Question

A cross between a true-breeding sharp-spined cactus and a spineless cactus would produce?

1) all sharp-spined progeny
2) 50
3) 25
4) all spineless progeny
5) It is impossible to determine the phenotypes of the progeny

Answer 1

Assuming Mendelian genetics and dominance of the sharp-spined trait, a cross between a true-breeding sharp-spined cactus and a spineless cactus should produce all sharp-spined progeny.

Step-by-step explanation:

The question pertains to the principles of genetic inheritance, specifically when crossing two cacti with different phenotypes: one having sharp spines and the other being spineless. Applying Mendel's laws of inheritance, if the sharp-spined trait is dominant, and these cacti remain true to classic Mendelian genetics, then all sharp-spined progeny would be expected (option 1), assuming that the sharp-spine trait is completely dominant over the spineless trait.

However, without information on whether the sharp-spined trait is dominant or not, and if this species follows simple Mendelian inheritance, it would be impossible to determine the phenotypes of the progeny for certain (option 5). The assumption would need to be confirmed by the results of the cross or by existing knowledge of the genetic basis for spines in cacti.