Question

How do segment polarity genes differ in their mode of action from the gap and pair-rule genes? Explain why and give examples.

Answer 1

Ans :

The gap, pair-rule and segment polarity genes are together called the segmentation genes because these genes are involved in segment patterning of body parts during embryonic development. The gap genes subdivide the embryo while the pair-rule genes divides the embryo into pairs of segments. The segment polarity genes establish the anterior/posterior axis of each segment. The gap genes encode transcription factors that regulate the expression of the pair-rule genes while pair-rule genes encode transcription factors that regulate the expression of the segment polarity genes.

Mode of Action of segment polarity genes

One example for this is Drosophila, which is a normal fly. For their body parts such as structures like legs, wings, and antennae to develop on particular segment it requires an action processed by a particular genes known as homeotic genes. These are responsible for encoding transcription factors that control the expression of genes responsible for structures such as legs,wings, and antennae. The homeotic genes include a 180 nucleotide sequence called homeobox or HOX genes and is translated into a 60 amino acid domain, called homeodomain. The homeodomain is involved in DNA binding during the development of embryo(embryogenesis) in Drosophila. These HOX genes are found in clusters and they are expressed along anterior/posterior axis. Another examples are Frog and Mouse.