AP Bio prezygotic vs postzygotic barriers review

Define prezygotic barriers.

Prezygotic barriers prevent fertilization before the zygote forms.

Name the five types of prezygotic barriers.

1. Temporal isolation 2. Habitat isolation 3. Behavioral isolation 4. Mechanical isolation 5. Gametic isolation

True or False: Prezygotic barriers occur after mating.

False. Prezygotic barriers occur before mating, preventing fertilization.

What is temporal isolation?

Temporal isolation occurs when species breed at different times (e.g., seasons, times of day).

Example of habitat isolation?

Two species of garter snakes live in different habitats—one in water and the other on land.

Fill in the blank: __________ isolation prevents mating due to different mating behaviors.

Behavioral isolation.

Cause → Effect: Mechanisms of prezygotic barriers.

Cause: Different breeding times. Effect: Species do not hybridize.

What is behavioral isolation?

Behavioral isolation involves different mating rituals or signals that prevent interbreeding.

Compare mechanical isolation and gametic isolation.

Mechanical isolation: incompatible reproductive structures. Gametic isolation: sperm and egg cannot fuse.

True or False: Gametic isolation can occur even if mating happens.

True. Sperm may not be able to fertilize the egg despite mating.

Example of mechanical isolation?

Insects with incompatible reproductive organs cannot mate.

What is habitat isolation?

Habitat isolation occurs when two species occupy different environments and rarely meet.

Fill in the blank: __________ isolation arises from timing differences in reproduction.

Temporal isolation.

What is an example of temporal isolation in frogs?

Different species of frogs breed in different months.

Define gametic isolation in terms of fertilization.

Gametic isolation ensures that even if gametes meet, fertilization does not occur.

True or False: Prezygotic barriers lead to hybrid viability.

False. Prezygotic barriers prevent hybrids from forming.

What are postzygotic barriers?

Postzygotic barriers prevent hybrid offspring from developing into viable, fertile adults.

Example of hybrid inviability?

A sheep and goat can mate, but the embryo fails to develop properly.

True or False: All hybrids are sterile.

False. Some hybrids, like mules, are sterile, but not all are.

What is hybrid sterility?

It refers to hybrid offspring that develop but cannot reproduce, e.g., mules.

Fill in the blank: Hybrid breakdown occurs when __________.

the second generation of hybrids is inviable or sterile.

Difference between hybrid inviability and hybrid sterility?

Inviability occurs before birth; sterility occurs after a viable offspring is born.

Cause of hybrid breakdown?

Genetic incompatibilities in successive generations of hybrids lead to reduced fitness.

What happens during hybrid inviability?

Hybrid embryos may not develop fully, resulting in early death.

Example of hybrid sterility?

Mules (offspring of horses and donkeys) are typically sterile.

True or False: Hybrid breakdown affects only the first generation of hybrids.

True. Subsequent generations may have reduced viability or fertility.

What is an example of hybrid breakdown?

Some rice species can produce fertile hybrids, but their offspring are sterile.

Effect of hybrid sterility on populations?

Limits gene flow between species, maintaining distinct species.

How do postzygotic barriers influence evolution?

They reinforce speciation by reducing the viability and fertility of hybrid offspring.

Postzygotic barriers include which types?

- Hybrid inviability - Hybrid sterility - Hybrid breakdown

Fill in the blank: A consequence of postzygotic barriers is __________.

the reduction of gene flow between species.

What is an outcome of hybrid inviability?

The death of the embryo before it can be born.