41.   The theory is that sterile insects mate with their wild counterparts but produce no offspring.

42.   Then the transgenic and knockout mice were bred, eventually producing offspring that had all their mouse hemoglobin genes replaced by the mutant human ones.

43.   These females could produce YY males, which would then be capable only of producing male offspring, upsetting the sex balance in a fish population.

44.   These strings can be combined and mutated to produce offspring whose fitness is then evaluated.

45.   This easy-to-grow plant spreads and produces numerous offspring from seed.

46.   Top broodmares have always sold for less, because they produce fewer offspring.

47.   Until a few centuries ago in Western culture, marriage was primarily an economic institution that ensured inheritance rights, protected political arrangements and produced offspring.

48.   Webs are especially important to female spiders, who must catch enough protein to produce offspring.

49.   West said that if this process could be used to produce live offspring it would open up vast new reproductive possibilities.

50.   Would only the desire to produce offspring be sufficient to maintain the species?