02-01-2013, 12:54 PM
BACK CROSS METHOD FOR DOMINANT AND RECESSIVE GENE TRANSFER
BACK CROSS METHOD.pptx (Size: 610.73 KB / Downloads: 34)
Introduction
A cross between a hybrid and one of its parents
Suggested by Harlan and Pope(1922)
Hybrid and progenies in subsequent generation are repeatedly backcrossed to one of the parent of F1.
Objectives is to remove one or two specific defects of a HAV(high adoptable variety)
Parent involved are:
Recipient parent=recurrent parent=parent you are transferring trait to=high yielding variety
Donor parent=Non recurrent parent=genotype having desirable trait to be transferred to recipient variety(source of desirable trait)
Requirement of back cross method
A suitable recurrent parent must be available which lacks one or two character.
A suitable donor parent with high intensity of character to be transferred.
Character to be transferred should be monogenic/oligogenic with high heritability
Population requirement
10 seeds are required for monogenic trait in each back cross generation i.e. at least one plant with desirable plant should be there
Oligogenic(2or more genes) traits require large back cross population 50/100 or more to recover the recombination.
F2 and F3 generation require more plant as far as possible
Sufficient no of back cross should be made(5-6).
Dominant gene transfer
Sixth backcross generation (BC6) – Disease resistant plants are selected. They are self pollinated and harvested separately.
BC6 F2 generation – Individual plant progenies are grown from seeds of BC6 generation. Plants are selected on the basis of similarity with recurrent parent and resistance to disease. They are harvested separately.
BC6 F3 generation – Individual plant progenies are grown from seeds of above cross. As done in above step plants are selected on the basis of similarity with recurrent parent and resistance to disease but harvested in bulk.
Yield trials – Replicated yield trials are conducted with recurrent parent as a check. The newly constituted variety should be similar to variety X for most of the important characteristics. Seeds are multiplied for distribution.
Steps used for transfer of the recessive gene
Hybridization – The two varieties X and Y are crossed. Generally recipient / recurrent variety is used as female parent.
F1 generation – F1 plants are back crossed with the variety X.
BC1 generation – Plants raised from seeds of above cross are selfed. As disease resistance is controlled by recessive gene all the plants will be susceptible to disease, so disease resistance is not tested for this generation.
BC1 F2 generation – Test for disease resistance is conducted. Disease resistant plants those are similar in plant characteristic to recurrent parent are selected and back crossed with recurrent parent.