Question
Differentiate between self and cross pollination. Mention two Contrivances of each.
| Self Pollination | Cross Pollination |
| 1. It is transfer of pollen grains from an anther to the stigma of same flower or different flower in the same plant. | It is transfer of pollen grains from the anther to the stigma of a different flower a different plant. |
| 2. It occurs in bisexual flowers. | It occurs in all type of flowers. |
| 3. Pollen grains produced are less in number. | Pollen grain produced are more in number. |
| 4. It produces homezygous offsprings. | It produces heterozygous offsprings. |
| 5. The chances of variations and genetic diversity is less | It has more chances of variation and genetic diversity. |
Two Contrivances of Self Pollination :
(i) Bisexuality : Flowers should be disexual or hermophrodite so that they can self pollinate.
(ii) Cleistogamy : Some plants never open to ensure complete self-pollination. This ias called cleistogamy. The flowers which show such condition are bisexual, small, inconspcious, colourless and have no hectar. e.g., Oxalis, Viola, etc.
Two Contrivances of Cross Pollination :
(i) Diclincy of Unisexuality : Flowers should be unisexual. They can be monoecious (male and female flowers are borne on the same plant) e.g., Maize or Oecious (male and female and borne on different plants) e.g., cannabis.
(ii) Dichogamy : In bisexual flowers the ant her and stigma matures at different intervals in order to avoid self pollination and ensures cross pollination. This condition is called dichogamy e.g., coriander, Lady’s finger etc.
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| S. No. | Syndrome | Cause | Characteristics of affected individuals | SexMale/ Female/ Both |
| 1. | Down’s | Trisomy of 21 | ‘a’- (i) (ii) | ‘b’ |
| 2. | ‘c’ | XXY | Overall masculinedevelopment. | ‘d’ |
| 3. | Turner’s | 45 with XO | ‘e’- (i) (ii) | ‘f’ |