All Animals with Eyes or Eyespots That Have Been Studied

question 31

Multiple Choice

All animals with eyes or eyespots that have been studied so far share a gene in common. When mutated, the gene Pax-6 causes lack of eyes in fruit flies, tiny eyes in mice, and missing irises (and other eye parts) in humans. The sequence of Pax-6 in humans and mice is identical. There are so few sequence differences with fruit fly Pax-6 that the human/mouse version can cause eye formation in eyeless fruit flies, even though vertebrates and invertebrates last shared a common ancestor more than 500 million years ago.
-The appearance of Pax-6 in all animals with eyes can be explained in multiple ways. Based on the information above, which explanation is most likely?

• A) Pax-6 in all of these animals is not homologous; it arose independently in many different animal phyla due to intense selective pressure favoring vision.
• B) The Pax-6 gene is really not "one" gene. It is many different genes that, over evolutionary time and due to convergence, have come to have a similar nucleotide sequence and function.
• C) The Pax-6 gene was an innovation of an ancestral animal of the early Cambrian period. Animals with eyes or eyespots are descendants of this ancestor.
• D) The perfectly designed Pax-6 gene appeared instantaneously in all animals created to have eyes or eyespots.

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Definitions:

Fees Earned

Revenue generated from providing services, as opposed to selling goods, in a given period.

Prepaid Expense

An expense that has been paid in advance and will be recognized as an expense in a future accounting period.

Normal Balance

The side of an account, either debit or credit, where increases in the account are recorded.

Net Book Value

The value of an asset after accounting for depreciation or amortization, representing its carrying value on the balance sheet.