In some regions the rainfall is becoming less reliable, and crops may fail when the soil becomes too dry. To help, scientists have produced genetically modi...

This question covers genetic engineering and a monohybrid (one-gene) cross.

(a) [2] Genetic engineering is the changing of the genetic material (DNA) of an organism [1] by inserting a gene from a different organism into it [1].

(b) [4] The steps used to move the drought-tolerance gene into a maize cell, one mark each:

1. The required gene is cut out of the donor organism's DNA using a restriction enzyme [1].
2. The gene is joined (spliced) into a vector such as a plasmid or Agrobacterium using the enzyme ligase [1].
3. The vector carries the gene into the maize cell [1].
4. The transformed cell is grown (cultured) into a whole maize plant, every cell of which now contains the gene [1].

(c) [3] The crop can grow and survive using less water [1]; so it gives a more reliable and higher yield in dry conditions [1]; meaning more food and income for the farmer and less crop failure [1].

(d) [2] Any two possible risks: the inserted gene may spread to wild/related plants; a fall in biodiversity; unknown effects on other organisms or on human health [2, 1 each].

(e) [2] Complete the cross \(Dd \times dd\). Each parent passes one allele to each offspring, so combine the mother's gametes (D and d) with the father's gametes (d and d):

The four offspring are \(2\ Dd : 2\ dd\), that is one half each. Because D is dominant, one copy is enough to give tolerance, so 50% (one half) of the offspring are drought-tolerant [1], and their genotype is Dd (heterozygous) [1].

(f) [2] The non-tolerant offspring have genotype dd, so they lack the tolerance gene/protein [1]; in dry conditions they lose too much water and wilt or cannot grow, so they survive less well [1].