Gametic Isolation: Definition & Example

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  • 0:02 Hybrids
  • 0:44 Prezygotic Barriers &…
  • 2:34 Examples
  • 3:35 Lesson Summary
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Lesson Transcript
Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

Have you ever wondered why two separate species cannot mate and produce offspring? This lesson will examine the prezygotic barrier called gametic isolation and explain why interspecies cannot mate. It will also give some examples of organisms that experience gametic isolation.

Hybrids

What do ligers, zebroids, grolars, and wholphins all have in common, other than silly-sounding names? These are all hybrids, or the result of a mating of two different species, or interspecies mating. But interspecies offspring like ligers (tiger + lion), zebroids (zebra + horse), grolar (polar bear + grizzly), and wholphins (whale + dolphin) are not the norm in the world of organisms.

The term 'hybrid' can also mean the cross between different varieties within a species but for this lesson, we'll use it to mean a cross between two separate species.

Prezygotic Barriers and Gametic Isolation]

Typically, only members within a species can mate. In fact, a species is defined as a group of organisms that can interbreed or exchange genes. There are many barriers that prevent mating between different species, all of which can be divided up into two categories: prezygotic barriers and postzygotic barriers. Prezygotic barriers prevent animals from mating or, if mating occurs, prevent the sperm from fertilizing the egg. This is not to be confused with postzygotic barriers, or barriers that occur after fertilization.

Gametic isolation is a type of prezygotic barrier. Gametic isolation happens when the egg and sperm are released but a zygote is not formed. A zygote is the cell produced when an egg and sperm unite. The term 'gamete' refers to the reproductive cells like eggs and sperm.

Other prezygotic barriers prevent organisms from coming into contact with each other; they may live in different habitats, have different mating seasons, or perform different mating rituals. In cases of gametic isolation, however, the animals do come into contact, but the gametes (reproductive cells) are not compatible.

There a couple of possible reasons why the egg and sperm cannot unite in cases of gametic isolation. One is that sperm and eggs have specific proteins on their surfaces that allow the sperm to recognize the egg (and vice versa) and these proteins differ from species to species. So, if two different species mate, the sperm may be unable to recognize the egg. Another example of gametic isolation happens when the sperm is unable to survive or will be less mobile in the reproductive tract of a female from a different species.

Wow! That was a lot of vocabulary and information! Let's delve into the reproductive lives of sea urchins and coral to see gametic isolation in action.

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