Question

Mendel studied 7 pea- plant characters. Why was he unable to spot linkage in any of the genes?

• A. The genes were located on 7 different chromosomes
• B. The genes were located sufficiently far apart on the chromosomes
• C. Pea plant doesn’t have any linkage group
• D. Mendelian traits are discrete

Answer 1

The correct option is B The genes were located sufficiently far apart on the chromosomes

Mendel chose to study seven characters of the pea plant. The genes of these seven characters under study were located on four different chromosomes. Genes of three characters were located on chromosome 4 and for two other characters were located on chromosome 1. Chromosomes 5 and 7 had one gene each.
Though some of the genes were located on the same chromosome, they did not show any linkage. It is most probably because they were located sufficiently far away from each other and behaved as independent units (they were inherited independent of each other).
Another probable reason could be, Mendel never made appropriate crosses, i.e. he never took into account the characters which were located on the same chromosome for his experimental crosses. So, he could not report linkage.
For a pea plant, its diploid number is 14. The number of linkage groups would be its haploid number i.e. 7.
It is true that Mendelian traits are discrete. Discrete traits are the ones which are controlled by a few genes, most preferably one. And they usually have only 2 alleles. These are also known as discontinuous alleles. But this is not a sufficient reason for why linkage was not reported in pea plants.