A segmentation gene

Segmentation gene

A segmentation gene is a gene involved in the early stages of pattern formation that define repeated units in a segmented organism, usually the embryo....

 is a generic term for a gene whose function is to specify tissue pattern

Pattern

A pattern, from the French patron, is a type of theme of recurring events or objects, sometimes referred to as elements of a set of objects.These elements repeat in a predictable manner...

 in each repeated unit of a segmented organism. In the fruit fly Drosophila melanogaster, segment polarity gene

Segment polarity gene

A segmentation gene is a generic term for a gene whose function is to specify tissue pattern in each repeated unit of a segmented organism. In the fruit fly Drosophila melanogaster, segment polarity genes help to define the anterior and posterior polarities within each embryonic parasegment by...

s help to define the anterior and posterior polarities within each embryo

Embryo

An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

nic parasegment by regulating the transmission of signals via the Wnt signaling pathway

Wnt signaling pathway

The Wnt signaling pathway is a network of proteins best known for their roles in embryogenesis and cancer, but also involved in normal physiological processes in adult animals.-Discovery:...

 and Hedgehog signaling pathway

Hedgehog signaling pathway

In a growing embryo, cells develop differently in the head or tail end of the embryo, the left or right, and other positions. They also form segments which develop into different body parts. The hedgehog signaling pathway gives cells information that they need to make the embryo develop properly....

. Segment polarity genes are expressed in the embryo following expression of the gap gene

Gap gene

A gap gene is a type of gene involved in the development of the segmented embryos of some arthropods. Gap genes are defined by the effect of a mutation in that gene, which causes the loss of contiguous body segments, resembling a gap in the normal body plan...

s and pair-rule genes. The most commonly cited examples of these genes are engrailed

Engrailed (gene)

engrailed is a homeodomain transcription factor involved in many aspects of multicellular development. First known for its role in arthropod embryological development, working in consort with the Hox genes, engrailed has been found to be important in other areas of development...

 and gooseberry in Drosophila

Drosophila

Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...

.