A pair-rule gene is a type of

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

involved in the

development Development or developing may refer to: Arts *Development (music), the process by which thematic material is reshaped * Photographic development *Filmmaking, development phase, including finance and budgeting * Development hell, when a proje ...

of the segmented

embryos An embryo ( ) is the initial stage of development for 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 ...

insects Insects (from Latin ') are hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed ...

. Pair-rule genes are expressed as a result of differing concentrations of gap gene proteins, which encode

transcription factors In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The fun ...

controlling pair-rule gene expression. Pair-rule genes are defined by the effect of a

mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, ...

in that gene, which causes the loss of the normal developmental pattern in alternating segments. Pair-rule genes were first described by

Christiane Nüsslein-Volhard Christiane (Janni) Nüsslein-Volhard (; born 20 October 1942) is a German developmental biologist and a 1995 Nobel Prize in Physiology or Medicine laureate. She is the only woman from Germany to have received a Nobel Prize in the sciences. N� ...

and

Eric Wieschaus Eric Francis Wieschaus (born June 8, 1947 in South Bend, Indiana) is an American Evolutionary developmental biology, evolutionary developmental biologist and 1995 Nobel Prize-winner. Early life Born in South Bend, Indiana, he attended John Carro ...

in 1980. They used a genetic screen to identify genes required for embryonic development in the fruit fly ''

Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (an insect of the Order (biology), order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly", "pomace fly" ...

''. In normal unmutated ''Drosophila,'' each segment produces bristles called denticles in a band arranged on the side of the segment closer to the head (the

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

). They found five genes – ''even-skipped, hairy, odd-skipped, paired'' and ''runt'' – where mutations caused the deletion of a particular region of every alternate segment. For example, in ''even-skipped,'' the denticle bands of alternate segments are missing, which results in an embryo having half the number of denticle bands. Later work identified more pair-rule genes in the ''Drosophila'' early embryo – ''fushi tarazu'', ''odd-paired'' and ''sloppy paired''. Once the pair-rule genes had been identified at the molecular level it was found that each gene is expressed in alternate ''parasegments'' – regions in the embryo that are closely related to segments, but are slightly out of register. Each parasegment includes the posterior part of one (future) segment, and an anterior part of the next (more posterior) segment. The bands of expression of the pair-rule genes correspond to the regions missing in the mutant. The expression of the pair-rule genes in bands is dependent both upon direct regulation by the gap genes and on regulatory interactions between the pair-rule genes themselves.

References

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External links

* The Interactive Fly: http://www.sdbonline.org/fly/aignfam/gapnprl.htm Developmental genes and proteins

See also

References

External links