(i) What are the characteristic feautures of a true-breeding line? |
(ii) In peas, tallness is dominant over dwarfhess, and red colour of flowers is dominant over the white colour. When a tall plant bearing red flowers was pollinated by a dwarf plant bearing white flowers, the different phenotypic groups were obtained in the progeny in numbers mentioned against them. |
Tall, Red =138 |
Tall, White =132 |
Dwarf, Red =136 |
Dwarf, White =128 |
Mention the genotypes of the two parents and of the types of four off springs. |
Answer:
(i) A true-breeding line for a trait is one that, has undergone continuous self-pollination or brother-sister mating, showing a stability in the inheritance of the trait for several generations.
(ii) The result shows that the four types of offspring are in a ratio of 1 : 1: 1: 1. Such a result is observed in a test-cross progeny of a dihybrid cross.
The cross can be represented as:
Tall & Red \[\times \] Dwarf & White
(Tt Rr) (ttrr)
TR Tr \[\times \] tr
tR tr
tr
TR
TrRr
Tall Red
Tr
Ttee
Tall White
tR
TtRr
Dwarf Red
tr
ttrr
Dwarf white
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