BOTANY Higher Secondary Second Year - Textbooks Online

3.4. Recombination of chromosome
The process, which produces recombinations of gene by interchanging
of corresponding segments between nonsister chromatids of homologous
chromosomes, is called recombination of chromosomes. It takes place in
pachytene stage of prophase I of meiosis. Crossing between the linked
genes results in genetic recombination.
According to Bateson and Punnet, in Lathyrus odoratus 12 per cent
of the test cross progeny were recombinants. Recombination between two
genes is expressed in percentage. It is called recombination frequency.
Gene pairs that had very low percentage of recombination are known as
tightly linked genes. The gene pairs with higher percentage are termed as
loosely linked genes. For example, 12 per cent of the test cross progeny
were recombinants. They showed a different linkage of alleles than their
parents. The percentage recombination is determined by dividing the
number of recombinant offspring by the total number of offspring. In the
figure 3.4, the linkages of the parents were B with L and b with l. The
recombinant offspring are B with l or b with L.
Self evaluation
I . Choose and write the correct options.
1. Recombination of chromosome takes place in _____ stage of
prophase I of meiosis.
a. leptotene b. zygotene
c. pachytene d. diplotene
II. Answer the following questions in two or three sentences.
2. What are tightly linked genes?
3. What are loosely linked genes?
III. Answer the following questions in about 100 words.
4. Write short notes on Recombination of chromosomes.
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