BIOEE 1780 Lecture Notes - Lecture 31: Branchial Arch, Repressor, Limb Development
7 May 2018
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When new phenotypes appear in a population:
1. They are sorted by processes like selection, drift, and migration.
2. The sorting results in populations and species changing over time.
Development accounts for phenotypic differences. Phenotypes are modified through modifications of
developmental processes.
• Genes code for proteins.
• Temporal and spatial control of gene expression
• Cell behavior, cell-cell interactions that build size, shape, structure of the embryo
Developmental processes connect genotype with phenotype.
Do some kinds of DNA mutations produce more significant and coordinate change than others?
• Yes, small changes in genotype (as played out through development) can profoundly change the
phenotype.
Morphological Evolution Occurs Through…
1. Changes in timing and location of gene expression during development (known as Regulatory
Evolution)
a. Caused body plans to change
b. Example
i. Imaginal discs: nascent adult organs in insect larvae; clusters of cells in larvae that grow
rapidly to form large features in the adults (i.e. mouth parts, antennae, leg)
ii. Ultrabiothorax (Ubx) is expressed in haltere (segment on thorax of drosophila), but not
expressed in the wing segment.
iii. When Ubx is knocked out, that segment becomes identical to the wing segment (2 sets of
wings).
c. Primitive insect wings look similar. More "modern" insect wings are diverse.
i. Step 1: differentiate
ii. Step 2: diversify
2. Duplication and subsequent functional changes of genes that control development (known as Gene
Duplication)
Hox Genes: specify body segments and what appendages develop on each segment
• The same genes are used to specify segments in all animals.
o Genes are in the same spatial order (anterior to posterior).
o Hox genes are conserved in all animals.
• The more complex the animal, the greater the number of Hox genes.
• Formally, sponges don't have true Hox genes. They have ParaHox genes (close relatives of
Hox genes).
• There is currently a debate whether sponges lost Hox genes.
• Duplication of a hox gene can cause one of the redundant genes to take on different functions.
o Gene duplications to Hox genes are associated with increasing body plan complexity.
• Antennapedia Gene: controls the formation of legs
• Encode Transcription Factors (proteins that regulate the expression of other genes)
Hox genes are genetic toolkit genes. These are ancient, evolutionarily conserved developmental genes
that exert a high level control over organismal structure.
Document Summary
When new phenotypes appear in a population: they are sorted by processes like selection, drift, and migration, the sorting results in populations and species changing over time. Phenotypes are modified through modifications of developmental processes: genes code for proteins, cell behavior, cell-cell interactions that build size, shape, structure of the embryo. Yes, small changes in genotype (as played out through development) can profoundly change the phenotype. Morphological evolution occurs through : changes in timing and location of gene expression during development (known as regulatory. Evolution: caused body plans to change, example. Imaginal discs: nascent adult organs in insect larvae; clusters of cells in larvae that grow rapidly to form large features in the adults (i. e. mouth parts, antennae, leg) Step 2: diversify: duplication and subsequent functional changes of genes that control development (known as gene. Hox genes: specify body segments and what appendages develop on each segment.
