Selection Methods Questions and Answers

Answer: C

The method useful for purifying existing varieties is Mass selection.

In mass selection, a large number of plants true to the variety's type are chosen from the population and their seed is bulked to raise the next generation, while off-types are discarded. It is simple and quick, and it is the standard method for purifying varieties that have become mixed or degenerated, and for maintaining them.

The pedigree and bulk methods are used to develop new varieties from segregating generations after a cross, and the backcross method transfers a particular gene, such as disease resistance, into an established variety.

Answer: D

The genetic variation arises mainly through Mutation.

Clonal selection is used in vegetatively propagated crops such as potato, sugarcane, banana and many fruit trees. A clone is genetically uniform because it is multiplied without sexual reproduction, so the only new heritable variation within it comes from spontaneous somatic (bud) mutations. Clonal selection picks out superior plants carrying such variation.

Segregation and recombination occur only through meiosis and fertilisation, and hybridisation is a deliberate sexual cross; none of these happens within a clone.

Answer: A

The preferred trait is erectophile leaves and compact architecture.

Erect leaves let light penetrate deeper into a dense canopy, so the lower leaves also photosynthesise instead of being shaded out. A compact plant also takes up less space and competes less with its neighbours, which is why modern high-yielding rice, wheat and maize ideotypes, such as those described by Donald, have short stature and upright leaves.

Planophile (horizontal) leaves, a sprawling habit, large drooping leaves and bushy, broad-leaved forms all capture light in the top layer and shade the rest of the canopy, which suits a sparse stand but not a dense planting.

Answer: B

The method is Speed breeding.

Speed breeding grows plants in controlled growth chambers or glasshouses under extended photoperiods of about 22 hours of light a day, with controlled temperature, so that long-day crops such as wheat, barley and chickpea flower and set seed much faster. Up to four to six generations a year can be raised instead of one or two, which shortens the time to develop a variety.

Shuttle breeding, made famous by Norman Borlaug, gains two generations a year by moving material between two field locations with different seasons, not by controlled light. Landrace enrichment and natural selection in farmers' fields do not shorten generation time at all.