Question

Consider two unlinked genes P and Q. A plant with genotype PPQQ was crossed with another plant with genotype ppqq to obtain F1 progeny. If the F1 progeny to test-crossed, the percentage of resultant plants with the genotype ppqq will be:
$$\begin{gathered} A.50\mathrm{\%} \\ B.25\mathrm{\%} \\ C.100\mathrm{\%} \\ D.10\mathrm{\%} \end{gathered}$$

Answer 1

Hint:When genes are found on different chromosomes or far apart on the same chromosome are said to be unlinked. The genes that are close together on the same chromosome, they are said to be linked.
The genotype is a complete set of heritable genes or the genes that can be passed down from parents to offspring.

Complete answer:
The cross between F1 progeny with homozygous recessive parents.
On test cross, the resultant genotypes are PpQq, Ppqq, ppQq, ppqq in the ratio $1:1:1:1$.
Hence percentage of resultant plants with the genotype ppqq will be $\to {\displaystyle \frac{1}{4}}\times 100=25\mathrm{\%}$

$i.e{\displaystyle \frac{1}{4}}\times 100=25\mathrm{\%}$

Hence B $25\mathrm{\%}$ is the correct option.

Note: Phenotypic ratio pertains to the relative number of offspring manifesting a particular trait or combination of traits. The genotypic ratios produce characteristic phenotypic ratios, according to the dominance relationships of the alleles involved.