Question 1

The Kaibab squirrel lives on the north side of the Grand Canyon, and the Abert squirrel lives on the south side. Even though these two populations are only miles apart, their gene pools are kept isolated by

Accepted Answer

The Kaibab and Abert squirrels are separated by the Grand Canyon, a physical barrier, which prevents them from interbreeding, thus leading to geographic isolation.

Question 2

Temporal isolation is an example of

Accepted Answer

Temporal isolation is a premating isolating mechanism because it prevents species from mating due to differences in their mating seasons or times.

Question 3

Crossing a zebra with a horse produces sterile offspring. This is an example of

Accepted Answer

Hybrid infertility refers to the condition where offspring produced by the crossing of two different species are incapable of reproducing. This is the case with the offspring of a zebra and a horse; while they can live, they are sterile and cannot produce their own offspring.

Question 4

A horse has a diploid number (2n) of 64 and a donkey has 2n = 62. The hybrid of these two species, mules, have 2n = 63 and are sterile. Why are mules sterile?

Accepted Answer

Mules are sterile because they have an odd number of chromosomes (63), which means that during meiosis, one chromosome is left unpaired and cannot divide properly, leading to infertility.

Question 5

Two species of squirrels live on either side of the Grand Canyon. It is believed that a long time ago, before being separated by the canyon, they were the same species. This is an example of

Accepted Answer

This is an example of allopatric speciation, where a physical barrier like the Grand Canyon separates a species, leading to the evolution of new species due to geographic isolation.

Question 6

When two organisms reach sexual maturity at different times, it is an example of

Accepted Answer

Temporal isolation refers to a type of reproductive isolation where two organisms are unable to mate due to differences in the timing of their reproductive cycles. For example, one organism may reach sexual maturity in the spring while the other does so in the fall, preventing them from mating.

Question 7

Horses and donkeys can mate successfully to produce mules, which are always sterile. Which genetic isolating mechanism prevents horses and donkeys from becoming a single species?

Accepted Answer

Hybrid infertility is the genetic isolating mechanism that prevents horses and donkeys from becoming a single species, as mules, the offspring of horses and donkeys, are sterile and cannot reproduce.

Question 8

If a hybrid is unable to produce sperm because meiosis does not proceed correctly, gene flow between the species is restricted by

Accepted Answer

Hybrid infertility restricts gene flow between species because the hybrid is unable to produce viable gametes, preventing the transfer of genetic material between the parent species.

Question 9

A pet store puts both Norway rats (Rattus norvegicus) and black rats (Rattus rattus) in the same cage. If mating occurs, the pregnancy will not succeed because the embryos fail to develop properly. This is an example of

Accepted Answer

The failed development of the embryos resulting from the mating between Norway rats and black rats is an example of hybrid inviability. This means that the hybrids resulting from the mating are not viable and cannot survive to adulthood.

Question 10

When the pollen of one plant species will not germinate on the flower of another species, it is an example of

Accepted Answer

This is an example of gametic incompatibility, where the gametes of one species cannot fertilize the gametes of another species. This can lead to prezygotic isolation and prevent the production of viable hybrid offspring.

Question 11

Gametic incompatibility is an example of

Accepted Answer

Gametic incompatibility is a type of postmating isolating mechanism that prevents fertilization from occurring even if copulation has taken place. This occurs when the gametes of different species are unable to fuse and create a zygote, resulting in reproductive isolation.

Question 12

Interbreeding two different species of lovebirds produces offspring that are unable to build a nest after they mature because they lack the appropriate nest- building behavior needed to build a nest. This limits genetic mixing between the species due to

Accepted Answer

Behavioral isolation occurs when two species have differences in mating behaviors or other behaviors that prevent them from interbreeding successfully. In this case, the offspring lack the necessary behavior to build nests, which is a form of behavioral isolation.

Question 13

Where would a researcher most likely find examples of allopatric speciation?

Accepted Answer

Allopatric speciation occurs when populations are geographically isolated, leading to the evolution of new species. A mountain range with steep valleys and rivers can create such isolation.

Question 14

What happens when two populations become geographically separated from each other and then genetic divergence occurs?

Accepted Answer

Allopatric speciation occurs when two populations become geographically separated from each other and then genetic divergence occurs.

Question 15

When some hybrid organisms do not live long, it is an example of

Accepted Answer

Hybrid inviability refers to when hybrid organisms are unable to survive and develop past a certain stage, resulting in a shortened lifespan.

Question 16

The Great Dane and the Chihuahua are both domestic dogs (the same species), but mating between them is limited because of

Accepted Answer

Mechanical incompatibility refers to the physical differences that prevent successful mating between two animals, such as the significant size difference between a Great Dane and a Chihuahua.

Question 17

Lions and tigers can interbreed and produce offspring called tiglons or ligers, which have normal life spans but are sterile. Lions and tigers remain isolated genetically because of

Accepted Answer

Lions and tigers remain genetically isolated due to hybrid infertility, meaning their hybrid offspring (ligers or tiglons) are sterile and cannot reproduce, preventing gene flow between the species.

Question 18

Since the Pleistocene ice age, deserts have been gradually forming in the southwestern United States. As the original lakes and rivers of this area shrank into isolated streams, ponds, and springs, the fishes living in them developed a strong potential for

Accepted Answer

As the water bodies became isolated, fish populations were separated, leading to genetic divergence and eventually speciation due to lack of gene flow between populations.

Question 19

There are currently many similar- looking but different species on either side of the Isthmus of Panama. They most likely resulted from

Accepted Answer

The formation of the Isthmus of Panama separated marine populations, leading to allopatric speciation, where species evolve separately due to geographic isolation.

Question 20

When offspring are infertile after breeding occurs between individuals of different species, the genetic identities of the two populations are protected by

Accepted Answer

Hybrid infertility occurs when offspring resulting from the breeding of individuals from different species are sterile, thus preventing gene flow between the species and maintaining their distinct genetic identities.

Quiz 17: The Origin of Species