Question

Hybrids are generally superior to parents due to
A. Heterosis
B. Homozygosity
C. Heterozygosity
D. Parents are generally weak

Answer 1

Hint: The genetic composition has a direct effect on the phenotype and hence the quality of the plant. Hybrids have varied genes.

Complete answer:The hybrids are the plants that have varied genes in them. This means that they have heterozygous alleles in them. This is because hybrids are obtained by crossing the parents of the \[F1\] generation. Hybridization is done to reduce inbreeding depression or homozygosity.
Now, for the purpose of creating hybrids of superior quality, the parents are chosen from the \[F1\] generation and then crossed together. It is done artificially for the self-pollinating plants. Hence, due to the superior genes inherited from both the parents, the progeny is better at showing the phenotypic expression. This process is known as the hybrid vigour or heterosis. Thus, heterosis causes the hybrids to be generally superior to parents. Homozygosity and heterozygosity are just the conditions of the expression of the alleles and they have nothing to do with the superiority of the hybrids. Also, if the parents are weak then the offspring should also be weak.
Thus, the correct option is (A).
Additional Information: The genes have a pair of alleles in them. If both the alleles are the same, then the expression is according to both of these alleles. However, if one allele is dominant to the other, then the dominant allele will show up during the expression.
Consider the following alleles –
The \[T\] and \[t\] represent the alleles for the tallness of a plant. The \[T\] represents a dominant allele with a ‘tall’ phenotype. The \[t\] represents a recessive allele with a ‘dwarf’ phenotype. The homozygous alleles are that pair of genes in which both the alleles express the same trait. This means that either, both the alleles can be dominant or recessive. These are produced by inbreeding. It is usually seen in self-pollinating plants.
The homozygous alleles are \[TT\] represents the pair of dominant homozygous alleles, and, \[tt\] represents the pair of recessive homozygous alleles. The heterozygous alleles are that pair of genes in which both the alleles express different traits. That means that a contrasting pair of alleles are present. One gene expresses the dominant trait while the other one expresses the recessive trait. These are produced by crossing pure parents. An example of a heterozygous allele, as commonly seen by us in genetics, is as follows – \[Tt\] represents the pair of a dominant and recessive gene.

Note: The alleles are the varied form of a gene. They are located on the same position over a chromosome, known as the genetic locus. Each of the alleles of a gene are separately inherited from both the parents.