Concept 37 Master genes control basic body plans.
Cross pure-bred pea plants to identify dominant flower color.
HI! Early Drosophila development depends on the correct distribution of maternal proteins in anterior/posterior (A/P) and the dorsal/ventral (D/V) axis. The A/P axis is set up by a protein called BICOID that is expressed in a anterior-to-posterior gradient. What will happen to an embryo that doesn't have any BICOID protein? Nothing, as long as the dorsal/ventral gradient is present, the embryo will develop normally. No, BICOID is needed for anterior structures. The embryo will develop without any anterior structures and will eventually die. That is correct. The embryo will develop without any dorsal or ventral structures and will eventually die. No, the dorsal/ventral gradient is not dependent on BICOID expression. The dorsal/ventral gradient takes over and sets up another dorsal/ventral axis. No, a new dorsal/ventral gradient will not be set up. BICOID sets up the A/P axis, and is necessary for the formation of anterior structures. Without the bicoid protein, as in the null mutant, anterior structures do not form properly and the embryo eventually dies. These photos show a wild-type Drosophila embryo that developed with normal BICOID levels and a mutant that did not have any BICOID. Without "anterior" instructions, the embryo defaults and makes posterior structures at both ends. In some mutations, overexpression of protein is possible. What do you think happens when BICOID is overexpressed? Nothing, as long as there is an A/P axis, the embryo will develop normally. No, when overexpressed the BICOID gradient shifts. Anterior structures won't form now because there is too much BICOID. No, anterior structures can still form. The embryo will develop more anterior structures and less posterior ones, and will eventually die. That is correct. None of the above. No, there is a correct answer. With more BICOID, more anterior structures form further along the A/P axis. The effective concentration of BICOID has increased at the anterior points. This image shows the embryonic expression pattern of a Drosophila protein called HAIRY (seen in yellow). Based on what you know, what kind of gene is hairy? A gene that sets up the dorsal/ventral axis. No, hairy is not expressed in a gradient. A pair rule gene. That is correct. A gap gene. No, hairy is not expressed in sections. hairy is a pair rule gene. It is expressed in the Drosophila embryo; it also defines segments of it. Mutants have fused segments and some have extra bristles, hence the name "hairy." This is a leg from another Drosophila mutant. In this mutant, the eyeless gene is expressed in the leg, and the result is an eye growing out of place, ectopically. The new eye isn't ennervated so the Drosophila cannot "see" out of it. However, the functional parts of a Drosophila eye are present. In this case, eyeless is an example of what kind of gene? Embryonic lethal. No, the embryo lived to grow adult structures. Segment polarity. No, segment polarity genes affect the A/P orientation of individual segments. Homeotic. That is correct. A/P axis determinant, specific for head structures. No, A/P axis determinants cannot specify body parts. eyeless is a homeotic gene because it has the ability to specify a body part. In this example, eyeless transformed part of the leg into an eye.