312 Geckos No limbs ANCESTRAL LIZARD (with limbs) 260 Snakes 189 Iguanas 72 111M
ID: 253215 • Letter: 3
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312 Geckos No limbs ANCESTRAL LIZARD (with limbs) 260 Snakes 189 Iguanas 72 111Monitor lizard 85 108 Eastern glass lizard No limbs Q7. You discover a fossil of the ancestor of all living lizards and estimate that it is 350 million years old. The numbers above each lineage in your lizard cladogram denote the number of nucleotide changes per 10,000 base pairs in the 16S tRNA gene. (3 pts) a. What are some things you can assume about the 16S rRNA gene? (1 pt) Many snakes and monitor lizards are venomous. What would vou need to know to be able to decide whether this is a case of homology or analogy? (1 pt) b. Based on only what is depicted in this cladogram, what is the most parsimonious explanation for the presence of venom in snakes and monitor lizards assuming none of the other taxa are venomous? Why? (1 pt) c.Explanation / Answer
Answer a.
The things which can be assumed about 16SrRNA are:
1.16S rRNA is present in all species, whether it was existing 350mya or now.
2. Second, change in 16SrRNA, can result in marked changes in gene expression. This can change development pattern also. Morphogens produced during developed can also be changed.
3. The morphogens required for limb development are affected by 16SrRNA.
Answer b.
It is given that many snakes and monitor lizards are venomous. If this characteristic was an analogy then it would be present in all the given five animals. But, this is not the case. The characteristic is present only in two animals, i.e. snake and monitor lizard. So, the character is homologous.
Note: homologous characteristics can be ancestral (sym-plesiomorphic) or derived (syn-apomorphic).
Answer c.
Fewest evolutionary changes should have occurred in an organism to be most parsimonious.
Monitor lizard and snakes, both belong to the same monophyletic group. As per this diagram, you can say that having stripes on their bodies in similarities in 16S rRNA make these two animals most parsimonious.
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