The answer is hox gene.
Hox genes are responsible for an embryo's body plan. They determine different body structures - legs, vertebrae, antennae, wings, depending on groups. Mutation in hox genes is serious mutation since it affects the early stages of embryo and consequently, normal development. If a mutation occurs in the hox gene for legs growth, the legs will not develop.
A mutation is a rare, accidental or induced modification of genetic information (DNA or RNA sequence) in the genome.
The consequences of a mutation vary according to the part of the genome affected. A mutation is said to be hereditary if the mutated genetic sequence is passed on to the next generation.
In multicellular animals, germline mutations can be transmitted to offspring, whereas somatic mutations do.
Somatic mutations do not affect cells intended for reproduction, so they are never hereditary:
* Post-zygotic mutations are the mutations that appear in the egg after fertilization. They are rarer and are expressed as mosaic in the individual concerned (the mutation will be present only in the daughter cells originating from the mutated embryonic cell).
* Mutations can appear throughout life on the DNA of any cell; they are then transmitted to the line of the daughter cells. These can, in some cases, become tumor cells and then form cancer.
D! The Cell membrane in found in all cells, and it is a single (mono) layer.
