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The seedless banana, the world's most popular fruit, is losing the battle against two fungal epidemics. Why do such epidemics generally pose a greater risk to asexually propagated crops?

(a) Which Mimulus species would you categorize as mainly asexual reproducers? Why? (b) Which species would you categorize as mainly sexual reproducers? Why?

Self-fertilization, or selfing, seems to have obvious disadvantages as a reproductive 鈥渟trategy鈥� in nature, and it has even been called an 鈥渆volutionary dead end.鈥� So it is surprising that about 20% of angiosperm species primarily rely on selfing. Suggest a reason why selfing might be advantageous and yet still be an evolutionary dead end.

(a) Which species would probably fare better in response to a pathogen that infects all Mimulus species? (b) Which species would fare better if a pathogen caused hummingbird populations to dwindle?

Double fertilization means that

(A) flowers must be pollinated twice to yield fruits and seeds.

(B) every egg must receive two sperm to produce an embryo.

(C) one sperm is needed to fertilize the egg, and a second sperm is needed to fertilize the polar nuclei.

(D) every sperm has two nuclei

Compare traditional plant-breeding methods with genetic engineering.

Why does Bt maize have less fumonisin than non-GM maize

In a few species, chloroplast genes are inherited only from sperm. How might this influence efforts to prevent transgene escape?

鈥淏t maize鈥�

(A) is resistant to various herbicides, making it practical to weed rice fields with those herbicides.

(B) contains transgenes that increase vitamin A content.

(C) includes bacterial genes that produce a toxin that reduces damage from insect pests.

(D) is a 鈥渂oron (B)-tolerant鈥� transgenic variety of maize.

Which statement concerning grafting is correct?

(A) Stocks and scions refer to twigs of different species.

(B) Stocks and scions must come from unrelated species.

(C) Stocks provide root systems for grafting.

(D) Grafting creates new species.