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158 Biotechnology (1931) in maize. Based on their careful observation they found that some of the homologous chromosomes can be morphologically distinguished. In their investigation, two types of chromosome 9 were identified. One of the pair was a normal one whereas the other had a heterochromatic knob at one end of the chromosome and a small piece of another chromosome on the other end of it. You have already studied chromosomal aberration and understood as to how these may arise. In their experiment, two traits were used as markers to understand recombination. One was the gene that is responsible for colour of the kernel, i.e., coloured (C) versus colourless (c). The other was the gene responsible for texture of the kernel, i.e., starchy (Wx) versus waxy (wx). Performance of the cross as per Fig. 6.11 provides an evidence that during crossing over exchange of parts of homologous chromosome occur.When recombinant offspring were examined for the exchanged part of chromosome, it was found that recombinants, i.e., either coloured with starchy kernel or colourless with waxy kernel had different morphological forms of chromosome 9. Here only one of the aberrant markers were found cytologically among recombinants, contrary to the presence of both the markers on the same chromosome, establishing the fact that during recombination exchange of part of homologous chromosomes do take place. 6.4 S ex -li nked Inheritance One of the earliest known instance of sex-linked character is the bleeders disease haemophilia observed only in males in the royal family of Britain. However, the concept of sex- linked inheritance was introduced by Thomas H. Morgan in 1910, while working on Drosophila melanogaster. Morgan and his coworkers noted the sudden appearance of one white-eyed male in the culture of wild red eyed Drosophila. This white-eyed male was crossed with red eyed female, the flies of1Fgeneration (both male and female) were all red eyed, indicating that white-eyed mutation (w) is recessive to red eye colour (W). When F 1 flies mate freely, the red and white eyed flies appeared in the ratio of 3:1 in2Feneration. But all the white eyed flies were male. The red-eyed males were equally numerous. The female on the other hand were all red eyed. The white eyed female did not appear. Morgan concluded that the Reprint 2026-27