Final answer:
Hox genes dictate the body plan of an organism, and swapping a Hox 13 gene with a Hox 1 in a mouse could cause major developmental issues, potentially resulting in misplaced or malformed body parts.
Step-by-step explanation:
Hox genes are crucial in the development of an organism, acting as master control genes for body plan layout. If in a mouse embryo, a Hox 13 gene is replaced by a Hox 1 gene, it could lead to a significant alteration in the body segment that the gene influences. Considering Hox genes are highly conserved and responsible for the proper formation of body structures, such a replacement could result in morphological anomalies where body parts may develop incorrectly, akin to how a leg grew out of the head of a mutated fruit fly instead of an antenna.
The answer to the visual connection question on a test about what phenotype is likely the result of a Hox gene mutation should be (a) abnormal body length or height or (d) two fewer appendages than normal. Mutations in these genes can lead to large scale defects in the body plan such as extra appendages, misplacement of body parts, or complete changes in the segment identity along the anterior-posterior axis of the organism.