Evolution of Morphology and Developmental Genetics (Evo-Devo)

Vocabulary practice flashcards covering evolutionary developmental biology (Evo-Devo), genetic toolkit proteins, regulatory versus coding sequence divergence, and case studies including sticklebacks, Drosophila, and mammalian limb elongation.

Evo-Devo

The study of evolutionary developmental biology, based on the principle that development gives rise to form, meaning that the evolution of form is brought about through the evolution of development.

Developmental Genes

Genes that program development and control the rate, timing, and spatial pattern of changes in an organism's form as it develops into adulthood.

Genetic Toolkit

The conserved collection of developmental genes responsible for building bodies and body parts that is shared across virtually all animals.

Slow worm

A limbless lizard that serves as an example of morphological divergence within squamate reptiles.

Ectopic Eye Induction (Halder et al., 1995)

An experimental demonstration showing that targeted expression of the Drosophila eyeless gene produces extra eyes, proving that mammals and insects share a functionally equivalent master control gene despite separating over $500\text{ million years}$ ago.

Metamorphosis

A developmental process seen in organisms such as sea urchins, frogs, and butterflies where dramatically different body morphologies and ecological stages are produced from the identical genome and toolkit proteins.

Imaginal Disks

Clusters of embryonic cells present in the third instar larva of Drosophila melanogaster that develop into adult external structures during pupation and eclosion.

Genetic Theory of Morphological Evolution

A theory proposed by Sean Carroll stating that form evolves largely by altering the expression of functionally conserved proteins, predominantly through mutations in the promoter sequences of regulatory and target genes.

Transcription Factor

A regulatory protein that binds to specific DNA sequences (cis-regulatory elements) to control the transcription of genetic information from DNA to RNA.

Cis-regulatory Element

A non-coding DNA sequence within promoters or enhancers that transcription factors bind to in order to increase or modulate the transcription of a gene.

Prx1 Gene

A developmental gene involved in limb formation whose cis-regulatory promoter determines limb length in mammals.

BatE/BatE Transgenic Mice

Transgenic mice generated by replacing the mouse Prx1 promoter with the fruit bat Prx1 promoter (which shares $94\%$ sequence similarity), causing the mice to develop significantly longer forelimbs.

Threespine Stickleback (Gasterosteus aculeatus)

A fish species whose lake populations exhibit loss of ventral pelvic spines due to changes in developmental gene regulation compared to marine relatives.

Pitx1 Expression Divergence

The mechanism of spine reduction where marine stickleback embryos express Pitx1 in both the mouth and ventral pelvic region, whereas lake sticklebacks express it only in the mouth due to an altered pelvic regulatory region, despite having identical $283\text{-amino acid}$ Pitx1 coding sequences.

Ultrabithorax (Ubx)

A Hox gene (Hox gene 7) whose expression suppresses leg formation in insect genital/abdominal segments, but does not suppress legs in crustacean ancestors.

QA Repression Domain

A domain that evolved in insect Ubx alongside the loss of serine/threonine phosphorylation sites, enabling Ubx to repress Distal-less and turn off abdominal leg development.

Distal-less Repression

The targeted transcriptional silencing of the Distal-less gene by insect Ubx, mediating the evolutionary transition from multi-legged ancestors to six-legged insects.

Lophotrochozoa vs. Ecdysozoa

The two major molecularly defined protostome clades: Lophotrochozoa is characterized by trochophore larvae or lophophore feeding crowns, whereas Ecdysozoa is characterized by cuticular molting (ecdysis).

Morphological vs. Molecular Protostome Phylogeny

Morphological phylogenies group Annelida and Arthropoda together based on shared body segmentation, whereas molecular phylogenies (based on rRNA) divide protostomes into Lophotrochozoa and Ecdysozoa (molting animals).

Purpose of Studying Evo-Devo

Development is the process that gives rise to form; therefore, the evolution of anatomical form is directly brought about through the evolution of developmental mechanisms.

Hox Genes

Homeobox transcription factors that specify regional identity along the anterior-posterior (A-P) body axis in animal embryos, characterized by colinearity where the chromosomal gene order directly mirrors the spatial and temporal order of expression.