A segmentation gene is a

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

involved in the early stages of pattern formation that define repeated units (metameres) in a segmented organism, usually the

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

. They are classified into 3 groups: gap genes, pair-rule genes, and segment polarity genes. The expression of gap genes result in the formation of gaps in the normal pattern of structure in the embryo. Expression of pair-rule genes subdivides the embryo into a series of stripes and sets the boundaries of the parasegments. Segment polarity genes define the anterior and posterior polarities within each embryonic parasegment.

References

Embryology {{Molecular-biology-stub