Ch 16: Development, Stem Cells, and Cancer

Question 1

In Drosophila, cytoplasmic determinants that are localized in the unfertilized egg provide positional information for the placement of anterior-posterior and dorsal-ventral axes even before fertilization.

Answer 1

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Question 2

Edward B. Lewis was a visionary American biologist who, in the 1940s, first showed the value of the genetic approach to studying embryonic development in Drosophila. Lewis studied bizarre mutant flies with developmental defects that led to extra wings or legs in the wrong place (Figure 16.8). He located the mutations on the fly’s genetic map, connecting the abnormalities to specific genes. This research supplied the first evidence that genes direct the developmental processes studied by embryologists. The genes Lewis discovered, called homeotic genes, are regulatory genes that control pattern formation in the late embryo, larva, and adult.

Question 3

Nüsslein-Volhard and Wieschaus eventually identified about 1,200 genes essential for pattern formation during embryonic development. Of these, about 120 were essential for normal segmentation patterns. Over several years, the researchers were able to group these segmentation genes by general function and to clone many of them for further study in the lab. The result was a detailed molecular understanding of the early steps of pattern formation in Drosophila.

Answer 3

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Question 4

When the results of Nüsslein-Volhard and Wieschaus were combined with Lewis’s earlier work, a coherent picture of Drosophila development emerged. In recognition of their discoveries, the three researchers were awarded a Nobel Prize in 1995.