Bicoid is a maternal effect gene critical for establishing the anterior-posterior axis in Drosophila embryos. Normally, bicoid mRNA is localized at the anterior pole, creating a gradient of Bicoid protein that specifies head and thoracic structures at the anterior end.

In embryos lacking bicoid, head and thorax structures fail to form. However, experimental injection of bicoid mRNA into different embryo positions alters development as Bicoid protein forms a gradient from the injection site.

When bicoid mRNA is injected into the middle of a bicoid-deficient embryo, Bicoid protein is synthesized locally forming a “new anterior” at the central position. This causes the development of a head and thorax at the middle of the embryo. The regions on both sides of this new “head” develop into thorax structures due to the gradient decline, resulting in thoraxes at both ends.

Thus, the injection creates a duplicated pattern where the middle forms a head and the ends form thoraxes.

Therefore, the correct outcome of bicoid mRNA injection in the middle portion of a bicoid-lacking embryo is:

(2) Head in middle and thoraxes at both ends

Answer: (2) Head in middle and thoraxes at both ends