What is the prezygotic barrier
The prezygotic isolation mechanisms prevent fertilization or even mating of two different individuals. A distinction is made there between different variants.
Mechanical / physiological isolation
Individuals have developed different sexual organs. As a result, copulation does not occur and the fertilization of the egg cell has been prevented (often with insects / molluscs).
There is a different temporal sequence in the maturation of egg cells, which have to be fertilized at a certain point in time. The mating season of the individuals who want to reproduce differs and there is no mating. The same applies to plants and their flowering times.
This type of isolation is related to the behavior of individuals. There are behavioral differences. This can be, for example, a different behavior when looking for a pair.
One species of bird has different courtship calls or courtship behavior than the other bird species.
Courtship = Behavior before mating in order to find reproductive partners
Looking for individuals different ecological niches on. This allows them to live in the same habitat as other individuals and to meet them, but mating does not occur.
For example, one species uses the available resources and environmental conditions differently than the other species in the same habitat (squirrels / flying squirrels). The consequences can be different times of activity or mating times, but also looking for different foods to survive.
Ecological niche = Totality of the interrelationships between a living being and its environment
Become individuals spatially separated. Seas, mountains or valleys mean that the individuals do not meet and thus cannot reproduce with one another. If an individual lives only in the sea (fish) it is spatially separated from individuals who only live in the air (bird).
If you learn more about geographic isolation and the Consequences of such a separation want to know, then you can read about this in the text on allopatric speciation.
And now we come to the postzygotic isolation mechanisms.
The postzygotic isolation mechanisms are mechanisms that work after the egg cell has been fertilized and thereby prevent the growth of fertile or viable offspring.
As a rule, the further development of the zygote is prevented.
zygote = Cell after the fusion of the egg cell and sperm cell (state after fertilization)
The postzygotic isolation mechanisms are also a type of genetic isolation. We come to the consequences of postzygotic isolation.
Usually there is a certain sequence of steps until the mating of two individuals results in an offspring. The postzygotic isolation mechanisms prevent these Embryonic development steps. As a result, they cannot proceed properly.
The egg cell is fertilized and the zygote arises from it, but from now on it will not develop any further. It comes to no viable offspring.
The process of mating up to fertilization and the birth of an offspring is not prevented here.
However, the descendant can now one higher risk of illness have or barren be. Also, a consequence of the effect of the postzygotic isolation mechanisms can lead to the offspring having a increased likelihood of dying soon after birth becomes.
A horse and a donkey can have offspring in common. These offspring are called mules, but are not themselves capable of reproduction. Mules remain even without offspring. In addition, the risk of miscarriage is relatively high when a horse and donkey are crossed.
In this learning text you have learned everything about isolation and the pre-zygotic and post-zygotic isolation mechanisms. In the Exercises you can now apply and test your newly acquired knowledge. We wish you a lot success!
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