Regulating development in
complex animals
Model organisms are all those in which genetic analysis has been well developed
Drosophila melanogaster:
An insect that produces larva which then undergoes metamorphosis to generate the adult
fly. Shares many parallels with human development:
1. Both humans and drosophila have two axes of symmetry, a dorsal ventral axis(top to
bottom) and an anterior-posterior (front/back)
2. It is SEGMENTED along it anterior-posterior axis like other vertebrates
Its is divided into 3 major segments: head, thorax and abdomen
Polarity/asymmetry:
Axes are set up very early in development
Mutant that are disrupted in their polar patterning can be isolated
These mutants are usually recessive lethals as correct patterning is crucial for their
development
The mutant phenotype Is only seen in the offspring of the double recessive mutant female
parent= maternal effect mutations
The axes of asymmetry are established through the formation of concentration gradients of
transcription factors.
Nuclei in areas of high concentration take up more transcription factors than those in areas
of low concentration. This is a form of POSITIONAL INFORMATION that instructs the nuclei
which genes should be switched on
Morphogenetic gradients establish positional information within the early drosophilia
embryo
Analysis of mutants led to the isolation of genes responsible for positional cues, and analysis
of the gene products that establish the morphogenetic gradients
In order to discover how cells along the gradient interpret their position and differentiate to
create the right structure we must look at segmentation
We can learn positional information by the study of homoeotic mutants- a mutation that
leads to the replacement of a structure with an inappropriate one
Antennapedia mutation- single gene that results in the replacement of the antennae with a
pair of legs, the wild type gene is responsible for initiating the process that results in the
formation of legs in the correct part of the gene
C.elegans
Nematode worm
First animal to have genome sequenced
Acted as test-bed to establish technologies used for Human Genome Project
Excellent model for animal cell differentiation during development
Small (1000 cells), easily cultured, transparent
complex animals
Model organisms are all those in which genetic analysis has been well developed
Drosophila melanogaster:
An insect that produces larva which then undergoes metamorphosis to generate the adult
fly. Shares many parallels with human development:
1. Both humans and drosophila have two axes of symmetry, a dorsal ventral axis(top to
bottom) and an anterior-posterior (front/back)
2. It is SEGMENTED along it anterior-posterior axis like other vertebrates
Its is divided into 3 major segments: head, thorax and abdomen
Polarity/asymmetry:
Axes are set up very early in development
Mutant that are disrupted in their polar patterning can be isolated
These mutants are usually recessive lethals as correct patterning is crucial for their
development
The mutant phenotype Is only seen in the offspring of the double recessive mutant female
parent= maternal effect mutations
The axes of asymmetry are established through the formation of concentration gradients of
transcription factors.
Nuclei in areas of high concentration take up more transcription factors than those in areas
of low concentration. This is a form of POSITIONAL INFORMATION that instructs the nuclei
which genes should be switched on
Morphogenetic gradients establish positional information within the early drosophilia
embryo
Analysis of mutants led to the isolation of genes responsible for positional cues, and analysis
of the gene products that establish the morphogenetic gradients
In order to discover how cells along the gradient interpret their position and differentiate to
create the right structure we must look at segmentation
We can learn positional information by the study of homoeotic mutants- a mutation that
leads to the replacement of a structure with an inappropriate one
Antennapedia mutation- single gene that results in the replacement of the antennae with a
pair of legs, the wild type gene is responsible for initiating the process that results in the
formation of legs in the correct part of the gene
C.elegans
Nematode worm
First animal to have genome sequenced
Acted as test-bed to establish technologies used for Human Genome Project
Excellent model for animal cell differentiation during development
Small (1000 cells), easily cultured, transparent
