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The carpel contains one or more ovules; these contains megasporangia protected by two layers of integument cells. The megasporangia divide meiotically to produce haploid megaspores, All of the carpel is diploid except for the megaspores, which divide mitotically to produce the embryo sac (the female gametophyte).

Phenotypes of mice with mutations along the pigment cascade. The Steel and White mice have mutations in the genes for stem cell factor (ligand) and c-kit protein (receptor), respectively. These proteins activate the Mitf transcription factor through the pathway shown in Figure 6.15. Mitf mutations give rise to the microphthalmia phenotype, which contains a subset of those anomalies seen upstream in the pathway. The albino mutation is farther down on the pathway and contains a subset of those conditions found in the Mitf mutants.

Inheritance patterns for Prader-Willi and Angelman syndrome. The region in the long arm of chromosome 15 contains the genes whose absence causes these syndromes. However, they are imprinted in reverse fashion. In Prader-Willi syndrome, the paternal genes are active, while in Angelman syndrome, the maternal genes are active.

(A) Acetabularia crenulata (left) and A. mediterranea (right). Each individual is a single cell. The rhizoid contains the nucleus. (B) Effect of exchanging nuclei between two species of Acetabularia. Nuclei were transplanted into enucleated rhizoid fragments. A. crenulata structures are darker, A. mediterranea structures lighter green. (Photographs courtesy of S. Berger.)