Genomics and developmental biology Flashcards
Why do we say that the genome’s implementation in cells is dynamic
Genomes are statistic data sets. Genomes contain developmental programmes governing expression patterns of genes at different life stages, in differentiated tissues and reactions and responses to environmental stimuli.
Provide examples to illustrate the fact that different species show very different body plans despite high similarities in their genes and proteins, different taxa can also show high similarities in their developmental toolkits(sets of genes active in guiding development)
> Homeotic genes are responsible for the organization of anterior-posterior(head-to-tail) patterning in the body plans of flies, humans, and even nematodes.
The human paired box gene PAX6 is required for proper eye development, but if it is expressed in Drosophila it can transform embryonic wing tissue to an ectopic( out-of-place) eye.
The implication is that despite the very great differences in the gross anatomy of the eyes in vertebrates, insects, and octopuses, the visual systems arose from a common ancestor. The evidence to support this statement is that both the molecular structures of the initial light receptors(the rhodopsins and the architecture of neural pathways) confirm this conclusion.
How do we track the similarities and differences in the developmental process of organisms during evolution
By looking at the full genome sequences
How do we identify homologues of genes across different phyla
By looking at the developmental toolkits(sets of genes that are active in guiding development) across different phyla.
Explain how full-genome sequences allow the tracking of similarities and differences in the developmental process during evolution
> it is possible to identify homologues of genes by looking at the developmental toolkits across different phyla
Make use of and illuminate phylogenetic relationships- an extrapolation(to the molecular level) of the classical application of embryology to taxology.
Provide an example of how the correct taxanomic assignment of species with unusual features can reveal phylogenetic and developmental relationships
The phylum Cnidaria contains almost 10000 species of aquatic animals, eg. sea anemones and jellyfish. The worm Buddenbrockia plumatalle was, until recently an enigma. Its body plan did not resemble the familiar radially symmetrical Cnidaria, it might be easily thought to be related to nematodes. However, scientists have shown on the basis of sequence alignments of 129 proteins that B.plumatellae is a Cnidarian. This extends the body plan observed for cnidaria, so requiring investigation of unsuspected aspects of the developmental pathways in this species.
Provide a classical example of how genomes illuminate developmental biology both within and among species
HOX genes- organisms with bilateral symmetry, including insects and vertebrates, contain HOX genes, which encode a family of DNA-binding proteins. The expression of these genes varies along the anterior-posterior body axis and controls the setting out of the body plan. HOX genes have overlapping domains of expression within the body. Different regions of the embryo develop into anatomically distinct regions of the adult based on the subset of HOX genes expressed. There is a fascinating mapping between the order of the genes on the chromosome, the relative times of during development of the onset of their activity, and the order of their action along the body. HOX genes reveal the duplications that have occurred during vertebrate evolution- insects and amphioxus have a single HOX cluster, humans have 4 and zebrafish have 7( 1,2,4,8- with the loss of 1). The HOX genes illustrate the conservation of the developmental toolkit in species with different body plans.
Discuss methylation patterns
The distribution of DNA methylases illustrates the diversification of developmental toolkits, even in organisms with similar body plans. DNA methylation patterns are important signals for transcription control in vertebrae development and tissue differentiation. In contrast many invertebrates show little or no DNA methylation. Examples, C.elegans and Drosophila melanogaster, the first two invertebrate genomes sequenced. These observations would assume that DNA methylation arose in the vertebrate lineage. However, C.elegans lacks the genes for DNA methylases and Drosophila has some, the genome sequences of related nematodes and insects show that the genes were present in invertebrates and some or all have been lost in specific lineages that lead to C.elegans and drosophila. For instance honeybees contain DNA methylase genes and its DNA is methylated. However it appears that invertebrates and vertebrates differ in the pattern and function of DNA methylation.
