Question

Linkage was discovered by
A. Blakeslee
B. Sutton
C. Muller
D. Bateson and Punnett

Answer 1

Genes are present on the chromosomes. Independent assortment of genes requires their presence on separate chromosomes. The genes present close to each other on the same chromosome exhibit linkage.

Complete answer:
The principle of independent assortment states that the alleles for a factor segregate independently of alleles for the other factors during gamete formation. Sutton and Boveri proposed the chromosomal theory of inheritance to explain the parallel behavior of chromosomes and genes during meiosis. The theory explains the principle of independent assortment. Accordingly, a pair of homologous chromosomes assort independently of the other pairs during meiosis.
However, the genes present on the same chromosomes do not assort independently. These genes are located close to each other on the same chromosome and inherit together. They are called linked genes. The tendency of the linked genes to travel together during gamete formation is called linkage.
Linkage was first observed by Bateson and Punnett during their experiment on sweet peas. They crossed the pure breeding strain of peas having purple flowers and long pollen grains with another strain exhibiting red flowers and round pollen grains. All the F1 progeny exhibited the dominant phenotype and was purple-flowered and had long pollen grains. However, the cross between two F1 plants did not obtain the progeny in 9:3:3:1. Most of the F2 progeny exhibited the parental phenotypes. It was due to the presence of genes for the flower color and the pollen length close on the same chromosome. Thomas Hunt Morgan performed dihybrid crosses on Drosophila and observed the sex-linked genes. Muller showed the use of X rays to induce mutations. Blakeslee discovered heterothallism in the Mucor species.

So, the correct answer is D. Bateson and Punnett.

Note: Although Bateson and Punnet were first to observe the linkage, they could not explain the reason for the predominance of parental phenotypes in the ${F_2}$ generation. TH Morgan coined the term “linkage” to explain the inheritance of genes located together on the sex chromosomes.