Question

Heterosis is
(a) Hybrid weakness
(b) Hybrid weakness and vigour
(c) Hybrid vigour
(d) Neither weakness nor vigour of Hybrid

Answer 1

Hint: Heterosis is a phenomenon exploited by both planters and breeders in which a purposeful manipulation between different plants or animals produce a new variety.

Complete answer:
Hybridisation is the method of producing new crop varieties in which two or more plants of unlike genotype are crossed where hybrid is their product. Heterosis is an outbreeding or outcrossing technique where the hybrid offspring exhibits desired and enhanced characteristics than each of their parents. Heterosis is routinely exploited by planters to produce a breed of desirable characteristics by the mating of two purebred lines with a useful trait in each of them. The increase in fitness in the crossbreds produced is known as hybrid vigour. The fitness may be in reproductive abilities, better resistance to diseases or environmental stress.
So, the correct answer is ‘ Hybrid vigour.’

Additional Information:
The first natural hybridisation was reported in corn by Mather, whereas the first artificial hybrid was obtained by Thomas Fairchild. Hybridisation can be intervarietal, interspecific and intergeneric.
- Intervarietal hybridisation is a cross between two plants of different varieties of the same species. E.g. The Maljari variety of cotton is created by the hybridisation of Malvi 8 and Jarlia.
- Interspecific or intergeneric hybridisation is the cross between two different species of the same genus. Like the Clinton, an oat is a hybrid form the cross between Avena sativa and Avena byzantina. Also, CO31 is a hybrid of rice produced from a cross between Oryza sativa and Oryza perennis.
- Intergeneric hybridisation is a cross between the plants belonging to different genera of the same family. E.g. The crop Triticale is a product of the cross between Triticale aestivum and Secale cereale.

Note:
- A pure line is a collection of plants obtained as a result of several repeated self- pollination from a single individual. Hence, a variety formed by this method displays more homozygosity or similarity in the genetic arrangement.
- One disadvantage is that new genotypes are never created by this method and thus no genetic variability which is essential for adaptations in different environmental and seasonal conditions.