Homeobox Genes. Body organisation. Cell Differentiation. Cell differentiation is the development of non-specialised cells into cells with specialised functions. Examples: muscle cells, liver cell, red blood cells
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Gene expression is the activation of a gene that results in a polypeptide or protein.
The expression of some genes results in the production of a protein that can turn on or switch off other genes. Transcription factors
Mutant with legs growing out of head
The Homeobox is a coding sequence within homeotic genes which contains 180 base-pair sequences, codes for 60 amino acid polypeptide
Encodes homeodomainfor DNA binding
The HOX genes encode important transcription factors. These specify cell fate and identify
In Humans as in most vertebrates there are 4 homeobox gene clusters (39 HOX genes), located on chromosomes 7p14, 17q21,12q13 and 7q31.
Drosophila has eight Hox genes arranged in a single cluster on a single chromosome.
A.Drosophila's eight Hoxgenes in a single cluster and 39 HOX genes in humans.B. Expression patterns of Hoxand HOX genes along the anterior-posterior axis in invertebrates and vertebrates.
Fertilised egg establishes the pattern for the adult body plan
Elongated cell with positional information
After fertilization, zygote develops into blastoderm
Series of nuclear divisions without cytoplasmic division (produces many free nuclei) synctialblastoderm
Individual cells are created after nuclei line up along cell membrane (cellular blastoderm)
See page 114
Organize body along major axes
Organize into smaller regions (organs, legs)
Cells organize to produce body parts
Cells themselves change morphologies and become differentiated
Snake: Hoxc-6 is expanded dramatically toward the head and toward the rear so all these vertebrae develop ribs.Hox genes determine the number and types of vertebrae in animals