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In the oceans on either side of the Isthmus of Panama are 30 species of snapping shrimp, 15 species on the Pacific side and 15 different species on the Atlantic side. Species live at different water depths. Morphological and genetic data show that Atlantic and Pacific species that live at similar depths are sister species. Geological evidence indicates that the Isthmus of Panama started rising about 10 million years ago and the oceans were completely separated by the isthmus about 3 million years ago. If the isthmus indeed formed gradually, which of the following patterns of genetic differences is most likely in these species pairs?
A) similar percentages of difference in DNA sequences between all pairs of sister species
B) greater percentage of difference in DNA sequences between sister species that inhabit deep water than between sister species that inhabit shallow water
C) greater percentage of difference in DNA sequences between sister species that inhabit shallow water than between sister species that inhabit deep water
D) greater percentage of difference in DNA sequences among Atlantic species than among Pacific species

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Answer:

B) greater percentage of difference in DNA sequences between sister species that inhabit deep water than between sister species that inhabit shallow water

Explanation:

The isthmus formed gradually. About 10 million years ago, the isthmus began to separate the waters from the bottom, and snapping shrimp individuals inhabiting the deepness were separated for the first time. Since their separation, both groups evolved according to their new environment and the pressures acting on them. They started to gradually differentiate from each other, probably suffering many mutations through the years.

About 3 million years ago, the oceans were completely separated by the isthmus, meaning that those animals inhabiting the shallowest areas were the last ones to separate from each other on each side of the isthmus. Since then, they probably also suffered many mutations that drove them to differentiation.  

However, as animals inhabiting the shallowest areas were the last ones to separate and, considering the time-lapse between both divergences, the highest degree of genetic difference is expressed by the sister groups inhabiting the deepest areas. Being separated from each other for a much longer time than shallow animals gave them more time to suffer more mutations and differentiate more.

The sister species at the depth of the ocean possesses a greater difference as compared to the sister species in shallow regions. Thus, option B is correct.

Evolution is the process of inheritable changes in the species with natural selection. The species in the close generation have a higher level of similarity in the traits.

What is the relation between the sister species?

The sister species are the ones with the similarity in the traits. Thus, have the same ancestors and exhibit a greater percentage of trait similarity.

Atlantic and Pacific species are sister species and have similarities in the DNA sequence.

The isthmus separation is formed later in the ocean. The species present at the deeper range are older and are evolved. The species in the shallow region have less evolution as they are separated later.

Thus, the sister species at the depth of the ocean possesses a greater difference as compared to the sister species in shallow regions. Thus, option B is correct.

Learn more about evolution, here:

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