The video addresses the concern of a potential decline in redhead genetics, explaining the science behind the transmission of the red hair gene. Despite sensationalized headlines about redhead extinction, the video clarifies that red hair genes can lie dormant for generations. By using examples and genetic principles such as Punnett squares, the video reassures viewers that red hair will persist through generations.

The video covers basic genetic concepts including genes, alleles, genotypes, and phenotypes. It explains how genetic traits are passed down through generations, influenced by both genetic coding and environmental factors. By using examples like human red hair and cat fur length, it elaborates on dominant and recessive traits, homozygous and heterozygous gene configurations, and patterns of inheritance like Mendelian and incomplete dominance.

Main takeaways from the video:

Please remember to turn on the CC button to view the subtitles.

Key Vocabularies and Common Phrases:

1. syzygy [ˈsɪzɪdʒi] - (n.) - A rare alignment or combination of voting different parties or elements. - Synonyms: (alignment, conjunction, meeting)

Literal ginger syzygy and it meets up with a second red haired gene variant.

2. phenotype [ˈfiːnəˌtaɪp] - (n.) - The set of observable characteristics of an individual resulting from the interaction of its genotype with the environment. - Synonyms: (appearance, characteristic, trait)

Meanwhile, the phenotype describes all the traits that we can observe in an organism.

3. genotype [ˈdʒiːnəˌtaɪp] - (n.) - An organism's complete set of genetic material, including variations in genes. - Synonyms: (genes, genetic makeup, hereditary)

We call an organism's complete collection of alleles its genotype, which Accounts for its entire genetic makeup.

4. alleles [əˈliːlz] - (n.) - Different versions of a gene, which can dictate distinct traits. - Synonyms: (variants, types, forms)

You see, each gene comes in different versions called alleles, which determine an organism's different traits.

5. heterozygous [ˌhɛtəroʊˈzaɪɡəs] - (adj.) - Having two different alleles for a particular gene. - Synonyms: (mixed, hybrid, crossbred)

That makes him heterozygous, which means he carries two different alleles for the hair lengths gene.

6. homozygous [ˌhoʊmoʊˈzaɪɡəs] - (adj.) - Having two identical alleles for a particular gene. - Synonyms: (purebred, uniform, consistent)

But fluffy Bagel has two recessive alleles, so she's homozygous.

7. autosomal dominance [ɔːtəˈsoʊməl ˈdɑːmɪnəns] - (n.) - A pattern of inheritance where a dominant allele completely masks the presence of a recessive one. - Synonyms: (Mendelian inheritance, dominant trait, genetic dominance)

When one allele completely overrides the other, we call that autosomal dominance.

8. codominance [koʊˈdɑːmɪnəns] - (n.) - A form of inheritance where two alleles are both fully expressed in the phenotype. - Synonyms: (dual dominance, equality, balance)

Sometimes, instead of mixing together, traits linked to two alleles show up separately in what's called co dominance.

9. chromosomes [ˈkroʊməˌsoʊmz] - (n.) - Long strands of DNA containing genetic material in the nucleus of cells. - Synonyms: (genes, DNA strands, genetic chains)

chromosomes are the long strands of genetic material in our cell nuclei.

10. incomplete dominance [ɪnˌkɑːmˈpliːt ˈdɑːmɪnəns] - (n.) - A genetic situation in which one allele does not completely dominate another, often resulting in a blend of traits. - Synonyms: (partial dominance, merging, blending)

Sometimes one allele doesn't completely overshadow the other, and instead they blend together and we what we call incomplete dominance.

Intro to Genetics - Why Your Cat Looks Like That - Crash Course Biology #31

Are we in the middle of a redhead mass extinction? Headlines like this tend to surface every few years, fretting that the rare ginger genes are getting rarer. But are we really watching the final embers of the fiery haired flame? Well, hold on to your Ed Sheerans. Rumors of their demise have been greatly exaggerated. Sure, if you could pull a hundred random strangers into a room, it's likely only a few of them will have red hair. And true red hair mostly happens only when a baby gets two copies of the red hair gene variant, which, yeah, it's pretty rare.

But good news, the gene variant also exists in people without red hair. In fact, it can pass on hidden for generations until the stars align. Literal ginger syzygy and it meets up with a second red haired gene variant. That's why sometimes two non redheads can have a baby with the shock of flaming hair. And unless every single person with the gene variant vanishes, the redheads of the world aren't going anywhere. We know this thanks to the study of how genes get passed down across generations. And a healthy understanding of how this happens can help us avoid these kinds of sensationalized stories.

That's right. Today we're breaking out our Punnett squares and talking about genetics. Hi, I'm Dr. Sammy, your friendly neighborhood entomologist. And this is crash course biology Ed Reba Flo. Y'all gonna hit us with that funky fame music. So let's talk about genes. Sorry, not those genes. These genes individualized sections of DNA on the chromosomes of cells. chromosomes are the long strands of genetic material in our cell nuclei. Typically, humans have 46 in total, or 23 pairs of two. But genes are the segments along those chromosomes that are used to carry instructions.

Humans have over 20,000 spread across our 46 chromosomes. Every living thing has them, and some weigh more than others, like the nearly microscopic freshwater flea, which clocks its gene count at over 30,000. Most genes carry specific instructions for making molecules called proteins. When those instructions get read in a process called gene expression, they shape how an organism looks and functions. You see, each gene comes in different versions called alleles, which determine an organism's different traits, like the shape of a seed or a person's blood type. Whenever we talk about versions or variants of genes, we're talking about alleles. Scientists just tend to use the phrases interchangeably. And the reason we don't all look like clones of each other is that we all have different versions of the same genesthese alleles.

We call an organism's complete collection of alleles its genotype, which Accounts for its entire genetic makeup. Meanwhile, the phenotype describes all the traits that we can observe in an organism. So your genotype might include the alleles for both a long big toe and a short big toe, but you present with a short big toe, so that's the one that's part of your phenotype. Most traits are determined by more than one gene. Like there's no single gene out there that determines the shape of your nose or your height. Those traits arise from several different alleles interacting with each other like a bunch of protein making puppeteers, which I guess sorta makes us all elaborate muppets, which I'm cool with, by the way. I mean, can you tell me how to get. How to get to Sesame Street? How to get to Sesame Street?

So it's not exactly like that, my desire to meet Elmo aside. But it is true that not every gene gets expressed in every cell. Cells are always collaborating and communicating, Making sure that the right genes turn on in the right place. And while the stuff going on inside is important, factors outside the body, like the environment, can also affect an organism's traits. Take the buckeye butterfly for example. Buckeyes that hatch during the long summer days have light tan wings as part of their phenotype. But those that hatch during shorter fall days have darker red wings. See the darker wings of autumn. Buckeyes absorb heat, raising their body temperature so that they can still fly, While lighter wings help the summer babies stay cool.

Buckeyes alleles contain the potential for both shades, but their environment, specifically the temperature and day length when they're born, shapes how those genes are expressed. Now, because humans and a lot of other species reproduce sexually, the offspring's genetic code ends up a unique mix of their parents. That's what happens when an egg and a sperm come together, each containing one set of all of their parents genes, One allele for each, so that they end up with two alleles for each gene. Sorry if that ruined any illusions of stork based baby delivery for you. The offspring inherits a unique combination of alleles from both parents.

Same genes, but different versions and different chromosomes of a matching pair and the interactions of those alleles. In many cases, the organism's environment affect the traits that ultimately get expressed. We call the way traits pass from generation to generation patterns of inheritance. Most traits come together almost like mosaics from multiple genes interacting with the environment. But some are determined by simpler patterns. Take for example, the length of a cat's fur. It's determined by a single gene called fibroblast growth factor 5 or FGF5. There are a number of allele variants of FGF5, including four different long hair alleles. But to keep it simple, today we'll lump them together as one. Think of this big L here as a short hair allele and it's what we call dominant.

When the two alleles meet, the dominant allele is the loudest, so it drowns out the little L here, which is the recessive long hair allele. It only takes one dominant allele for a cat to have short hair. But for long hair, a cat needs two quieter recessive copies. When one allele completely overrides the other, we call that autosomal dominance. You might also hear this called Mendelian inheritance, named after Gregor Mendel, a monk who first described this pattern in pea plants over 150 years ago. So let's take a look at how this pattern of inheritance actually works.

Meet Mortimer. He has short hair, white markings like a tuxedo, and loves long naps in the sun. A real prince, this guy. And this is Bagel. She's got long orange fur, razor sharp claws and a penchant for spilling coffee on keyboards. You wouldn't believe how many electronics she's destroyed, how much blood we've lost, or how much we love her. Anyway, opposites attract. And we happen to know Mortimer has one dominant short hair allele masking one long hair allele. That makes him heterozygous, which means he carries two different alleles for the hair lengths gene. But fluffy Bagel has two recessive alleles, so she's homozygous.

Genetics speak for samesies having two matching alleles, either both recessive or both dominant. And because we know our cats genotypes, we can predict the genotypic and phenotypic ratios of their hypothetical kittens. That's their probability of inheriting different allele combinations and therefore having long locks versus sleek fur. We can map out the odds with this chart called a punnett Square. There's a 50% chance that Mortimer and Beigel's kitten will inherit one copy of each allele, making it heterozygous dominant. The dominant big L talks over the recessive little L, giving it a short hair phenotype. You wouldn't even know the kitten has the long hair allele by looking at it. But there's also a 50% chance that a kitten turns out homozygous recessive, inheriting a little L from Bagel and a little L from mortimer, putting a 100% chance of floof in the forecast. But if Mortimer has two copies of the dominant allele, then there's no way around it.

This kitten will be bound for short hair. Sometimes one allele doesn't completely overshadow the other, and instead they blend together and we what we call incomplete dominance. This can lead to an expressed trait that's a mix of the traits associated with each allele. Like, let's say that the white in Mortimer's little tuxedo and Bagel's socks are determined by an incompletely dominant allele. For white spots, a cat with the big S alleles will be mostly covered in white. But in a heterozygous cat with just one copy, the white patches will cover less than half of his body. And since Mortimer and Bagel are both heterozygous for spots, their Kitten has a 25% chance of inheriting two dominant alleles and being mostly white.

The same odds of inheriting two recessive alleles and being spotless. But if I were a gambler, I'd put my bet on it being heterozygous like his parents. There's a 50% chance of that and a 100% chance of it being adorable. Sometimes, instead of mixing together, traits linked to two alleles show up separately in what's called co dominance. Kind of like wearing a Hawaiian shirt in a sequined jumpsuit. They're both jostling for attention. Calico cats, with their blotches of orange and black fur owe their look in part to CO dominance. But they've got another pattern of inheritance going on at the same time called sex linked inheritance. That's where a gene is carried only on one of the chromosomes that influences an organism's sex.

For most mammals, chromosomes come in two, X or Y. But a cool and important thing to know is that XY is not the only system out there. And some organisms don't have sexes at all anyway. In the XY system, an organism with two X chromosomes usually develops as female, while an organism with an X and a Y usually develops as male. So when a gene shows up on the X chromosome and not on the Y chromosome, its traits will show up at different rates in females and males. Now back to those calico kitties. A color gene on a cat's X chromosome comes in two alleles, an orange version and a black version. If a kitten inherits both alleles, each cell only expresses one at a time, so the fur ends up looking like Joseph's Technicolor dream code.

It's more straightforward for the XY carrier who gets only one X chromosome. Inherit one allele and it's orange fur. Inherit the other and it's black. That's why calico cats are almost always xx, and while co dominance isn't always dependent on sex, it is the case for calico kitties. There is so much that we can learn by studying genetics. It helps us understand how traits are passed from parent to offspring, why some cats are orange and others are black, and why we don't have to worry about running out of redheads anytime soon.

But it also helps us on a much larger scale, from creating more sustainable agriculture to designing better medicine. Our genes are the first gift that our parents ever gave us, instructions that made you you, and we can trace some basic patterns of inheritance by understanding how dominant and recessive alleles interact. But it goes even deeper than that. Most traits aren't just a matter of one allele talking over another. They're the result of an ongoing conversation between the stuff in your chromosomes and the stuff around them. Multiple alleles, multiple genes, and your whole environment. But we'll learn more about that next time. Peace.

Genetics, Inheritance, Science, Education, Innovation, Biology, Crashcourse