16. A cross made between a pure breeding plant having red coloured flowers with a pure breeding plant having white coloured flowers. Such a cross is called as
(1) test cross. (2) monohybrid cross.
(3) dihybrid cross. (4) back cross.
Detailed Explanation
A cross between a pure-breeding red-flowered plant (RR) and a pure-breeding white-flowered plant (rr) differs for a single genetic trait (flower color). This meets the definition of a monohybrid cross: parents are homozygous for alternate alleles at one locus and the cross tracks inheritance of this single gene.
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All F1 offspring are heterozygous and show the dominant color.
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Selfing the F1 gives classic Mendelian 3:1 phenotypic and 1:2:1 genotypic ratios in the F2.
Why other options are wrong
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Test cross
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A test cross means crossing an individual of unknown genotype showing dominant phenotype with a recessive (homozygous) parent. Here, both parents are pure lines, not aiming to test genotype.
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Dihybrid cross
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A dihybrid cross examines segregation of two different unlinked gene traits (e.g., color and shape), requiring both parents to differ at two loci.
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Back cross
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A back cross is crossing the F1 hybrid with one of the original parents (or one genetically similar to a parent), not between two true-breeding parents of opposite types.
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Therefore, such a cross, focusing on a single character and using parents homozygous for opposite alleles, is a monohybrid cross (option 2).
