What Darwin Never Knew (NOVA) Part 4/8 HD

Summary

The script explores the fascinating world of genetic diversity in animals, highlighting how similar sets of genes can produce vastly different physical traits. It delves into the work of Sean Carroll, who studies the genetic 'switches' that activate or deactivate genes, leading to variations like wing spots in fruit flies. The script also discusses the implications of these genetic mechanisms in evolutionary processes, such as the loss of limbs in whales, manatees, and snakes, and the potential discovery of a common genetic switch behind these adaptations.

Takeaways

• 🧬 All animals use a similar set of key genes to build their bodies, known as body plan genes, which determine the placement and form of body parts like heads, limbs, and wings.
• 🦓 Another set of genes is responsible for an animal's body patterning, such as blotches, stripes, and spots, and these same genes can be found in various creatures from leopards to peacocks to fruit flies, producing different results.
• 🔬 The number of genes is not as crucial as how they are used, which is the key to the diversity seen in the animal kingdom.
• 🧪 Sean Carroll's research focuses on understanding how the same genes are used to create diversity, using the fruit fly as a model organism due to its simplicity and ease of study.
• 🕺 The male fruit fly performs a courtship dance to attract females, showcasing wing spots that are important for mating success.
• 🌀 The 'paintbrush gene' codes for black wing spots, but its presence alone does not guarantee spots; it's how the gene is used that matters.
• 🔍 Carroll discovered that a stretch of non-coding DNA, referred to as a 'switch,' can turn the paintbrush gene on or off, leading to the presence or absence of wing spots in different species of fruit flies.
• ✨ The switch is a powerful part of DNA that controls where and when genes are activated, influencing the physical traits of animals without changing the genes themselves.
• 🐟 The loss of traits, such as legs in snakes or whales, can be linked to the action of genetic switches, which turn off the genes responsible for those traits.
• 🦴 Researchers found a link between the loss of stickleback fins and the mutation of a switch that controls the activation of the gene responsible for the fins.
• 🧬 The study of genetic switches is helping to solve evolutionary puzzles, such as how different species have evolved to lose certain body parts, and it may provide insights into the broader patterns of evolution.

Q & A

What is the key insight about animal evolution that modern biologists have discovered?

The key insight is that it's not the number of genes that counts, but how these genes are used that generates the great diversity of the animal kingdom.

What role do body plan genes play in the development of animals?

Body plan genes determine where the head, limbs go and what form they take, whether they are arms, legs, or wings.

What is the significance of the 'paintbrush gene' mentioned in the script?

The 'paintbrush gene' codes for the black wing spots in certain species of fruit flies, and its presence or activation can determine the appearance of these spots.

Why are fruit flies considered an unlikely hero in modern science?

Fruit flies are considered an unlikely hero because they are small, inexpensive, and reproduce quickly, making them ideal for laboratory studies despite their simplicity.

What is the role of non-coding DNA in the evolution of animal bodies?

Non-coding DNA, once considered 'junk,' contains regulatory elements or 'switches' that can turn genes on and off, influencing the physical characteristics of animals.

How did Sean Carroll's experiment with the unspotted fly and the jellyfish gene demonstrate the concept of genetic switches?

By injecting a combination of the non-coding DNA stretch found in the spotted fly and a glowing gene from a jellyfish into the unspotted fly, Carroll showed that the non-coding DNA acted as a switch to activate the 'paintbrush gene,' causing the unspotted fly's wings to glow with spots.

What is the connection between the stickleback fish and the broader understanding of evolutionary processes?

The stickleback fish provides an example of how genetic switches can turn off certain genes, like those responsible for the defensive spikes, leading to the evolution of different species in different environments.

Why are the findings on the stickleback fish significant for understanding the evolution of other animals like manatees and whales?

The findings suggest that similar genetic switches might be responsible for the loss of limbs in different animals, providing a potential explanation for the evolution of streamlined bodies in aquatic and slithering creatures.

What is the significance of the lopsided pattern found in the stickleback fish and manatee skeletons?

The lopsided pattern suggests that the same genetic switch might be involved in the loss of hind limbs in different species, indicating a common evolutionary mechanism.

How does the script illustrate the importance of studying simple organisms to understand complex biological phenomena?

By using the fruit fly and stickleback fish as model organisms, the script shows how studying these simple creatures can reveal fundamental principles of genetics and evolution that apply to more complex organisms.

What are the implications of understanding genetic switches for the field of evolutionary biology?

Understanding genetic switches can help solve perplexing evolutionary questions, such as how one creature can evolve into another with different physical characteristics, by shedding light on the mechanisms that control gene expression during development.

Outlines

00:00

🌱 The Genetic Basis of Animal Diversity

This paragraph delves into the fascinating world of biological diversity, highlighting how various animals, despite their differences, utilize the same set of key genes to develop their bodies. These 'body plan' genes dictate the placement and form of body parts like heads and limbs, which can manifest as arms, legs, or wings. Another set of genes is responsible for an animal's body patterning, such as spots and stripes, and is present in creatures from leopards to peacocks to fruit flies, producing diverse outcomes. The insight that the number of genes isn't as crucial as their usage in generating diversity is emphasized. The work of Sean Carroll is introduced, who studies the genetic machinery behind wing spots in fruit flies, using them as a model to understand broader evolutionary processes. The discovery that both spotted and non-spotted fruit flies possess the 'paintbrush' gene responsible for wing spots, but use it differently, leads to the exploration of how genetic 'switches' in non-coding DNA regions can activate or suppress gene expression, thus driving physical variations among species.

05:00

🔍 Unraveling the Mystery of Genetic 'Switches'

The second paragraph focuses on the discovery and significance of genetic 'switches' in understanding evolutionary changes in animal bodies. Sean Carroll's research on fruit flies with and without wing spots led to the identification of a non-coding DNA stretch that acts as a switch to turn the 'paintbrush' gene on or off, controlling wing spot formation. This segment of DNA, when introduced into the non-spotted fly, activated the gene, causing glowing spots to appear, demonstrating the power of these switches in gene regulation. The concept of switches is expanded to explain broader evolutionary phenomena, such as the loss of legs in snakes, whales, and manatees, suggesting a connection between the genetic mechanisms underlying these changes. The paragraph also hints at the potential for switches to play a role in the evolution of other physical traits, beyond the examples provided.

10:07

🧬 The Evolutionary Impact of Genetic Switches

This paragraph continues the exploration of genetic switches, discussing their role in the evolution of physical traits in various species. The research of David Kingsley and Dolph Schluter on sticklebacks, which have evolved differently in lake and ocean environments, is highlighted. They identified a gene responsible for the defensive belly spikes in ocean sticklebacks and found it to be identical in lake sticklebacks, which lack these spikes. The discovery of a mutated section of DNA in the lake sticklebacks, which acts as a broken switch preventing the gene's activation, is a significant finding. The researchers propose that this mechanism could be linked to the loss of hind limbs in other animals, such as manatees, and suggest that the same genetic switch might be responsible for these evolutionary changes. The paragraph concludes by posing a broader question about the role of switches in shaping the diverse forms and patterns observed in the animal kingdom.

Keywords

💡Diversity

Diversity in this context refers to the variety of life forms and their physical characteristics within the animal kingdom. It is a central theme of the video, illustrating how a limited set of genes can produce a vast array of species with different appearances and functions. The script mentions that modern biologists are fascinated by the diversity of animals despite their underlying genetic similarities.

💡Body Plan Genes

Body plan genes are the set of genes that determine the basic structural organization of an organism, including where the head, limbs, and other body parts are located. They are crucial for understanding how different animals develop their unique body structures. The script explains that these genes dictate the placement and form of features like arms, legs, or wings across various species.

💡Gene Expression

Gene expression is the process by which the genetic information stored in DNA is converted into functional products, such as proteins. It is key to understanding how the same genes can result in different physical traits in different species. The video emphasizes that it's not just the genes themselves but how they are expressed that leads to the diversity seen in the animal kingdom.

💡Peacock and Fruit Fly

The peacock and fruit fly are used in the script as examples to illustrate the principle of gene expression in creating diverse physical patterns. While the peacock is known for its colorful feathers, the fruit fly is highlighted for its role in scientific research, showing that even these small creatures have genes that produce varied patterns like blotches, stripes, and spots.

💡Evolution

Evolution is the process by which species change over time through genetic variation and natural selection. The script discusses how understanding gene expression and switches has advanced our knowledge of how evolutionary changes, such as the loss of limbs in certain animals, occur.

💡Paintbrush Gene

The 'paintbrush gene' is a term used in the script to describe a specific gene responsible for creating black wing spots in certain fruit flies. The discovery that this gene is present in both spotted and unspotted fruit flies highlights the importance of gene regulation rather than gene presence for physical traits.

💡Genetic Switch

A genetic switch, as mentioned in the script, is a segment of DNA that controls the activation or deactivation of other genes. These switches are not genes themselves but regulate when and where genes are expressed. The video explains how mutations in these switches can lead to the development of new traits, such as the presence or absence of wing spots in fruit flies.

💡Non-Coding DNA

Non-coding DNA refers to the portions of the genome that do not code for proteins but still play regulatory roles, such as acting as genetic switches. The script points out that a significant portion of an organism's DNA is non-coding, and scientists like Sean Carroll are uncovering their importance in gene regulation and evolution.

💡Mutation

A mutation is a change in the DNA sequence that can result in alterations of an organism's traits. In the context of the video, a mutation in a genetic switch can cause a gene like the 'paintbrush gene' to be turned on or off, leading to the development of new species with different characteristics.

💡Sexual Selection

Sexual selection is a process where certain traits are favored in a species because they increase an individual's chances of mating success. The script describes how male fruit flies use a courtship dance and wing spots to attract females, illustrating how traits can evolve due to sexual selection.

💡Adaptation

Adaptation refers to the process by which organisms become better suited to their environment through genetic changes. The script discusses how various animals, like the stickleback fish, have adapted by losing certain features, such as belly spikes, which are no longer advantageous in their new environment.

Highlights

Diversity in animal bodies is not due to the number of genes but how they are used.

Body plan genes determine the placement and form of body parts like limbs and wings.

Different animals, from leopards to fruit flies, use the same genes for body patterning.

Sean Carroll's research focuses on understanding how the same genes create diversity in animal bodies.

The fruit fly is an important model organism for studying genetic mechanisms due to its simplicity.

Courtship behaviors, like the fruit fly's wing display, are influenced by genetic factors.

The 'paintbrush gene' codes for black wing spots but its presence alone does not guarantee spots.

Non-coding DNA, once considered 'junk', plays a crucial role in gene regulation.

A specific stretch of non-coding DNA acts as a 'switch' to turn genes on or off in certain areas of the body.

Switches are powerful DNA elements that control gene expression without coding for physical traits.

Mutations in DNA switches can lead to the creation of new species with distinct traits.

Evolutionary loss of traits, like snake legs, can be explained by the deactivation of certain genes.

The stickleback fish provides insights into how genetic switches can lead to the loss of physical features.

Researchers have identified a genetic switch linked to the loss of stickleback belly spikes in a freshwater environment.

The same genetic switch mechanism may be responsible for the loss of hind limbs in manatees and whales.

Remnants of lost features, like pelvic bones in manatees, may indicate the use of the same genetic switch across species.

The discovery of genetic switches advances our understanding of evolution and the development of diverse animal forms.

Transcripts

well diversity it is the platform for

diversity what fascinates modern

biologists is that all these different

animals don't just look the same they

are using virtually the same set of key

genes to build their bodies the body

plan genes determine where the head goes

where the limbs go and what form they

take whether they are arms legs or wings

another set of genes determines an

animal's body patterning the blotches

the stripes and spots it is the same

genes at work in every creature from the

leopard to the peacock to the fruit fly

and yet they produce radically different

results

this has led scientists to a crucial

insight about how animal bodies have

evolved it's not the number of genes

that counts it's not the genes you have

but how you use them that generates the

great diversity of the animal kingdom

finding out just how these same genes

are used to create such amazing

diversity has been the work of Sean

Carroll and an unlikely hero of modern

science the food fly as much as I'd like

to study the mammals of the African

savannah they make poor choices for

laboratory animals they're large

expensive then reproduce very slowly to

get data we have to find the simplest

examples of the phenomenon we understand

but the humble fruit fly does weird and

wonderful things

this fruit fly is dancing for sex a rapt

female takes in the show she's

particularly besotted by the dark spots

on the male's wings watching it all

isn't equally besotted Sean Carroll you

might think then just the annoying but

they're really charming and the male's

of this species does a rather elaborate

courtship dance where he displays these

spotted wings in front of the female to

us is as magnificent as what a peacock

does

but in some species of food fly the

males don't have wing spots there's

another fruit fly species that's

different from the spotted species in

two important ways it doesn't have spots

on its wings and it does a lot less

dancing here then is a classic

evolutionary puzzle why does one type of

fly have spots and the other doesn't

Sean Carroll wanted to know what is

going on in their genes that makes them

different so we wanted to take apart the

genetic machinery for making wings bus

to understand how those wing spots of

all Carroll began the process of sifting

through the two types of flies DNA he

had one clue to set him on his way he

already knew the gene that codes for the

black wing spots he calls it the

paintbrush gene but surprisingly when he

compared the genes of the two flies they

both had that gene and yet only one had

spots when we look at that gene in the

two species really they both have this

paintbrush gene so the big difference is

not having the gene it's how they use it

one species uses it in the wing to make

spots the other one doesn't

so why did the paintbrush gene create

spots in one type of fly but not in the

other in search of answers

Carol turned to one of the least

understood regions of DNA the vast

stretches that were once known as junk

it has been called the dark matter of

the genome mysterious uncharted strange

the vast bulk of the double helix some

98% of it doesn't code for proteins

which make the stuff of our bodies the

genes which do comprise just 2% even now

no one sure what much of this huge

non-coding area actually does but it has

long back and evolutionary detectives

like Sean Carroll Carroll had already

learned that the paintbrush gene itself

was identical in the two types of fly so

he extended his search through their DNA

and in one place just outside the

paintbrush gene he found an important

clue a stretch of DNA that was different

than the fly with wing spots

what could this mean

so Carol conducted an experiment so the

injecting Buddha Pharisee he decided to

put that mysterious stretch of DNA that

he found in the spotted fly in the

unspotted fly to help him see if it had

any effect he attached it to a gene from

a jellyfish a gene that codes for a

protein that makes the jellyfish glow we

cut the DNA up into little pieces and we

hook it up to a protein that glows in

the dark and then we inject that into

the unspotted fly and then something

remarkable happened we look at those

unspotted flies we see now their wings

are glowing in the dark with spots

somehow that mysterious stretch of DNA

had turned on the paintbrush gene in the

unspotted flies wings once spotless now

it had luminous spots bingo

we found the piece of DNA that mattered

Carol had found something that is

revolutionizing our understanding of how

different animal bodies have evolved a

piece of DNA called a switch

switches are not jeans they don't make

stuff like hair cartilage or muscle but

they turn on and off the genes that do

switches are very powerful parts of DNA

because they allow animals to use genes

in one place and not another at one time

and not another

and so choreograph the spots and stripes

and spots of animal bodies in the case

of the fruit fly it's a mutation a

change in just a few letters of the DNA

that has caused the paintbrush gene to

be switched on and so a whole new

species with wing spots has been created

but switches are now explaining far more

than that they are helping to solve many

perplexing evolutionary questions like

how one creature can become another

creature by losing its legs it all goes

back to what Darwin had seen in the

snake embryo the rudiments of leg bumps

this convinced him that a snake must

have evolved from some four-legged

animal over the years that same

mysterious process the losing of legs

has been seen in other creatures like

the whale its front flippers have all

the bones of a land creatures arm even

the fingers and further back in its body

it has the vestiges of a pelvis

clearly it is descended from an animal

that walked on the land lots of animals

have evolved to slither through the

ground like snakes other animals slither

or swim through the water like whales so

if you need a streamlined body it's good

to get rid of these things that stick

out from the body like limbs like the

whale the manatee is another huge mammal

that lives in the sea and it too has

lost its hind legs how

Darwyn could never have answered that

question but now thanks to our

understanding of how DNA is switched on

and off and a very small fish we are

getting a little closer in this lake in

British Columbia there's a creature that

really shouldn't be here

a stickleback most sticklebacks live in

the ocean but some 10,000 years ago a

few were left stranded in this lake cut

off from the Pacific and over the years

they have evolved

the ocean stickleback has a pair of fins

on its belly that are like spikes they

are for defense

the spikes make the stickleback hard to

eat but the lake sticklebacks have lost

those spikes on their bellies and it's

this that intrigues researchers David

Kingsley and his colleague Dolph

Schluter

to understand what's behind it they

first identified the gene that makes the

stickleback spikes it's one of those key

body plan genes and not surprisingly

they found it to be identical in both

the ocean and the lake stickleback the

question was why hadn't it been turned

on in the lake stickleback which had

lost its spikes Kingsley felt the answer

might lie in a switch we know these

genetic switches exist but they're still

very hard to find we don't have a

genetic code that lets us read along the

DNA sequence and say there's a switch to

turn a gene on in a particular place but

eventually coming through the vast

stretch of DNA that does not code for

proteins he found it a section of DNA

that had mutated in the lake stickleback

these mutations meant that the switch

was broken it didn't turn on the gene

that makes spikes but this work may have

implications far beyond sticklebacks

they are convinced that there is a link

between the stickleback losing its

spikes and other creatures like a

manatee losing their legs and they have

two tantalizing clues one the same body

plan gene that is responsible for the

stickleback spikes also plays a role in

the development of the hind limbs

the second clue is more tentative the

lake stickleback may have lost its

spikes but evolution has left behind

some tiny remnants the traces of bones

and they are lopsided bigger on the left

than on the right we thought wouldn't it

be amazing if in fact this classic

unevenness is the signature of using the

same gene to control hind limb loss in

incredibly different animal so Kingsley

and his team went looking in manatees

searching for this lopsided pattern and

they found it in box after box of

manatee skeletons they saw pelvic bones

that were bigger on the left and smaller

on the right right now Kingsley and his

team were looking for the same switch in

the manatee that caused the lake

stickleback to lose its spikes and if

they find it they will have a powerful

explanation for something that baffled

Darwin how creatures like manatees

whales and snakes can evolve away their

legs

but all this begs another question if

switches can play such a profound role

in the different shapes and patterns of