Zea mays (maize, or corn) was originally domesticated in central Mexico at least 7000 years ago from an endemic grass called teosinte. Teosinte is generally unbranched, has male and female flowers on the same branch, and has few kernels per 'cob,' each encased in a hard, leaf-like organ called a glume. In contrast, maize is highly branched, with a male inflorescence (tassel) on its central branch and female inflorescences (cobs) on axillary branches. In addition, maize cobs have many rows of kernels and soft glumes. George Beadle crossed cultivated maize and wild teosinte, which resulted in fully fertile F₁ plants. When the F₁ plants were self-fertilized, about 1 plant in every 1000 of the F₂ progeny resembled either a modern maize plant or a wild teosinte plant. What did Beadle conclude about whether the different architectures of maize and teosinte were caused by changes with a small effect in many genes or changes with a large effect in just a few genes?

In Drosophila, loss-of-function Ultrabithorax mutations result in the posterior thoracic segments differentiating into body parts with an identity normally found in the anterior thoracic segments. When the Ultrabithorax gene was cloned, it was shown to encode a transcription factor and to be expressed only in the posterior region of the thorax. Thus, Ultrabithorax acts to specify the identity of the posterior thoracic segments. Similar genes were soon discovered in other animals, including mice and humans. You have found that mice possess two closely related genes, Hoxa7 and Hoxb4, which are orthologs (see Genetic Analysis 14.2 for definition) of Ultrabithorax. You wish to know whether the two mouse genes act to specify the identity of body segments in mice.

How will you determine whether the mouse genes have redundant functions?

In land plants, there is an alternation of generations between a haploid gametophyte generation and a diploid sporophytic generation. Both generations are typically multicellular and may be free-living. The male (pollen) and female (embryo sac) gametophytes are the haploid generation of flowering plants.

How would you conduct a screen to identify genes required for male gametophyte development?

In land plants, there is an alternation of generations between a haploid gametophyte generation and a diploid sporophytic generation. Both generations are typically multicellular and may be free-living. The male (pollen) and female (embryo sac) gametophytes are the haploid generation of flowering plants.

How would you conduct a screen to identify genes required for female gametophyte development in Arabidopsis?

Which genes are the first genes that control patterning of the offspring during early development?