Final answer:
Mutations in gap genes are responsible for mutant embryos missing large, contiguous groups of segments. Pair-rule genes, segment polarity genes, and homeotic genes (including Hox genes) also play crucial roles in segment development, but their mutations typically lead to different types of phenotypic abnormalities.
Step-by-step explanation:
Defects in gap genes result in mutant embryos that are missing large, contiguous groups of segments. Gap genes are essential in early embryonic development in Drosophila (fruit flies) and define broad areas of the embryo. Mutations in these genes lead to the absence of several consecutive segments. Comparatively, pair-rule genes affect alternating segments, segment polarity genes disturb the anterior-posterior organization within individual segments, and homeotic genes (which include Hox genes) control the specific structures that develop within each segment, so mutations can lead to body parts forming in the wrong location, like legs where antennae should be.
Regarding the type of mutations referenced in related questions: A mutation in Hox genes would most likely result in phenotypes such as abnormal body length or height, or in a specific case, appendages forming in unexpected locations, like the mentioned extra wings or legs growing in place of antennae in Drosophila.