Q. Explain how mutating a gene which codes for receptor proteins, eventually lead to the loss od certain scents.
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So far we have discussed how limbs and body
structures and even teeth portray common descent. However it is interesting to
know that the study of scent can also be used to root back to common ancestry.
Each chemical responds to two different sets of proteins; some respond in air
and some in water. These chemicals attach to their respective protein which in
turn passes a signal to the brain there by inducing various different actions.
One such action might retrieve a memory in the brain, like the smell of a
brownie, or maybe even gasoline.
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The human nose can identify around 10,000
different odors as the 3% of our genome is constituted by receptor proteins.
However over the years due to mutations humans have lost the ability to
identify over 300 scents. The slightest change to gene can affect its ability
to sense an odor. Humans only possess
air sensing proteins and fish only have water sensing proteins. Amphibians
however possess both. Cetaceans on the other hand present another interesting
effect. Of all the thousands of scent genes, not a single one is functional in
dolphins and whales. Losing them does not affect the fitness of the organisms.
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