Developmental Genetics Lecture 7

Developmental Genetics Lecture 7

• Lecture Objectives: Students will be able to:
  • Discuss differential gene action.
  • Describe gene action mechanisms in prokaryotes and eukaryotes.
  • Explain gene control in development.

What is Developmental Genetics?

• Studies the relationship between gene regulation and cell differentiation during development.
• A fertilized egg develops into an adult organism through regulated growth.
• Development is the result of the genome interacting with the cytoplasm and environment.
• Development involves multiple gene actions.
• The phenotype is the expression of the genotype.
• Development involves a programmed sequence of phenotypic events that are typically irreversible.
• Development requires the formation of different cell types.
• All cells have identical genotypes.
• Regulatory events lead to diverse cellular phenotypes.

Differential Gene Action: The Basis of Cell Differentiation

• After fertilization, the zygote undergoes embryogenesis.
• Active cell division occurs.
• Different cell types are formed.
• Determination: A cell commits to a specific developmental path irreversibly.
• Differentiation: The cell expresses its specialized role.

Initial Cytoplasmic Environment

• The initial cytoplasmic environment in the embryo is provided by the maternal genome.
• Cytoplasmic determinants initiate the activation of genes.

Embryonic Development

• Embryonic development involves a sequence of changing cell populations.
• This progression shows a complex pattern of development.

Considerations

• Properties of differentiated cells reflect the activity of specific genes.
• Cells with the same genotype have varying activity.
• A cell typically manifests only a fraction of its genes.
• Genes and chromosomes are uniformly distributed.
• Chemical environments inside the cell differ.
• Environmental factors can affect the expression of genes.
• Differential gene regulation leads to diverse functions.

Cell Diversity

• Different cell types (sex, muscle, fat, immune, epithelial, nerve, blood, bone) originate from a stem cell.

Enzyme Structure and Cell Differences

• Differences in differentiated cells could be largely due to differences in enzyme composition.
• Enzyme structure is determined by the DNA.
• Protein appearance correlates with active genes.
• Qualitative differences in protein content between cells indicate differences in the schedules of gene activation.

Selective Gene Expression in the Phenotype

• The final phenotype results from selective gene expression at different stages of cell metabolism.
• Pre-transcriptional control is a step in gene expression.
• Transcriptional control is another step in gene expression.
• Translational control also contributes to gene expression.
• Post-translational modification fine-tunes gene expression.

Pre-Transcriptional Control

• Gene amplification, observed in oocytes of some species and embryonic cells.
• Chromatin condensation/decondensation regulates gene expression.

Transcriptional Control

• Differential initiation is a key aspect of transcriptional control.
• Differential splicing results in different mRNA products from a single gene.

mRNA Degradation

• Selective pre-mRNA degradation is another factor in controlling gene expression.

Translational Control

• Selective translation is involved.
• mRNA stability influences gene expression.

Post-Translational Modification

• Modifications like deletion of peptide parts, changes in the state of oxidation/reduction, attachment of small molecules, and polymerization/combination with phosphate groups are all part of this process.