Zygotic or Gap genes- any of the genes that transcribed from the DNA (deoxyribonucleic acid) of the fertilized eukaryotic cell known as Zygote.
In drosophila embryogenesis, these zygotic genes can be categorized into segmentation genes. Example gap genes, pair-rule genes, and Segment polarity genes. Zygotic genes are also known as Zygotic-effect genes.
Gap Genes- gap genes are segmentation genes or Zygotic genes (genes involved in the early stages of pattern formation in the embryo) whose expression results in the formation of gaps in the
normal pattern of structure in the embryo. As well as it activates the Pair-rule genes. Gap genes result in the development of broad bands in the embryo.
Both Gap genes and Pair-rule genes are recognized as Zygotic effect genes. Pair rule genes divide the embryo into different pairs of segments. Examples of Pair-rule genes are- even-skipped, hairy, runt, Fushi tarazu, odd skipped, paired, odd paired, etc.
Gap genes were first reported by Christiane Nusslein-Vilhard and Eric Wieschaus in 1980 by using a genetic screen.
The three examples for Gap genes versions are knirps, Kruppel, and a hunchback.
The zygotic genes encode for transcription factors that control the expression of pair-rule genes and homeotic genes.
The gap genes subdivide the embryo along the anterior, posterior axis. The maternal-effect genes which include bicoid and Nanos, are required at the duration of oogenesis and both embryonically transcribed hunchback and maternally-transcribed hunchback got activated by bicoid protein in the anterior and Nanos proteins inhibited in the posterior.
As maternally-transcribed hunchback, embryonically-transcribed hunchback protein is able to exhibit the same effects on Krüppel and knirps.
In Normal flies, the action of Homeotic genes helps in the process of segments like- legs, wings, and antennae. By the time Enter Ed Lewis discovered homeotic mutants where he found structures characteristic of one part of the embryo is found at some other location. The first identification of the genes was in the Fruit fly Drosophila melanogaster.
Genetic Analysis of Drosophila Development:
Much of what we can acknowledge about Drosophila development is on the basis of isolation and characterization of developmental mutants given by three scientists, Ed Lewis, Christiane Nusslein-Volhard, and Eric Wieschaus. All the three scientists were awarded the Nobel prize for their work in 1995. Work was differentiated where Lewis did evolving research on late embryogenesis, while Nusslein-Volhard and Wieschaus concentrated or focused on understanding early embryogenesis.
Picture: October 30, 1980 issue of Nature.
Nusslein-Volhard and Wieschaus came to identify every single gene needed for early pattern formation in the Drosophila embryo. They went in search of recessive embryonic lethal mutations. They classified all of them according to their phenotype.
That is, they looked for and analyzed dead embryos. Images of some of the mutants they identified are shown below.
Read more about gap gene by clicking on the link https://en.wikipedia.org/wiki/Gap_gene
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