Define phylogeny and explain what we can learn from phylogenetic trees

Question: Define phylogeny and explain what we can learn from phylogenetic trees.

Solution: Phylogenetics is the branch of biology that deals with the study of evolutionary histroy and relationships between a indivisuals or group of organism. Phylogeny is the diagrammatic hypothesis that helps in visualizing the history of evolutionary relationship. Phylogenetic tree helps us to understand the ancestory, the differentiating characters, how evolution has occured and also how closely are two group of organisms related.

Question: What are synapomorphies and why are they important?

Solution: Synapomorphies is a shared derived character(apomorphy ) that is present in the ancestral species and its modified form by their decendants. Synapomorphies help in identifying the closest ancestor as well as how other species have evolved from the pre existing ones. For eg the verteberal column in mammals is conserved as the number of vertebrae are mostly constant but certain elephant species have more number of vertebrae thus giving information about the closest ancestor.

Question: Differentiate between homologous and convergent characters, reversals, and homoplasies.

Solution:

Homologous characters	Convergent characters
Different function	Same function
Similar fundamental structure	Different structure
Divergent evolution	Convergent evolution
eg. four limbs in tetrapods	eg. wings of bats, birds and insects

Reversals	Homoplasies
A character in a derived state reverts back to the ancestral state	Similar traits which are not derived from a common ancestor.
Eg. leg less lizard and snakes.(loss of limbs)	eg. origin of eye.

Question:  Explain what an outgroup is and why it is important.

Solution: A group of organisms who don't belong to the group of organism whose evolutionary relationship is being studied is called the outgroup. Outgroup helps in understanding those characters which are widely distributed in the population and thus have a primitive origin.

Question: What does parsimony mean and how is it used to develop phylogenies?

Solution: In making phylogenetic tress parsimony is applied and according to it the best hypothesis is one, which requires least number of evolutionary changes. Parsimony is important in identifying the outgroup and hence making the phylogenetic tree. Parsimony also tells us how closely are two group of organisms related.

Question: Differentiate between monophyletic, paraphyletic, and polyphyletic groupings.

Solution: a) Monophyletic : Includes the most recent common ancestor and all its decendants. Eg. Mammalia and Aves.
b) Paraphyletic : Includes the most common ancestor but not all its decendants. Eg. Pisces and Reptilia.
c) Polypheletic : Does not include the common ancestor of all the taxon. Eg. Agnatha for jawless lampreys and Insectivora(anteaters and armadillos)