Question

Compare and contrast the terms homeosis, homeodomain, and Hox genes. (ii) In a few sentences, describe how Hox genes work. (iii) How did Hox genes originate? (iv) What do homeotic mutations tell us about the genotype-phenotype map? (v) Hox genes are highly conserved; explain in 1-3 sentences why the same set of genes may function similarly in widely different animals.

Answer 1

(1)Homeosis:The formation of a normal structure or organ in place of another at an abnormal site, as caused by the expression of a mutated hox gene.

Homeodomain: It is a particular DNA sequence that provides instructions for making a string of 60 protein building blocks (amino acids) in homeobox. Mostly they act as transcription factors, which means they bind to and control the activity of other genes. Homeobox: These are regions of similarity in protein sequence, which encode DNA binding activity.

HOX genes: They regulate to divide the anterior-poster axis of most metazoans. They are defined functionally by their homeoboxes, and by their arrangement in gene clusters.

(2)Hox genes work as : Hox genes are found in many animals, including fruit flies, mice, and humans. In human Hox gene mutations can cause genetic disorders.

Homeotic genes encode transcription factor proteins containing a region called the homeodomain and are called Hox genes.

Hox genes are turned on by a cascade of regulatory genes, these are the proteins encoded by early genes that regulate the expression of later genes.

(3) Hox gene has a main function in body development during animal progress . By recent data about hox gene from Cnidaria, a basal animal phylum and by characterization of Hox-like genes from Hydra, sea anemones and jellyfish has revealed that a Hox gene cluster is extremely ancient, having originated even before the evolutionary divergence of these basal animals.

(4) Genotype is an organism's full hereditary information. Phenotype is an organism's actual observed properties, such as morphology, development, or behavior. This helps in study of evolution and inheritance.

So, with homeotic mutation, the phenotype will be affected. This will surely lead to change in pattern of genotypic phenotypic mapping.

(5) Hox gene conservation and why same set of genes may function similarly in widely different animals.

• Hox genes are conserved during metazoan evolution and they are present in organisms ranging from primitive chordates to humans.
• Same set of hox gene function differently in different organisms because hox genes are grouped in chromosomal clusters with the number of clusters varying according to organismal complexity.
• The relative position of Hox genes inside the clusters reflects their expression pattern along the anterior–posterior axis of the given organisms.