Question

1. A part of the aminoacid sequence in Cytochrome-C protein from 6 different species is given in the table. Rank the organisms from 1 to 5 according to the similarity of the organism to human: based on the similarity between the cytochrome C aminoacid sequences, 1 being the closest to human. It is largely agreed that the greater the number of amino acid (or nucleotide) differences between a given pair of organisms, the further apart they are in evolution. On the other hand, if two organisms show very few differences, they are likely to be closely related. With the given information in the table and your ranking of organisms, do you think this ranking gives definite information on how further apart the organisms are in evolution? Why/why not?
2. Human - DVEKGKKIFIM
3. Silkworm moth - NAENGKKIFVQ
4. Chicken - DIEKGKKIFVQ
5. Rhesus monkey - DVEKGKKIFIM
6. Bullfrog - DVEKGKKIFVQ
7. Tuna - DVAKGKKTFVQ

Answer 1

The comparison should consider which amino acids coincide (in identity and position) and which do not. It yields:

• Silkworm moth: aa that: coincide: 6, not coincidence: 5
• Chicken: aa that: coincide: 8, not coincide: 3
• Rhesus monkey: aa that: coincide: 11, not coincide: 0
• Bullfrog: aa that: coincide: 9, not coincide: 2
• Tuna: aa that: coincide: 7, not coincide: 4

The order would be:

1. Rhesus monkey
2. Bullfrog
3. Chicken
4. Tuna
5. Silkworm moth

No, this is not definitive. This ranking is based on a part of the sequence of one amino acid, which does not make it representative of the whole genome of the species involved. We would need many more of these comparisons to make a ranking that gives definitive information on how further apart the organisms separated in an evolutionary timeline.