A pair-rule gene is a type of
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 b ...
involved in the
development
Development or developing may refer to:
Arts
*Development hell, when a project is stuck in development
*Filmmaking, development phase, including finance and budgeting
*Development (music), the process thematic material is reshaped
* Photograph ...
of the
segmented embryos
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 ...
of
insects
Insects (from Latin ') are pancrustacean 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 j ...
. Pair-rule genes are expressed as a result of differing concentrations of
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 norm ...
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 replication, DNA or viral repl ...
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.
NÃ ...
and
Eric Wieschaus
Eric Francis Wieschaus (born June 8, 1947 in South Bend, Indiana) is an American evolutionary developmental biologist and 1995 Nobel Prize-winner.
Early life
Born in South Bend, Indiana, he attended John Carroll Catholic High School in Birming ...
in 1980. They used a
genetic screen
A genetic screen or mutagenesis screen is an experimental technique used to identify and select individuals who possess a phenotype of interest in a mutagenized population. Hence a genetic screen is a type of phenotypic screen. Genetic screens c ...
to identify genes required for embryonic development in the fruit fly ''
Drosophila melanogaster
''Drosophila melanogaster'' is a species of fly (the taxonomic 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" or "pomace fly". Starting with ...
''. 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). 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 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 norm ...
s and on regulatory interactions between the pair-rule genes themselves.
See also
*
''Drosophila'' embryogenesis
*
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 norm ...
References
{{reflist
External links
* The Interactive Fly: http://www.sdbonline.org/fly/aignfam/gapnprl.htm
Developmental genes and proteins