unisexuality , Dichogamy , Prepotency , Heterostyly , Herkogamy , self incompatibility explain with definition.
Answers
Introduction
The transfer of pollen grains from the anther of one flower to the stigma of the same or different flower is called as pollination. Pollination can be of two types:
Self-Pollination– The transfer of pollen grains from the anther of one plant to the stigma of the same plant.
Cross- Pollination– The transfer of pollen grains from the anther of one plant to the stigma of a different plant.
Self-pollination is also called as inbreeding whereas cross-pollination is known as outbreeding.
Reasons for Outbreeding
Continued inbreeding or self- fertilization leads to a condition called as inbreeding depression. This condition is characterized by homozygous genes which are not as vital as they need to be leading to unhealthy offsprings.
In self- pollination, since both the male and female gametes share the same genes, there is no genetic variation seen which is necessary for a better, more productive offspring. So, most plants have many mechanisms that they employ to avoid self -pollination and promote cross-pollination.
Outbreeding Devices
Plants have many mechanisms and devices that they employ to promote cross-pollination. Let us look at a few of them in the following segments:
Unisexuality: In this case, the plant bears either male or female flowers and is not hermaphrodite. It is also called as Dioecism.
Dichogamy: In this mechanism, the stigma and anther mature at different times. Depending on who matures first, dichogamy can be further divided into two:
Protandry: In this type, the androecium matures earlier than the gynoecium. Ex: maize plant
Protogyny: In this type, the gynoecium matures earlier than the androecium.
- Herkogamy: This is a name given to a condition where there is a natural physical barrier that prevents the pollen of the same flower from entering the ovary.
Self- Sterility: In this condition, there is a gene that recognizes the similar gene and does not allow the pollen grain to germinate. This is due to the self-sterile gene present in the ovule and the grain.
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