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Dialogue: 0,0:00:14.74,0:00:16.72,Default,,0000,0000,0000,,These days scientists know how you inherit
Dialogue: 0,0:00:16.72,0:00:18.47,Default,,0000,0000,0000,,characteristics from your parents.
Dialogue: 0,0:00:18.47,0:00:19.97,Default,,0000,0000,0000,,They are able to calculate probabilities
Dialogue: 0,0:00:19.97,0:00:21.19,Default,,0000,0000,0000,,of having a specific trait
Dialogue: 0,0:00:21.19,0:00:22.48,Default,,0000,0000,0000,,or getting a genetic disease
Dialogue: 0,0:00:22.48,0:00:23.71,Default,,0000,0000,0000,,according to the information they have
Dialogue: 0,0:00:23.71,0:00:25.77,Default,,0000,0000,0000,,from the parents and the family history.
Dialogue: 0,0:00:25.77,0:00:27.79,Default,,0000,0000,0000,,But how is this possible?
Dialogue: 0,0:00:27.79,0:00:29.11,Default,,0000,0000,0000,,To understand how traits pass
Dialogue: 0,0:00:29.11,0:00:31.34,Default,,0000,0000,0000,,from one living being to its descendants,
Dialogue: 0,0:00:31.34,0:00:33.51,Default,,0000,0000,0000,,we need to go back in time to the 19th century
Dialogue: 0,0:00:33.51,0:00:35.76,Default,,0000,0000,0000,,and a man named Gregor Mendel.
Dialogue: 0,0:00:35.76,0:00:37.89,Default,,0000,0000,0000,,Mendel was an Austrian monk and biologist
Dialogue: 0,0:00:37.89,0:00:39.56,Default,,0000,0000,0000,,who loved to work with plants.
Dialogue: 0,0:00:39.56,0:00:40.51,Default,,0000,0000,0000,,By breeding the pea plants
Dialogue: 0,0:00:40.51,0:00:42.14,Default,,0000,0000,0000,,he was growing in the monastery's garden,
Dialogue: 0,0:00:42.14,0:00:44.84,Default,,0000,0000,0000,,he discovered the principals that rule heredity.
Dialogue: 0,0:00:44.84,0:00:46.32,Default,,0000,0000,0000,,In one of most classic examples,
Dialogue: 0,0:00:46.32,0:00:48.69,Default,,0000,0000,0000,,Mendel combined a pure-bred, yellow-seeded plant
Dialogue: 0,0:00:48.69,0:00:50.70,Default,,0000,0000,0000,,with a pure-bred, green-seeded plant,
Dialogue: 0,0:00:50.70,0:00:52.78,Default,,0000,0000,0000,,and he got only yellow seeds.
Dialogue: 0,0:00:52.78,0:00:55.15,Default,,0000,0000,0000,,He called the yellow-colored trait the dominant one
Dialogue: 0,0:00:55.15,0:00:57.51,Default,,0000,0000,0000,,because it was expressed in all the new seeds.
Dialogue: 0,0:00:57.51,0:01:01.31,Default,,0000,0000,0000,,Then he let the new yellow-seeded hybrid plants self-fertilize.
Dialogue: 0,0:01:01.31,0:01:02.54,Default,,0000,0000,0000,,And in this second generation,
Dialogue: 0,0:01:02.54,0:01:04.43,Default,,0000,0000,0000,,he got both yellow and green seeds,
Dialogue: 0,0:01:04.43,0:01:06.09,Default,,0000,0000,0000,,which meant that the green trait had been hidden
Dialogue: 0,0:01:06.09,0:01:07.47,Default,,0000,0000,0000,,by the dominant yellow.
Dialogue: 0,0:01:07.47,0:01:10.01,Default,,0000,0000,0000,,He called this hidden trait the recessive trait.
Dialogue: 0,0:01:10.01,0:01:11.42,Default,,0000,0000,0000,,From those results, Mendel inferred
Dialogue: 0,0:01:11.42,0:01:13.93,Default,,0000,0000,0000,,that each trait depends on a pair of factors,
Dialogue: 0,0:01:13.93,0:01:15.10,Default,,0000,0000,0000,,one of them coming from the mother
Dialogue: 0,0:01:15.10,0:01:17.10,Default,,0000,0000,0000,,and the other from the father.
Dialogue: 0,0:01:17.10,0:01:19.06,Default,,0000,0000,0000,,Now we know that these factors are called alleles
Dialogue: 0,0:01:19.06,0:01:21.52,Default,,0000,0000,0000,,and represent the different variations of a gene.
Dialogue: 0,0:01:21.52,0:01:23.02,Default,,0000,0000,0000,,Depending on which type of allele
Dialogue: 0,0:01:23.02,0:01:24.44,Default,,0000,0000,0000,,Mendel found in each seed,
Dialogue: 0,0:01:24.44,0:01:26.27,Default,,0000,0000,0000,,we can have what we call a homozygous pea,
Dialogue: 0,0:01:26.27,0:01:27.98,Default,,0000,0000,0000,,where both alleles are identical,
Dialogue: 0,0:01:27.98,0:01:29.62,Default,,0000,0000,0000,,and what we call a heterozygous pea,
Dialogue: 0,0:01:29.62,0:01:31.53,Default,,0000,0000,0000,,when the two alleles are different.
Dialogue: 0,0:01:31.53,0:01:34.34,Default,,0000,0000,0000,,This combination of alleles is known as genotype
Dialogue: 0,0:01:34.34,0:01:36.37,Default,,0000,0000,0000,,and its result, being yellow or green,
Dialogue: 0,0:01:36.37,0:01:38.03,Default,,0000,0000,0000,,is called phenotype.
Dialogue: 0,0:01:38.03,0:01:39.93,Default,,0000,0000,0000,,To clearly visualize how alleles are distributed
Dialogue: 0,0:01:39.93,0:01:41.01,Default,,0000,0000,0000,,among its descendants,
Dialogue: 0,0:01:41.01,0:01:43.48,Default,,0000,0000,0000,,we can use a diagram called the Punnett Square.
Dialogue: 0,0:01:43.48,0:01:45.15,Default,,0000,0000,0000,,You just place the different alleles on both axes
Dialogue: 0,0:01:45.15,0:01:47.60,Default,,0000,0000,0000,,and then you figure out the possible combinations.
Dialogue: 0,0:01:47.60,0:01:49.49,Default,,0000,0000,0000,,Let's look at Mendel's peas, for example.
Dialogue: 0,0:01:49.49,0:01:52.82,Default,,0000,0000,0000,,Let's write the dominate yellow allele as an upper-case "Y"
Dialogue: 0,0:01:52.82,0:01:55.19,Default,,0000,0000,0000,,and the recessive green allele as a lower-case "y".
Dialogue: 0,0:01:55.19,0:01:58.19,Default,,0000,0000,0000,,The upper-case Y always overpowers his lower-case friend,
Dialogue: 0,0:01:58.19,0:01:59.61,Default,,0000,0000,0000,,so the only time you get green babies
Dialogue: 0,0:01:59.61,0:02:01.98,Default,,0000,0000,0000,,is if you have lower-case y's.
Dialogue: 0,0:02:01.98,0:02:03.32,Default,,0000,0000,0000,,In Mendel's first generation,
Dialogue: 0,0:02:03.32,0:02:04.82,Default,,0000,0000,0000,,the yellow, homozygous pea mom
Dialogue: 0,0:02:04.82,0:02:07.24,Default,,0000,0000,0000,,will give each pea kid a yellow, dominant allele,
Dialogue: 0,0:02:07.24,0:02:08.95,Default,,0000,0000,0000,,and the green, homozygous pea dad
Dialogue: 0,0:02:08.95,0:02:10.50,Default,,0000,0000,0000,,will give a green, recessive allele.
Dialogue: 0,0:02:10.50,0:02:13.21,Default,,0000,0000,0000,,So, all the pea kids will be yellow, heterozygous.
Dialogue: 0,0:02:13.21,0:02:14.92,Default,,0000,0000,0000,,Then, in the second generation,
Dialogue: 0,0:02:14.92,0:02:16.74,Default,,0000,0000,0000,,where the two heterozygous kids marry,
Dialogue: 0,0:02:16.74,0:02:19.95,Default,,0000,0000,0000,,their babies could have any of the three possible genotypes,
Dialogue: 0,0:02:19.95,0:02:21.20,Default,,0000,0000,0000,,showing the two possible phenotypes
Dialogue: 0,0:02:21.20,0:02:23.78,Default,,0000,0000,0000,,in a three-to-one proportion.
Dialogue: 0,0:02:23.78,0:02:25.91,Default,,0000,0000,0000,,But even peas have a lot of characteristics.
Dialogue: 0,0:02:25.91,0:02:27.58,Default,,0000,0000,0000,,For example, besides for being yellow or green,
Dialogue: 0,0:02:27.58,0:02:29.47,Default,,0000,0000,0000,,peas can be round or wrinkled,
Dialogue: 0,0:02:29.47,0:02:31.33,Default,,0000,0000,0000,,so we could have all these possible combinations:
Dialogue: 0,0:02:31.33,0:02:32.24,Default,,0000,0000,0000,,round yellow peas,
Dialogue: 0,0:02:32.24,0:02:32.100,Default,,0000,0000,0000,,round green peas,
Dialogue: 0,0:02:32.100,0:02:33.82,Default,,0000,0000,0000,,wrinkled yellow peas,
Dialogue: 0,0:02:33.82,0:02:35.47,Default,,0000,0000,0000,,and wrinkled green peas.
Dialogue: 0,0:02:35.47,0:02:38.06,Default,,0000,0000,0000,,To calculate the proportions of each genotype and phenotype,
Dialogue: 0,0:02:38.06,0:02:39.60,Default,,0000,0000,0000,,you can use a Pennett Square too.
Dialogue: 0,0:02:39.60,0:02:42.08,Default,,0000,0000,0000,,Of course, this will make it a little more complex.
Dialogue: 0,0:02:42.08,0:02:44.60,Default,,0000,0000,0000,,And lots of things are more complicated than peas,
Dialogue: 0,0:02:44.60,0:02:46.33,Default,,0000,0000,0000,,like, say, people.
Dialogue: 0,0:02:46.33,0:02:48.11,Default,,0000,0000,0000,,These days scientists know a lot more
Dialogue: 0,0:02:48.11,0:02:49.58,Default,,0000,0000,0000,,about genetics and heredity.
Dialogue: 0,0:02:49.58,0:02:50.62,Default,,0000,0000,0000,,And, there are many other ways
Dialogue: 0,0:02:50.62,0:02:52.53,Default,,0000,0000,0000,,in which some characteristics are inherited.
Dialogue: 0,0:02:52.53,0:02:54.57,Default,,0000,0000,0000,,But, it all started with Mendel and his peas.