Backcross method for dominant and recessive gene transfer.

Backcross method for dominant and recessive gene transfer.

1. Backcross method for Dominant and Recessive gene transfer. PTRESEN TED BY: Pawan Nagar Reg. no.: 04-2690-2015 M.Sc.(Fruit Science)

2. Before going on the topic; What is backcross? Why backcross method is used? What is Recurrent parent and Non-recurrent parent?

3. Requirement for a backcross Programme- A suitable recurrent parent that lacks in one or two characters. A suitable Donor parent that has an intense form of character which is deficient in recurrent parent. The character to be transferred must have high heritability and governed by one or few genes. Sufficient number of backcrosses.

4. Transfer of a Dominant Gene – Suppose that a high yielding variety and widely adapted wheat variety A is susceptible to stem rust. Another variety B is resistant to stem rust and this resistance is dominant to susceptibility. Therefore, variety A is taken as Recurrent parent and variety B is used as Non-recurrent parent. Procedure is simple for dominant gene transfer than recessive gene transfer.

5. Transfer of Recessive gene – When rust resistance is due to recessive gene, all the backcross cannot be made one after the other. After the first backcross, and after every two subsequent backcrosses, F2 generations must be grown to identify rust resistant plants. The F1 and the backcross progenies are not inoculated with rust because they will be uniformly susceptible so, only the F2 populations are tested for rust resistance. Here, Variety B is rust resistance( rr ) and it is Non-recurrent parent, whereas Variety A is agronomically desirable and it is as Recurrent parent.

6. Merits of Backcross Method – The genotype of new variety is nearly identical with that of the recurrent parent, except for the gene transfer. Much smaller population is needed in this method than in pedigree method. There is the only method for inter-specific gene transfers, and for the transfer of cytoplasm. Susceptibility in a well adapted variety can be removed without affecting its performance and adaptability. Demerits – The new variety generally cannot be superior to the recurrent parent, except for the character that is transferred. Linkage drag (close linkage between a desirable and undesirable gene.) Hybridization required for each backcross; which is often difficult, time taking and costly.

7. Achievements.. Rust resistance has been transferred to Kalyan Sona from several diverse sources, eg . Robin, HS19, Bluebird etc. Tift23A was used in backcross programme with resistant lines from India and Africa to develop downy mildew resistant male sterile lines, such as MS521, MS541, etc G. herbaceum varieties Vijapla, Vijay, Digvijay and Kalyan are some of the cotton varieties developed by this method.

8. Thank you…