Question

(a) Write the scientific name of the organism Thomas Hunt Morgan and his colleagues worked with them for their experiments. Explain the correlation between linkage and recombination with respect to genes as studied by them.
(b) How did Sturtevant explain gene mapping while working with Morgan ? [5]

Answer 1

(a) Thomas Hunt Morgan and his colleagues worked with Drosophila melanogaster for their experiments [1].

They observed that the proportion of parental gene combinations were much higher than the non-parental type in two genes in a dihybrid cross which are situated on the same chromosome. Morgan attributed this due to the physical association or linkage of the two genes and coined the term linkage to describe this physical association of genes on a chromosome and the term recombination to describe the generation of non-parental gene combinations. Even when genes were grouped on the same chromosome, some genes were very tightly linked (showed very low recombination) while others were loosely linked (showed higher recombination) [3].

(b) While working with Morgan, Alfred Sturtevant
used the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes and ‘mapped’ their position on the chromosome, thus explaining gene mapping. [1]