Reproductive isolation occurs when barriers prevent two populations from interbreeding – keeping their gene pools separate
There are two main categories of reproductive isolation barriers:
Prezygotic isolation – occurs before fertilisation can occur (no offspring are produced)
Postzygotic isolation – occurs after fertilisation (offspring are either not viable or infertile)
Prezygotic isolation barriers can be temporal, behavioural, geographic / ecological or mechanical; whereas postzygotic isolation barriers include the inviability, infertility or breakdown of hybrid organisms
Reproductive Isolation Mechanisms
reproductive isolation
Temporal Isolation
Temporal isolation occurs when two populations differ in their periods of activity or reproductive cycles
Example: Leopard frogs and wood frogs reach sexual maturity at different times in the spring and hence cannot interbreed
Behavioural Isolation
Behavioural isolation occurs when two populations exhibit different specific courtship patterns
Example: Certain populations of crickets may be morphologically identical but only respond to specific mating songs
Geographic Isolation
Geographic isolation occurs when two populations occupy different habitats or separate niches within a common region
Example: Lions and tigers occupy different habitats and do not interbreed (usually)
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4: It is a measure of how far an object moves in a certain time.
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Donor coordination is meant to counteract this and has become an important item on the international development agenda.The underlying reason for this is the growing pressure to improve the efficiency and effectiveness of development cooperation exerted, on the one hand, by the ambitious Millennium Development Goals (MDGs) and the comprehensive poverty reduction strategies being pursued by many low-income countries and, on the other hand, by scarce development cooperation resources.
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Geotropism is the influence of gravity on plant growth or movement. Simply put, this means that roots grow down and stems grow up. ... In this case, the stimulus is gravity. Upward growth of plant parts, against gravity, is called negative geotropism, and downward growth of roots is called positive geotropism.
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