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Postzygotic Reproductive Barriers: Definition & Examples

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  • 0:06 Prezygotic and…
  • 1:48 Hybrid Zygote Abnormality
  • 2:44 Hybrid Infertility
  • 4:40 Low Hybrid Viability
  • 6:06 Lesson Summary
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Lesson Transcript
Instructor: Greg Chin
Do flying hamsters represent a separate species from your run-of-the-mill hamsters? We'll get to the bottom of this by performing crosses between the two hamster types. You'll explore postzygotic reproductive barriers and their possibly tragic consequences.

Prezygotic and Postzygotic Isolation

Well, while we were waiting for our run-of-the-mill hamsters to show up, we learned a lot about the types of barriers that can cause reproductive isolation at a point before fertilization. Matings between our flying and non-flying hamsters successfully result in fertilization and zygote formation. Therefore, it doesn't seem like the gene pools of the two types of hamsters are isolated prezygotically. However, even if the two types of hamsters were able to mate and produce a zygote, that zygote still has to successfully mature to a reproductive age and produce progeny for the two hamsters to be simply variants of the same species.

Although prezygotic barriers may not have caused speciation, a mechanism that occurs after zygote formation could still be isolating the gene pools of the two populations of hamsters. Postzygotic reproductive barriers occur after the zygote has formed, meaning they either reduce the viability (which basically means the ability to avoid dying) or the reproductive capacity of the hybrid offspring. Hybrid zygote abnormality, hybrid infertility, and low hybrid viability are postzygotic mechanisms that could still define the flying hamsters as a different species than non-flying hamsters. Let's examine these possibilities more closely to see if our flying hamster is a new species.

Hybrid Zygote Abnormality

Although fertilization may succeed, the hybrid zygote still has to develop and mature into an adult organism. Sometimes hybrid zygotes fail to mature normally. This is referred to as hybrid zygote abnormality. Normally, this means that the hybrid dies during development, but sometimes the hybrid survives birth yet suffers from such severe abnormalities that it can't successfully mate as an adult. Well, it looks like early development of our hybrid hamsters progressed normally. The hybrids survived birth and appear to be growing normally, albeit a little bit small. So it looks like we can cross off hybrid zygote abnormality as a possible mechanism of speciation dividing the flying and non-flying hamsters.

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