Lecture Three: Evolution Video, HOX Genes, Nervous System and Brain, Fish Flashcards
January 30
What new features does an internal skeleton allow for?
Sensory systems on the outside of the body.
More mobility (flexible).
What did the first major predators have? What does this imply?
Eyes. Implies they have a complex brain to process visual information. However, this does not mean they had a tripartite brain.
An early scorpion (like shown in the video) would not be able to go through ecdysis on land. Why?
Land was hot! Scorpion would have dried out.
The exoskeleton is what allowed movement on land. If the exoskeleton was shed, the organism wouldn’t really have been able to move.
What do HOX genes do?
Help lay out the basic body forms of many animals. Set up head-to-tail orientation.
(Also found in plants)
What are HOX genes? How are they arranged?
Transcription factors that use a particular DNA binding motif (homeobox). They initiate the expression of OTHER genes that bring about the body form.
Found in clusters and expressed colinearly.
How do HOX genes act?
Produce proteins in a developing embryo.
These proteins act at the tip of a developmental cascade that tuns on their target genes by binding to very specific DNA sequences preceding other gene codes.
Thus, they cause target genes to produce new proteins themselves.
Neurons:
Individual cells that form the basic unit of the nervous system.
Myelin Sheath:
Fatty insulating coat that surrounds the axon of neurons and serves to increase the conduction velocity of the nerve impulse.
Axon:
Long extension of the neuron.
Nerve:
A collection of axons.
Dendrite:
Branched process that extends from a nerve cell to connect to other neurons.
What differentiates vertebrate nerve cells from invertebrate nerve cells?
Myelin sheaths.
Despite having no myelin sheaths, invertebrate nerve cells can transmit signals as quickly as vertebrate nerve cells. How?
They increase the diameter of their nerve cells.
What is a benefit of myelin sheaths (other than transmission speed)?
Allow nerves to be smaller, thus enabling more to be packed into a smaller area.
What does the forebrain do?
Receives and integrates sensory information from the nose, eyes, and ears.
What does the midbrain do?
Coordinates reflex responses to sights and sounds.
What does the hindbrain do?
Controls reflexes, respiration, circulation, and other basic tasks.
How did the functionally distinct regions of vertebrate brains arise?
Expansion and modification of the dorsal nerve cord.
What are the two parts of the hindbrain and what do they do?
- Metencephalon: Regulates motor activity
- Myelencephalon (medulla oblongata): Regulates respiration, balance, and orientation.
What was the earliest “definite” vertebrate?
Ostracoderms (there were many different types of these). They were JAWLESS! (Like lamprey). Jaws came later.
Other than being vertebrates, what was unique about ostracoderms?
First emergence of bone in the form of a head shield. Internal bones were not yet in play (internal skeleton was cartilaginous).
What significant group followed the ostracoderms? What change happened in between?
Chondrichthyes (cartilaginous fish).
Emergence of jaws.
(Placoderms could also be a contender for first to have jaws. This group is fully extinct).
Bony endoskeletons did not truly appear until the emergence of what group?
Osteichthyes (bony fish).
What are the different types of gnathostome teeth?
- Tooth whorl: each tooth is independent and can always be replaced. (Likely only found in cartilaginous fish).
- Pleurodont: Teeth sit in a groove along the jaw.
- Acrodont: Teeth are fused to the jaw.
- Thecodont: Teeth sit inside a socket and are held in place by a ligament (soft tissue). We have this.
