The three homeodomain proteins Abd-B, Abd-A, andUbx are encoded by genes within the Bithorax complexof Drosophila. In wild-type embryos, the Abd-B gene isexpressed in the posterior abdominal segments, Abd-Ain the middle abdominal segments, and Ubx in the anterior abdominal and posterior thoracic segments. Whenthe Abd-B gene is deleted, Abd-A is expressed in both themiddle and the posterior abdominal segments. WhenAbd-A is deleted, Ubx is expressed in the posterior thoraxand in the anterior and middle abdominal segments.When Ubx is deleted, the patterns of Abd-A and Abd-Bexpression are unchanged from wild type. When bothAbd-A and Abd-B are deleted, Ubx is expressed in all segments from the posterior thorax to the posterior end ofthe embryo. Explain these observations, taking into consideration the fact that the gap genes control the initialexpression patterns of the homeotic genes
The three homeodomain proteins Abd-B, Abd-A, and
Ubx are encoded by genes within the Bithorax complex
of Drosophila. In wild-type embryos, the Abd-B gene is
expressed in the posterior abdominal segments, Abd-A
in the middle abdominal segments, and Ubx in the anterior abdominal and posterior thoracic segments. When
the Abd-B gene is deleted, Abd-A is expressed in both the
middle and the posterior abdominal segments. When
Abd-A is deleted, Ubx is expressed in the posterior thorax
and in the anterior and middle abdominal segments.
When Ubx is deleted, the patterns of Abd-A and Abd-B
expression are unchanged from wild type. When both
Abd-A and Abd-B are deleted, Ubx is expressed in all segments from the posterior thorax to the posterior end of
the embryo. Explain these observations, taking into consideration the fact that the gap genes control the initial
expression patterns of the homeotic genes
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