain (CNS)
3. Post-anal tail- gut tube exit
4. Iodine-binding structure- like thyrid
5. Pharyngeal pouches or gill slits - pouches grow laterally from anterior of the gut tube

Homology is defined as the traits inherited by two different organisms from a common ancestor. Ancestral organism shared by two or more descendent lineages i.e., an ancestor that they have in common for example, the common ancestors of two biological siblings include their parents and grandparents; the common ancestors of a coyote and a wolf include the first canine and the first mammal. A bird wing and your arm are homologous because both include bones like the humerus, radius, and ulna. However, divergent evolution related to differing functions has lead to differing outward appearance.

Monophyly originates with speciation, the two sister-species that come into being through the splitting of the ancestral species lineage forming a monophyletic taxon at the lowest level of inclusiveness. Monophyly is epistemically not accessible.