Pax 6 information for essay

Whats the difference between upstream vs downstream mechanisms?

While the upstream master regulatory Pax6 switch remains universal, the morphological downstream genes have diverged to produce species specific optics.

Remember:

The Switch (Pax6) is Homologous (Deep Homology).

The Structures (Lens & Retina) are Convergent (Analogous).

Describe the Gehring experiment (Gehring 1996)

• Action: He took the Mouse Pax6 gene and inserted it into the genome of a Fruit Fly embryo. He "switched on" the mouse gene in the cells destined to become the fly's legs, wings, and antennae.

• Result: The fly grew fully formed eyes on its legs and antennae

How does Gehring experiment explain master control genes?

The Gehring experiment highlights the hierarchical nature of development. Pax6 acts as a Selector Gene at the top of a Gene Regulatory Network (GRN). Its ability to initiate the fly's compound-eye program using a mouse-derived signal proves that Pax6 specifies location and identity, while the actual morphological execution is handled by specific downstream genes.

How is Gehring experiment example of co-option?

Rather than inventing a new trigger for every eye type, evolution has conserved a single 'Master Switch' (Pax6). This allows for modularity: the 'switch' remains the same, while the 'machinery' it recruits (lenses, opsins, crystallins) can be co-opted and specialized for different environments

Explain functional segregation link?

Before complex eyes existed, the common ancestor of all Bilaterians likely had a multi-functional cell. This single cell had to do two jobs:

1)Sense light using Opsins and 2) Provide shade using Pigment (melanin) so the animal could tell which direction the light was coming from.

Over time this cell underwent functional segregation where the cell lineage split into two specialized types:

The Photoreceptor Cell: Lost its pigment and became highly specialized for capturing photons using Opsins.

The Pigment Cell: Lost its opsins and became specialized for shading the photoreceptor forming the Retinal Pigment Epithelium

Explain evolution of eye lens in terms of co-option?

The evolution of the eye lens is a primary example of convergent co-option, where different phyla recruited locally available proteins to serve as crystallins. In mammals, for instance, ancestral heat shock proteins were co-opted to form alpha-crystallins within the lens. These proteins were selected by evolution due to their intrinsic stability, transparency, and high solubility, which allow them to be densely packed to provide refractive power without clumping. This co-option was achieved through two key regulatory shifts: heterotopy, where a change in the spatial domain caused these proteins to be expressed in the eye instead of their original tissues, and heterometry, where the proteins were massively over-expressed to reach the high concentrations required to form a functional lens.

How do we know its convergence not homology?

As different species use different proteins to form eye lens for example humans co-opted heat shock proteins whereas squid co-opted metabolic enzymes

If the lens were homologous, they would use the same protein. Because they use different ones, we know the lens evolved convergently.

How does inverted vs everted eye structure provide evidence of convergence?

Even when two animals evolve the same Camera eye type they often do it differently.

Humans have an Inverted Retina where nerves sit in front of our photoreceptors. Light has to pass through the nerves to hit the sensors.

Octopuses have an Everted Retina. Their nerves sit behind the photoreceptors. They have no blind spot.

f the camera eye were homologous, we would share the same "wiring" layout. The fact that our wiring is "backwards" compared to an octopus proves that we evolved camera eyes independently.

What is Anomalocaris link?

The antiquity of the eye-building toolkit is underscored by the fossil record of the Cambrian predator Anomalocaris. Possessing sophisticated compound eyes with over 16,000 lenses, Anomalocaris demonstrates that the Pax6-driven Gene Regulatory Network was capable of producing high-acuity vision as early as 515 million years ago.

What is link to plant evolution?

The conservation of master regulators like Pax6 in animals and the KNOX-ARP module in plants provides profound support for François Jacob’s view of evolution as a 'tinkerer. Just as the 'switch' for eye development remained fixed while the 'factory' of downstream genes was modified to produce diverse optics, the plant KNOX pathway was repurposed to define the boundaries between stems and leaves.