Evolution of genetic networks/development (L17)

Exam 3 Lecture 17

Complex Adaptations

• Phenotypic traits that require multiple mutations to yield an advantage

Ex: Snake Venom

Regulatory Network

• A system of interacting genes, transcription factors, RNA, and other molecules

• Functions like a circuit, controlling the activation of genes during cellular development and the activation of metabolic pathways

Hox Genes

• Transcription factor genes

• Genes that specify segment identity/where a segment will form

• clustered in one spot

Drosophila

• fruit flies

• 8 hox genes in a row

• lab - at the 3’ end, expressed in the head

• Abd-B - at the 5’ end, expressed in the abdomen

• Dll / Distalless - production of antennae and legs

• htx / homothoroax - represses Dll in the abdomen

Antennapdia

• A homeotic transformation in fruit flies (one body part develops into another)

• caused by knocking out Hox genes

• Deleting Hox genes toward the 3’ end has more drastic effects

Promiscuous proteins

• Proteins that can carry out 2 functions

• prone to taking on new functions if duplicated

Paralog

A homologous gene that arises via gene duplication

Gene recruitment

• A gene/network being co-opted for a new function as a result of a mutation / placement of a new gene under a foreign regulatory system

• Reorganizing a preexisting regulatory network can lead to major evolution

E coli. LTEE

• Tracking genetic change in 12 E.coli colonies since 1988

• In 2003, one population evolved the ability to feed on citrate in the presence of oxygen - Caused by the duplication of the citT gene and its rnk promoter

Snake venom

• Crotamine genes are closely related to bacteria-fighting molecules in vertebrates

• Duplication and then evolution of the defensin gene caused proteins to move from the pancreas to the mouth, becoming venom

• Venom evolved before snakes

Spinal cord

Vertebrates- In the dorsal side

Annelids + Arthropods - In the ventral side

Apical Ectodermal Ridge

• In fish

• Hoxa11 and Hoxd13 overlap to stimulate the distal growth of the limb bones in the fin

• Once expression of Hox ceases, fin rays grow from the limb bones

• Not present in tetrapods

Zebrafish

• Experience pleiotropy with the Hoxd13 gene

• If expressed later in development, the outer area of the fin shrinks and the region where bone grows in the fin expands

Opsins

• Captures light in the eye

• proteins that bind to light-reactive chemicals

• helps guide vision, circadian rhythm, and other light-mediated responses

• Evolved in a common ancestor 1 bya

Crystallins

• Directs incoming light in the eye

• water-soluble, structural protein that accounts for transparency

• evolved through gene recruitment

Antagonistic pleiotropy

A mutation of a gene has positive effects for one trait but negative effects for another.

Cervical Vertebrae

• Almost every mammal has 7 cervical vertebrae

• Sloths have 8 and manatees have 6

• Being born with an extra vertebra makes you super likely to die

Convergent evolution

• Similar traits evolving independently in 2 unrelated lineages

• Ex: Flying squirrels and sugar gliders

Parallel evolution

• Similar traits evolving independently in lineages related by a common ancestor

• Ex: Cacti and Euphorbia

Deep Homology

When the growth/development of traits in different lineages results from underlying mechanisms from a common ancestor