[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:06.98,0:00:10.72,Default,,0000,0000,0000,,It's often said that despite \Nhumanity's many conflicts,
Dialogue: 0,0:00:10.72,0:00:14.25,Default,,0000,0000,0000,,we all bleed the same blood.
Dialogue: 0,0:00:14.25,0:00:17.53,Default,,0000,0000,0000,,It's a nice thought\Nbut not quite accurate.
Dialogue: 0,0:00:17.53,0:00:21.54,Default,,0000,0000,0000,,In fact, our blood comes \Nin a few different varieties.
Dialogue: 0,0:00:21.54,0:00:25.27,Default,,0000,0000,0000,,Our red blood cells contain\Na protein called hemoglobin
Dialogue: 0,0:00:25.27,0:00:27.11,Default,,0000,0000,0000,,that binds to oxygen,
Dialogue: 0,0:00:27.11,0:00:30.33,Default,,0000,0000,0000,,allowing the cells to transport it\Nthroughout the body.
Dialogue: 0,0:00:30.33,0:00:33.25,Default,,0000,0000,0000,,But they also have another kind\Nof complex protein
Dialogue: 0,0:00:33.25,0:00:35.95,Default,,0000,0000,0000,,on the outside of the cell membrane.
Dialogue: 0,0:00:35.95,0:00:41.06,Default,,0000,0000,0000,,These proteins, known as antigens,\Ncommunicate with white blood cells,
Dialogue: 0,0:00:41.06,0:00:44.52,Default,,0000,0000,0000,,immune cells that protect \Nagainst infection.
Dialogue: 0,0:00:44.52,0:00:47.10,Default,,0000,0000,0000,,Antigens serve as identifying markers,
Dialogue: 0,0:00:47.10,0:00:51.12,Default,,0000,0000,0000,,allowing the immune system to recognize\Nyour body's own cells
Dialogue: 0,0:00:51.12,0:00:54.51,Default,,0000,0000,0000,,without attacking them as foreign bodies.
Dialogue: 0,0:00:54.51,0:00:59.53,Default,,0000,0000,0000,,The two main kinds of antigens, A and B,\Ndetermine your blood type.
Dialogue: 0,0:00:59.53,0:01:04.02,Default,,0000,0000,0000,,But how do we get four blood types\Nfrom only two antigens?
Dialogue: 0,0:01:04.02,0:01:08.84,Default,,0000,0000,0000,,Well, the antigens are coded for\Nby three different alleles,
Dialogue: 0,0:01:08.84,0:01:11.53,Default,,0000,0000,0000,,varieties of a particular gene.
Dialogue: 0,0:01:11.53,0:01:15.45,Default,,0000,0000,0000,,While the A and B alleles code\Nfor A and B antigens,
Dialogue: 0,0:01:15.45,0:01:18.67,Default,,0000,0000,0000,,the O allele codes for neither,
Dialogue: 0,0:01:18.67,0:01:22.42,Default,,0000,0000,0000,,and because we inherit \None copy of each gene from each parent,
Dialogue: 0,0:01:22.42,0:01:27.08,Default,,0000,0000,0000,,every individual has two alleles\Ndetermining blood type.
Dialogue: 0,0:01:27.08,0:01:28.85,Default,,0000,0000,0000,,When these happen to be different,
Dialogue: 0,0:01:28.85,0:01:33.61,Default,,0000,0000,0000,,one overrides the other \Ndepending on their relative dominance.
Dialogue: 0,0:01:33.61,0:01:39.83,Default,,0000,0000,0000,,For blood types, the A and B alleles\Nare both dominant, while O is recessive.
Dialogue: 0,0:01:39.83,0:01:45.78,Default,,0000,0000,0000,,So A and A gives you type A blood,\Nwhile B and B gives you type B.
Dialogue: 0,0:01:45.78,0:01:47.67,Default,,0000,0000,0000,,If you inherit one of each,
Dialogue: 0,0:01:47.67,0:01:52.52,Default,,0000,0000,0000,,the resulting codominance\Nwill produce both A and B antigens,
Dialogue: 0,0:01:52.52,0:01:54.45,Default,,0000,0000,0000,,which is type AB.
Dialogue: 0,0:01:54.45,0:01:56.83,Default,,0000,0000,0000,,The O allele is recessive,
Dialogue: 0,0:01:56.83,0:02:00.16,Default,,0000,0000,0000,,so either of the others will override it\Nwhen they're paired,
Dialogue: 0,0:02:00.16,0:02:03.32,Default,,0000,0000,0000,,resulting in either type A or type B.
Dialogue: 0,0:02:03.32,0:02:07.51,Default,,0000,0000,0000,,But if you happen to inherit two Os,\Ninstructions will be expressed
Dialogue: 0,0:02:07.51,0:02:12.85,Default,,0000,0000,0000,,that make blood cells \Nwithout the A or the B antigen.
Dialogue: 0,0:02:12.85,0:02:14.94,Default,,0000,0000,0000,,Because of these interactions,
Dialogue: 0,0:02:14.94,0:02:16.76,Default,,0000,0000,0000,,knowing both parents' blood types\N
Dialogue: 0,0:02:16.76,0:02:21.71,Default,,0000,0000,0000,,lets us predict the relative probability \Nof their children's blood types.
Dialogue: 0,0:02:21.71,0:02:23.54,Default,,0000,0000,0000,,Why do blood types matter?
Dialogue: 0,0:02:23.54,0:02:25.08,Default,,0000,0000,0000,,For blood transfusions,
Dialogue: 0,0:02:25.08,0:02:28.94,Default,,0000,0000,0000,,finding the correct one is a matter\Nof life and death.
Dialogue: 0,0:02:28.94,0:02:33.56,Default,,0000,0000,0000,,If someone with type A blood\Nis given type B blood, or vice versa,
Dialogue: 0,0:02:33.56,0:02:38.19,Default,,0000,0000,0000,,their antibodies will reject \Nthe foreign antigens and attack them,
Dialogue: 0,0:02:38.19,0:02:42.18,Default,,0000,0000,0000,,potentially causing \Nthe transfused blood to clot.
Dialogue: 0,0:02:42.18,0:02:46.74,Default,,0000,0000,0000,,But because people with type AB blood\Nproduce both A and B antigens,
Dialogue: 0,0:02:46.74,0:02:51.87,Default,,0000,0000,0000,,they don't make antibodies against them,\Nso they will recognize either as safe,
Dialogue: 0,0:02:51.87,0:02:54.31,Default,,0000,0000,0000,,making them universal recipients.
Dialogue: 0,0:02:54.31,0:02:55.53,Default,,0000,0000,0000,,On the other hand,
Dialogue: 0,0:02:55.53,0:02:58.100,Default,,0000,0000,0000,,people with blood type O\Ndo not produce either antigen,
Dialogue: 0,0:02:58.100,0:03:01.51,Default,,0000,0000,0000,,which makes them universal donors,
Dialogue: 0,0:03:01.51,0:03:04.37,Default,,0000,0000,0000,,but will cause their immune system\Nto make antibodies
Dialogue: 0,0:03:04.37,0:03:09.46,Default,,0000,0000,0000,,that reject any other blood type.
Dialogue: 0,0:03:09.46,0:03:13.68,Default,,0000,0000,0000,,Unfortunately, matching donors \Nand recipients is a bit more complicated
Dialogue: 0,0:03:13.68,0:03:16.31,Default,,0000,0000,0000,,due to additional antigen systems,
Dialogue: 0,0:03:16.31,0:03:18.31,Default,,0000,0000,0000,,particular the Rh factor,
Dialogue: 0,0:03:18.31,0:03:22.58,Default,,0000,0000,0000,,named after the Rhesus monkeys\Nin which it was first isolated.
Dialogue: 0,0:03:22.58,0:03:29.26,Default,,0000,0000,0000,,Rh+ or Rh- refers to the presence\Nor absence of the D antigen
Dialogue: 0,0:03:29.26,0:03:31.96,Default,,0000,0000,0000,,of the Rh blood group system.
Dialogue: 0,0:03:31.96,0:03:34.82,Default,,0000,0000,0000,,And in addition to impeding \Nsome blood transfusions,
Dialogue: 0,0:03:34.82,0:03:38.36,Default,,0000,0000,0000,,it can cause severe complications\Nin pregnancy.
Dialogue: 0,0:03:38.36,0:03:42.85,Default,,0000,0000,0000,,If an Rh- mother is carrying an Rh+ child,
Dialogue: 0,0:03:42.85,0:03:47.22,Default,,0000,0000,0000,,her body will produce Rh antibodies\Nthat may cross the placenta
Dialogue: 0,0:03:47.22,0:03:49.14,Default,,0000,0000,0000,,and attack the fetus,
Dialogue: 0,0:03:49.14,0:03:53.34,Default,,0000,0000,0000,,a condition known as \Nhemolytic disease of the newborn.
Dialogue: 0,0:03:53.34,0:03:57.09,Default,,0000,0000,0000,,Some cultures believe blood type\Nto be associated with personality,
Dialogue: 0,0:03:57.09,0:03:58.91,Default,,0000,0000,0000,,though this is not \Nsupported by science.
Dialogue: 0,0:03:58.91,0:04:01.40,Default,,0000,0000,0000,,And though the proportions\Nof different blood types
Dialogue: 0,0:04:01.40,0:04:03.78,Default,,0000,0000,0000,,vary between human populations,
Dialogue: 0,0:04:03.78,0:04:06.60,Default,,0000,0000,0000,,scientists aren't sure why they evolved;
Dialogue: 0,0:04:06.60,0:04:09.14,Default,,0000,0000,0000,,perhaps as protection \Nagainst blood born diseases,
Dialogue: 0,0:04:09.14,0:04:11.87,Default,,0000,0000,0000,,or due to random genetic drift.
Dialogue: 0,0:04:11.87,0:04:15.72,Default,,0000,0000,0000,,Finally, different species \Nhave different sets of antigens.
Dialogue: 0,0:04:15.72,0:04:19.68,Default,,0000,0000,0000,,In fact, the four main blood types\Nshared by us apes
Dialogue: 0,0:04:19.68,0:04:25.94,Default,,0000,0000,0000,,seem paltry in comparison \Nto the thirteen types found in dogs.