Transvection

Zygotic Gene Activity in Development

The differentiation of cell types and the formation of organs depend on genes

being activated in particular spatial and temporal patterns.

Zygotic Gene Expression

The earliest events in animal development are controlled by maternally synthesized factors.

At some point after fertilization, zygotic gene expression, or expression of genes from the embryo’s genome, begins.

The initial wave of zygotic gene expression is a response to maternally synthesized factors. As development proceeds, activation of zygotic genes leads to complex cascades of gene expression.

Body Segmentation in Drosophila

Cuticle patterns-Denticle belts

Homeotic Genes

Homeotic mutations transform one segment into another; this is called homeosis.

Mutation in bithorax (bx) affect two thoracic segments.

Mutations in Antennapedia transform the antennae into legs.

The Homeotic Genes of Drosophila

The Drosophila homeotic genes form two large clusters on one of the autosomes.

All of the homeotic genes encode helix-turn-helix transcription factors with a conserved homeodomain region involved in DNA binding. These genes control a regulatory cascade of target genes that control segment identity.

The expression pattern of these genes along the anterior-posterior axis corresponds to the order of the genes along the chromosome.

The Bithorax and Antennapedia Complexes of Drosophila

Organ Formation

Organ formation requires the organization of many different types of cells.

Organ formation is under genetic control.

The eyeless Gene

Mutant flies lack eyes.

The wild-type eyeless gene encodes a homeodomain transcription factor that activates a pathway involving thousands of genes.

Expression of eyeless in Other Tissues Causes Formation of Extra Eyes

Mammalian Homologues of eyeless

The mouse homologue of eyeless, Pax6, produces extra eyes when it is inserted into Drosophila.

In mice, mutations in the eyeless homologue reduce the size of the eyes.

Mutations in the human homologue cause aniridia.

Two Hybrid

Genetic Analysis of Development in Vertebrates

Geneticists can study development in vertebrates by applying knowledge gained from the study of model

invertebrates, by analyzing mutations and phenocopies of mutant genes in model vertebrates such as mice

and zebrafish, and by examining the differentiation of stem cells.

The Mammalian Hox Genes

Evolution of the Hox Genes

The four mammalian Hox gene clusters were created by quadruplication of a primordial cluster early in vertebrate evolution.

The organization of the HOM/Hox genes has been preserved during evolution.

Within each cluster, the physical order of the Hox genes corresponds to their anterior-posterior expression pattern.

T2A1

61 aminoAcid conservedDNA Binding Sequence