Module 10 Study Guide

collinearity

(within the context of evo-devo): as seen in the HOX example of drosophila, colinearity describes the parallel body plan-chromosome arrangement observed in animals

five properties of a kernel

-These are network subcircuits that consist of regulatory genes (i.e. genes encoding transcription factors) -They execute the developmental patterning functions required to specify the spatial domain of an embryo in which a given body part will form -Kernels are dedicated to given developmental functions and are not used elsewhere in development of the organism (though individuals genes of the kernel are likely used in many different contexts) -They have a particular form of structure in that the products of multiple regulatory genes of the kernel are required for function of each of the participating cis-regulatory modules of the kernel -Interference with expression of any one kernel gene will destroy kernel function altogether and is likely to produce the catastrophic phenotype of lack of the body part. The result is an extraordinary conservation of kernel architecture

homeotic genes

AKA transcription factors; encode proteins that regulate expression of genes that determine how these cells develop; Determines which downstream gene is expressed, like lacZ expression

Haeckel

Biogenetic law

Good change in a gene regulatory network

Change in sequence of regulatory region can result in weak pleiotropy, which are not deleterious and possible lead to variations. Regulation is the key to diversity

Bad change in a gene regulatory network

Change in the coding sequence of major regulatory genes can exhibit strong "pleiotropy" or effects on other genes they regulate

importance of HOX genes

HOX genes are very conserved and there's a lot of homologous functions across large phenotypic distances. Strong conservation suggests that there are particular functions that are critical to the development of the organisms that they evolve very slowly

gene duplication events correlate with increasing cellular diversity and organismal complexity

HOX genes go back to cnidarians. Cnidarians are simple, one of the most ancient multicellular animals. But HOX genes are the fewest in this species, so that supports the idea that duplications of HOX genes as well of replications of entire sections of JOX genes correlates with increasing levels of cellular diversity Vertebrates have more copies of HOX genes than vertebrates. Why? Because as you've had these duplications, you end up with opportunities for new functions to arise. These duplications give rise to lots of paralogs that exist (paralogs are when you have duplications within a genome as present within a species) which is distinct from orthologs

Parts of a gene regulatory network

Kernel, differentiation gene batteries

significance of Jacob and Monod

LacZ is responsive to the environment around it. And why is this relevant when we're thinking about development, where you don't have any change in any of these genes, but simply you have a modification of how these genes regulate it, can lead to a very dramatic phenotypic outcome: either the production of the genes involved in breaking down lactose, or nothing is made at all.

Gene regulatory networks

a collection of molecular regulators that interact with each other and with other substances in the cell to govern the gene expression levels of mRNA and proteins.

lac operon

a gene system whose operator gene and three structural genes control lactose metabolism in E. coli

Van Baer

also worked on biogenetic law. proposed that closely related species had similar developmental traits,and that these traits, because they are important early in life, they are highly resistant to change. And so essentially what that said is that closely related organisms had resembled, early on in development, one another. As in some ways, evidenced across these different vertebrates. And so it is throughout development that they would then distinguish themselves. he was wrong too.

von Baer's law

biogenetic law

PAX

critical for eye development. Even though eyes across species are different, we find orthologs of these PAX genes (very conserved!)

Haeckel vs Von Baer

development stages recapitulate adult evolutionary stages no recapitulation: embryos development increasingly diverse

biogenetic law

developmental progress reflects the evolutionary history of the organisms, and that evolutionary processes could add novelty at the end of development. So early in development, these reflect ancient, fundamental processes, or the ancient forms of the organisms, and then near the end of the development is where you had the emergence of variation.

Jacob and Monod

discovery of how lactose is broken down into glucose and galactose

why is biogenetic law problematic?

every stage of development is subject to the forces of evolution. there are various genes that are involved in regulating how an organism develops and goes through all of its stages of maturation, all of those genes are subject to various evolutionary forces, and therefore, development isn't just simply playing out phylogenetic history, but that every stage of development can be impacted by these evolutionary forces. At the time researchers lacked awareness of the genes and how different evolutionary forces are acting upon genes.

Kernel

evolutionarily inflexible subcircuits that perform essential upstream functions in building given body parts

Regulatory enhancers

gene switches (DNA sequences) that are bound by transcriptional regulators

Orthologs

genes in different species that evolved from a common ancestral gene by speciation, and, in general, they retain the same function during the course of evolution.

Differentiation gene batteries

groups of protein-coding genes under common regulatory control, the products of which execute cell type-specific function. Such functions contrast with kernels, the significance of which is entirely regulatory. Only at the end of the formation process are deployed the differentiation gene batteries that encode the detailed functional properties of the body part.

HOX

homeotic genes whose products direct cellular development by coordinating the expression of genes within its "regulome". AKA they control body plan of embryo during development

homeotic mutant

in this homeotic mutant, you actually have a duplication of some sort that has led to their being double, or an extra pair of wings in this particular individual. And so small changes in Hox can have huge impacts in development.

scala naturae

life-forms could be arranged on a scale of increasing complexity, with humans at the top. Plato and Aristotle.

MADS:

master regulator that controls flower development

what do differentiation gene batteries build?

muscle cells, make skeletal biominerals, skin, synaptic transmission systems, etc.

Evolutionary developmental biology "Evo-devo"

seeks to understand how the genetic machinery underlying organismal maturation change over time and how maturation programs between species can suggest ancestral relationships between different species and how those species have emerged.

changes in transcriptional regulation can have small and large phenotypic consequences

think of Jacob and Monod & HOX genes

T/F: genes involved early development are highly conserved across highly diverged animals

true