BIOE 20C Lecture Notes - Lecture 6: Evolutionary Developmental Biology, Gremlin, Gene Duplication
12 Sep 2016
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Lecture 6: Evolutionary Developmental Biology 10/13/2015
Evo-Devo
• Interdisciplinary approach
o Paleontology, anatomy, developmental biology, molecular
biology, genetics
• Attempts to explain rapid development of new body plans
Homeotic Genes
• aka Hox genes
• Control development
• Can be specific to regions of the body
Hox Genes and Body Complexity
• More Hox genes should allow for more axes of development
o Different genes for
▪ Up/down
▪ Forward/back
▪ Left/right
• Different Hox genes can control development of specific parts of the
body
o Front, middle, back
• Gene duplication mutations produce more Hox genes
o Paralogs
• Prediction: more complex organisms have more Hox genes
o True to an extent
Mutations that Affect Hox Gene Expression
• Hox genes have their own regulatory genes
• These are genes that turn on Hox genes
• Vary if or when a particular Hox gene is turned on
• Can result in
o Changes in structure
o Existing structures not to form
o Existing structures to form in new places
Example: Ubx gene and abdominal leg growth
• Mutation in Ubx gene inhibits d-11 gene which causes legs to grow
find more resources at oneclass.com
find more resources at oneclass.com
Example: Ubx gene and thoracic wing growth
• Deletion of ubx gene causes wing to grow on third thoracic segment
Variation in Spatial Expression of Developmental Genes
• Changes in when and where regulatory genes are expressed
• Can lead to big changes in structure
• Clawed vs webbed feet in fowl
o Both chicken and duck feet webbed as embryos
o BMP4—gene that causes tissue to degenerate (apoptosis)
o Gremlin gene produces protein to inhibit BMP4
o Presence of gremlin results in webbed feet
• Allometric Growth
o Differences in growth rates
o Example: chimp vs. human skull
o Genes promoting skull growth suppressed as chimp grows
o Genes promoting jaw growth continue
o Result: larger brain cavity in human adults
• Hoxc6
o In the mouse embryo, the transition form cervical to thoracic
vertebrae in the spine occurs at the anterior limit of Hoxc6
expression
o In the chicken, the anterior limit of Hoxc6 expression is
further down the spine, resulting in more cervical vertebrae
• Paedomorphosis
o Retention of larval/juvenile characteristics in adult
o Can lead to new body plans
o Examples:
▪ Copepod crustaceans
▪ lancelets
Fin vs. limb bud growth in vertebrates
• Both mouse limbs and fish fins form from limb buds in embryo
• Hoxd-11 and shh are both genes that regulate the direction of limb
bud growth
• Fish fin only express hoxd-11 and shh in rear of limb bud and early
find more resources at oneclass.com
find more resources at oneclass.com
