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
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Gene expression is the activation of a gene that results in a polypeptide or protein being made.
The expression of some genes (regulatory genes) results in the production of a protein that can turn on or switch off other genes, these are called Transcription factors
Mutant with legs growing out of head
The Homeobox is a DNA sequence within the homeotic genes which contains 180 base-pair sequences, coding for a 60 amino acid polypeptide.
The protein binds to an area of the DNA and initiates the transcription of another set of genes. It acts like a switch.
The HOX genes encode important transcription factors. The transcription factors cause proteins to be made that specify cell fate and identify
Homeotic genes involved in spatial pattern control and development contain a conserved 180-bp sequence known as homeobox. This encodes a 60-amino-acid domain that binds to DNA.
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 2 clusters 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.
See page 114
the interior, 3 cell layers formed-
ectoderm, mesoderm and endoderm (e)
Segmented body plan develops (f) driven by
Md, Mx and Lb segments merge to form
3 thoracic segments T1-3
8 abdominal segments A1-8
Larva – free living
Pupa – undergoes metamorphosis
Adult form determined by expression of
Homeotic selector genes
Egg to adult in 10 days
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: Hox c-6 is expanded dramatically toward the head and toward the rear so the snake has no neck and all these vertebrae develop ribs.Hox genes determine the number and types of vertebrae in animals