Evolutionary Development: Chicken Teeth - Crash Course Biology #17

CrashCourse
21 May 201210:57
EducationalLearning
32 Likes 10 Comments

TLDRThe video explains evolutionary developmental biology, which studies genes that control embryo development to understand evolution. It reveals animals have more genetic similarity than expected. Regulatory genes dictate when other genes activate, controlling body plan and identity. Differences across species are mostly in regulatory genes higher up the chain. The video explores an experiment where fruit fly genes, when triggered in the wrong place, still built a fly eye. This shows how small regulatory gene changes can drive big evolutionary leaps. Finally, it describes chick embryos growing ancestral dinosaur teeth, demonstrating how evolutionarily lost traits can reemerge when ancient genes activate.

Takeaways
  • 😊 Humans share 85% of their genes with mice, more than you might expect based on appearances.
  • 😮 Early developmental genes dictate basic body plans across species while later, more specialized genes control the details.
  • 🧬 Regulatory genes control when and how much other genes activate, orchestrating embryonic development.
  • 😲 Small mutations in regulatory genes can drive big evolutionary changes over relatively short timespans.
  • 🔬 Evolutionary developmental biology explores these genes to unravel mysteries of evolution and development.
  • 😃 Kids envision scientists doing wild experiments, but reality is more controlled than comic books.
  • 😜 Crazy experiments like adding eyeballs to fruit fly butts do occasionally happen though.
  • 😡 Birds have latent genes for teeth from their dinosaur ancestors that can randomly reemerge.
  • 🤯 Single regulatory gene mutations likely explains rapid dinosaur-to-bird evolution.
  • 🤓 There is still much to uncover about gene regulation, inheritance, and activation.
Q & A

  • What are developmental regulatory genes and what do they do?

    -Developmental regulatory genes are genes that control the identity and organization of body parts. They activate other genes that are responsible for actually building the body parts.

  • How similar genetically are humans and mice?

    -Humans and mice are 85% genetically identical.

  • What causes the differences in appearance between humans and mice despite genetic similarities?

    -The differences are caused by developmental regulatory genes lower down the chain of command that give more specific instructions. The high-level instructions are very similar between humans and mice.

  • How did researchers make a fruit fly with eyes on its legs?

    -They took a mouse gene that said "eye goes here" and activated it in the region where the fruit fly's legs develop. This caused the fruit fly to develop fly eyes next to its legs.

  • How do regulatory genes help explain evolution happening quickly?

    -Small changes in regulatory genes can lead to big changes in an organism's structure, allowing evolution to happen much faster than through gradual genetic mutations alone.

  • Why don't birds have teeth?

    -Mutations in regulatory genes likely shut off the genes for making enamel and dentin. So birds still have the genes for teeth from dinosaur ancestors, but they are not expressed.

  • How do we know birds still have genes for teeth?

    -Some mutant chickens were observed forming little teeth. Mutations had allowed the previously repressed teeth genes to become expressed again.

  • What activates the first developmental regulatory genes?

    -We don't fully know yet. Scientists think regulatory proteins made by earlier genes and present in the egg may help activate the first genes.

  • Are regulatory genes inherited differently than other genes?

    -Most regulatory genes seem to be inherited the same way, but some very early ones may have their proteins already present in the egg to kickstart development.

  • Why don't regulatory genes have different alleles?

    -There is strong selection pressure to keep the regulatory genes the same within a species so that all individuals develop the proper basic body plan.

Outlines
00:00
🧪 How kids imagine being scientists vs reality

The paragraph discusses how kids have fanciful ideas about being a scientist, like creating human-animal hybrids or getting superpowers. But real science doesn't usually involve crazy experiments like that. The paragraph then introduces the field of evolutionary developmental biology, which studies how genes control body plan development and is providing insights into evolution.

05:01
😴 How genes control embryo development

This paragraph provides more details on developmental genes, which control when and where body parts form in embryos. It discusses different tiers of regulatory genes, with master control genes at the top that initiate body part identity and lower genes that provide more specific instructions. The paragraph also notes that while the function of regulatory genes is known, how they are first activated remains a mystery.

10:02
👀 Making a fruit fly with eyeballs on its butt

The paragraph describes an experiment where scientists inserted a mouse gene that controls eye development into fruit fly DNA. This caused the flies to develop eyes on their hindlegs rather than mouse eyes, demonstrating how regulatory genes control overall body plan while lower genes handle the specifics. This helps explain how evolution can sometimes happen rapidly.

Mindmap
Keywords
💡developmental regulatory genes
These are genes that control the timing and location of the activation of other genes during embryonic development. They are like architects that lay out the body plan, telling other genes when and where to activate to build body parts. Changes in these top-level regulatory genes can lead to big evolutionary changes in body structure, like dinosaurs losing teeth and evolving beaks to become birds.
💡hox genes
Hox genes are a specific class of developmental regulatory genes that control body segmentation and identity of body parts during embryonic development. They set up the basic body plan and identify where to put key features like legs, eyes, etc. Small mutations in hox genes can lead to big changes in body structure over evolutionary time.
💡fruit fly
Fruit flies are model organisms frequently used in biological experiments because they reproduce rapidly and have well-understood genetics. In this video, fruit fly embryos were genetically modified to activate fly eye-forming genes in the region that becomes the fly's back leg, causing a fly eye to develop on the leg.
💡vestigial structures
Vestigial structures are body parts or features that organisms evolved in ancestral species but are no longer useful or expressed in modern species. However, the genes for these features can reappear if the developmental genes that repress them become mutated. Examples discussed include bird embryos regrowing dinosaur-like teeth and snakes being born with vestigial limbs.
💡beak
Beaks are a key feature that evolved in theropod dinosaurs as they transitioned into modern birds. Evo-devo reveals that birds lost teeth via changes to regulatory genes, not gradual mutation of tooth-building genes. Their beaks formed from upregulation of keratin genes that formerly made scales.
💡genetic similarity
The video explains that humans share over 85% genetic similarity with mice, not just the 98.6% shared with chimps. Similarities in crucial developmental regulatory genes and body segmentation amongst all mammals account for major common features despite outward differences.
💡embryonic development
The complex process by which a fertilized egg grows into a mature organism. Developmental regulatory genes control this process by coordinating timing and body locations for activation of genes that build body parts. Slight errors in this precisely regulated process can lead to birth defects.
💡evolution
The process by which populations of organisms change over generations to adapt to their environment. Evo-devo provides insight into evolution by showing how small mutations in key regulatory genes during embryonic development can lead to major morphological changes as species adapt.
💡fossil record
The fossilized remains of ancient organisms that show evolutionary relationships and adaptations over geological timescales. By comparing fossils to modern species, scientists can trace evolutionary changes. Rapid dinosaur/bird transition revealed timing issue with gradual gene mutation theories of evolution.
💡gene expression
Whether and how much a gene is activated to produce its products such as proteins that carry out biological functions. Regulatory genes control gene expression of downstream targets. Repressed gene expression, not gradual mutation, accounts for loss of traits like dinosaur teeth in birds.
Highlights

Evolutionary developmental biology looks at genes to understand how body parts develop and how evolution happens.

All animals are much more genetically similar than previously thought - humans and mice are 85% the same.

Developmental regulatory genes control when and where body parts form by activating other genes.

Hox genes determine the identity and organization of body parts by directing where to put things like legs and tails.

There is a hierarchy of genes where regulatory genes sit at the top sending instructions down to genes that do more specific tasks.

Regulatory genes tend to be nearly identical within a species, providing the same basic blueprint for the organism.

The big picture regulatory genes controlling basic features are similar across vertebrates, which is why humans and mice share 85% DNA.

Adding a regulatory gene to fruit fly DNA that said "make an eye here" resulted in a fruit fly eye developing where it shouldn't.

Small mutations in regulatory genes can drive big evolutionary changes in body structure over a relatively short time.

Birds lost teeth not through gradual mutation but by changes to regulatory genes shutting off tooth production.

Ancient ancestral features like teeth can reappear if the genes for them are turned back on through mutations to regulators.

The ability for major changes to happen quickly through regulators helps explain puzzles in the fossil record.

Chickens were found to grow teeth after mutations affected their regulatory genes.

Other examples exist of ancestral features reappearing, like snakes born with legs.

This emerging science around developmental genes and evolution is opening new frontiers of understanding.

Transcripts

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