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A species is a fixed evolutionary unit.



If two individuals from different species attempt to mate but fertilization fails to occur, this is likely the result of ________________. However, if such a mating produces a zygote that fails to form a viable embryo, this is likely the result of _______________.

pre-zygotic factors; post-zygotic factors


If an organism has a single copy of each chromosome, then it is ________.



Over a long period of time, you would expect a deleterious mutation to __________ within a large population.

decrease in frequency


Which of the following species concepts is described by a complex group of populations that are not in direct physical or reproductive contact, but do exchange genetic material through linking populations of the same species?

ring species


Consider the example of the liger cub in the above problem. The reason that lions (which live in Africa) and tigers (which live in Asia) don't produce ligers in the wild is likely the result of _________________.

ecological separation of lions and tigers


While in South America, you come across what you think are two groups of birds in the same location. They are nearly identical aside from their color. After years of observation, you conclude that the birds eat similar diets and share similar behaviors but do not reproduce with each other. These groups of birds appear to be an example of ___________

two different species on the basis of reproductive behavior


_____________ is the primary force responsible for changes in allelic frequency of deleterious mutations. _______________ is the primary force responsible for changes in allelic frequency of neutral mutations.

Natural selection; Genetic drift


___________ is a term that refers to multiple sets of chromosomes (e.g., 4, 6 or 8).



Imagine that you had two populations of red-tailed hawks―one with long tail feathers, the other with short tail feathers. Mating discrimination in this species would entail either hawks with long tail feathers preferentially mating with other hawks that have long tail feathers, or hawks with short tail feathers preferentially mating with other hawks that have short tail feathers.



You would expect similar species with a different number of chromosomes to be genetically compatible and therefore able to reproduce.



If two populations are reproductively isolated from one another (i.e., like certain populations of Russian warblers), they must be genetically isolated from each other and therefore cannot belong to the same species.



Imagine that a mad scientist wants to create a new species of minions―one that is a cross between a shark and a wolf (he plans to call them "shwolves"). To his dismay, when he introduces shark sperm and wolf eggs into a petri dish, no viable embryos form. Why?

This could be an example of pre-zygotic isolation, where the proteins of the shark sperm and wolf eggs do not interact properly; however, this could also be an example of genetic incompatibility, where genomic differences between sharks and wolves prevent the formation of viable embryos.


You observe two groups of freshwater fish that spawn at the same time of the year and in the same pond. After females lay their eggs on the pond bottom, males of both species attempt to fertilize them. After some investigation you realize that sperm from both species fertilize the eggs, but embryonic development stops shortly after fertilization when the eggs are fertilized by one species of males, but not by the other. This is an example of ______- zygotic reproductive isolation between the two species.



Speciation due to genetic drift is typically a very ____ process.



Imagine that a zoo in Sri Lanka has started an elephant-breeding program. Zookeepers have introduced an Indian and Sri Lankan elephant into the same enclosure. What will be the result of this mating?

This mating will demonstrate that these elephants are members of the same species, and will produce fertile offspring.


Which of the following represents genetic incompatibility

Two groups of snakes do not produce offspring because they have a different number of chromosomes.


Which of the following species concepts might differentiate species on the basis of descent from a common ancestor?

evolutionary species


You are an experienced naturalist and biologist and you observe two birds mating that you do not believe to belong to the same species. The eggs from this breeding do not hatch, and when you obtain one of the eggs, you find embryonic development stopped not long after fertilization. Which of the following conclusions is supported by these observations?

Post-zygotic factors prevented successful reproduction.


Which of the following statements is true regarding a genus?

A genus is composed of "similar" species, although this grouping can be subjective.


A population of rare frogs is reduced by 90% in number when a large dam is constructed that obliterates most of their prior habitat. Which of the following is probably true?

The reduced genetic diversity of the remaining frogs makes genetic drift more likely.


Which of the following statements is true regarding the biological species concept?

Given the generation time of certain organisms, the biological species concept can be difficult to test.


Which of the following species concepts might differentiate species on the basis of specific dietary requirements?

ecology species


Which of the following is true regarding sympatric speciation?

Sympatric speciation requires a selective disadvantage of hybrids (e.g., medium-billed birds) of two diverging populations.


True or false: Some cases of hybridization that lead to instantaneous speciation result in alteration of chromosomal number



A rule of thumb known as the morphospecies concept holds that:

morphology is generally consistent within a species