The molecular clock refers to mutations in DNA nucleotide sequence of genes occurring at a constant rate over time. The greater the difference in nucleotide sequence between two individuals of different species, the greater the amount of time has passed since they diverged from a common ancestor. The molecular clock helps to provide evidence to support conclusions previously based on comparative morphology and fossil records. Hypothesis:
One hypothesis is that arthropods evolved more recently from an annelid like ancestor then a nematode ancestor because of their similar body plan and segmentation. The other hypothesis is that arthropods evolved more recently from a nematode ancestor than an annelid like ancestor because of their shared ecdysis trait. Hypothesis 1
The morphological data that supports hypothesis one is that annelids and arthropods both have segmented bodies, dorsal circulatory systems, ventral nervous systems, and appendages. The morphological data that supports hypothesis 2 is that nematodes and arthropods have a nonliving cuticle around their body and undergo ecdysis and molting. Procedure:
Cytochrome-c oxidase is the amino acid sequence of a protein that is an essential component of the electron transport chain in aerobic respiration. Therefore it is present in all aerobic organisms and is a good tool to help with molecular phylogenetic studies. Each student in class was given certain organisms and they had to compare the organisms’ cytochrome-c oxidase sequences to look for differences in the sequences of amino acids. The students counted the number of differences in the amino acid sequences they were comparing and reported their findings to the professor. The professor then took the average of the differences in each comparison to compile a data sheet of the results for the students to use....
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