1 00:00:01,920 --> 00:00:06,400 Speaker 1: Welcome to brain Stuff, a production of iHeart Radio. Hey 2 00:00:06,440 --> 00:00:09,639 Speaker 1: brain Stuff, Lauren Bogel bum here. You may have heard 3 00:00:09,640 --> 00:00:11,920 Speaker 1: that a hundred and thirty seven is the magic number, 4 00:00:12,240 --> 00:00:14,720 Speaker 1: but if you ask a geneticist, they'll tell you that 5 00:00:14,760 --> 00:00:18,599 Speaker 1: the real magic is in forty six. Why forty six 6 00:00:19,040 --> 00:00:22,400 Speaker 1: because that's the total number of chromosomes found in most 7 00:00:22,520 --> 00:00:26,160 Speaker 1: every human cell, twenty three pairs to be exact, and 8 00:00:26,400 --> 00:00:29,840 Speaker 1: those little red like structures pack all the information about 9 00:00:29,880 --> 00:00:33,960 Speaker 1: who you are and what makes you unique. To understand 10 00:00:34,000 --> 00:00:37,479 Speaker 1: what chromosomes are, first, we have to understand what DNA is. 11 00:00:37,920 --> 00:00:41,400 Speaker 1: Formally known as de oxy ribonucleic acid, DNA is a 12 00:00:41,400 --> 00:00:45,000 Speaker 1: complex molecule found in all plants and animals. It's found 13 00:00:45,040 --> 00:00:47,760 Speaker 1: in almost every cell of an organism's body, and it 14 00:00:47,800 --> 00:00:51,199 Speaker 1: contains all of the information necessary to keep that organism 15 00:00:51,280 --> 00:00:55,680 Speaker 1: up and running and developing and reproducing. DNA is also 16 00:00:55,720 --> 00:00:59,680 Speaker 1: the primary way that organisms pass on hereditary information and 17 00:00:59,760 --> 00:01:02,600 Speaker 1: the access of reproduction. A portion of DNA is passed 18 00:01:02,640 --> 00:01:06,360 Speaker 1: along from parent to offspring. In short, DNA is what 19 00:01:06,520 --> 00:01:11,080 Speaker 1: tells the story of your totally unique biology. As you 20 00:01:11,120 --> 00:01:14,319 Speaker 1: can probably imagine, DNA has to be pretty long to 21 00:01:14,360 --> 00:01:18,240 Speaker 1: hold all of that important information, and it is. If 22 00:01:18,240 --> 00:01:21,200 Speaker 1: you stretched the DNA and just one cell all the 23 00:01:21,240 --> 00:01:23,280 Speaker 1: way to its full length, it would be about six 24 00:01:23,280 --> 00:01:25,960 Speaker 1: and a half feet or two meters long. And if 25 00:01:26,000 --> 00:01:28,720 Speaker 1: you put the DNA and all your cells together, you'd 26 00:01:28,720 --> 00:01:33,840 Speaker 1: have a chain about twice the diameter of the solar system. Luckily, 27 00:01:34,000 --> 00:01:37,160 Speaker 1: cells are pretty smart and have an ingenious way of 28 00:01:37,200 --> 00:01:42,199 Speaker 1: packaging all that info into space efficient parcels. Enter the chromosome, 29 00:01:43,280 --> 00:01:45,760 Speaker 1: with its name rooted in the Greek words for color 30 00:01:45,880 --> 00:01:50,120 Speaker 1: chroma and body soma. The chromosome is a cell structure 31 00:01:50,360 --> 00:01:53,280 Speaker 1: or body that scientists can spot under a microscope by 32 00:01:53,280 --> 00:01:57,400 Speaker 1: staining it with colored dyes and get it. Each chromosome 33 00:01:57,480 --> 00:02:00,080 Speaker 1: is made up of protein and YEP d n A. 34 00:02:01,280 --> 00:02:05,280 Speaker 1: Every chromosome contains exactly one molecule of DNA to be exact, 35 00:02:05,600 --> 00:02:08,760 Speaker 1: and that long string of genetic info is tightly wrapped 36 00:02:08,760 --> 00:02:11,600 Speaker 1: around the protein called a his stone, which acts like 37 00:02:11,639 --> 00:02:15,640 Speaker 1: a spool, efficiently bundling the lengthy info rich molecule into 38 00:02:15,680 --> 00:02:18,040 Speaker 1: the perfect size and shape to fit inside the nucleus 39 00:02:18,080 --> 00:02:21,520 Speaker 1: of a cell. Human cells typically have twenty three pairs 40 00:02:21,520 --> 00:02:24,800 Speaker 1: of chromosomes for a total of forty six aside from 41 00:02:24,840 --> 00:02:27,440 Speaker 1: sperm and egg cells, which each contain only half of 42 00:02:27,440 --> 00:02:31,600 Speaker 1: that that's twenty three chromosomes. The magic number of forty 43 00:02:31,639 --> 00:02:34,640 Speaker 1: six or twenty three pairs of chromosomes per cell isn't 44 00:02:34,720 --> 00:02:38,639 Speaker 1: universal among living things. Of first, humans happen to be 45 00:02:38,680 --> 00:02:41,839 Speaker 1: a diploid species, which means that most of our chromosomes 46 00:02:41,880 --> 00:02:45,240 Speaker 1: come in matched sets called homologous pairs. The two members 47 00:02:45,280 --> 00:02:48,560 Speaker 1: of each pair are called homologus. A lot of animals 48 00:02:48,560 --> 00:02:51,120 Speaker 1: and plants are diploid, but not all of them have 49 00:02:51,320 --> 00:02:55,040 Speaker 1: a total number of forty six chromosomes. Mosquitoes, for example, 50 00:02:55,240 --> 00:02:59,560 Speaker 1: have a diploid chromosome number of six, frogs have twenty six, 51 00:02:59,800 --> 00:03:03,160 Speaker 1: and to shrimp have a whopping five hundred and eight chromosomes. 52 00:03:04,200 --> 00:03:07,360 Speaker 1: But why do humans have twenty three pairs? It happened 53 00:03:07,440 --> 00:03:11,200 Speaker 1: during evolution. For the article, this episode is based on 54 00:03:11,320 --> 00:03:14,639 Speaker 1: How Stuff Works. Spoken by email with Berlin Hurley, PhD, 55 00:03:14,919 --> 00:03:17,919 Speaker 1: a research fellow at the National Human Genome Research Institute 56 00:03:18,000 --> 00:03:21,720 Speaker 1: at the National Institutes of Health. She said humans have 57 00:03:21,800 --> 00:03:25,520 Speaker 1: twenty three pairs of chromosomes, while all other great apes, chipanzees, 58 00:03:25,560 --> 00:03:30,000 Speaker 1: Bonnabo's guerrillas, and orangutans have twenty four pairs of chromosomes. 59 00:03:30,200 --> 00:03:34,080 Speaker 1: This is because in the human evolutionary lineage, two ancestral 60 00:03:34,120 --> 00:03:38,440 Speaker 1: ape chromosomes fused at their telomeres or tips, producing human 61 00:03:38,520 --> 00:03:43,000 Speaker 1: chromosome two. Thus, humans have one fewer pair of chromosomes. 62 00:03:43,320 --> 00:03:45,320 Speaker 1: This is one of the main differences between the human 63 00:03:45,360 --> 00:03:50,160 Speaker 1: genome and the genome of our closest relatives. Now let's 64 00:03:50,200 --> 00:03:53,480 Speaker 1: get back to that sperm and egg issue. These cells 65 00:03:53,520 --> 00:03:56,960 Speaker 1: only have one homologous chromosome from each pair and are 66 00:03:57,000 --> 00:04:02,120 Speaker 1: therefore considered haploid. Here's why. When a sperm and egg fuse, 67 00:04:02,320 --> 00:04:05,960 Speaker 1: they combine their genetic material to form one complete diploid 68 00:04:06,080 --> 00:04:08,880 Speaker 1: set of chromosomes. And if you think about it, that 69 00:04:08,960 --> 00:04:12,280 Speaker 1: makes perfect sense. It means each parent contributes one set 70 00:04:12,360 --> 00:04:16,679 Speaker 1: to a pair of chromosomes in their child cells. Consider 71 00:04:16,720 --> 00:04:19,880 Speaker 1: blood type as a clear example. People with a B 72 00:04:19,880 --> 00:04:23,280 Speaker 1: blood type inherited two different gene variations on their two 73 00:04:23,279 --> 00:04:27,159 Speaker 1: homologous chromosomes, one for A and one for B that 74 00:04:27,480 --> 00:04:32,360 Speaker 1: when combined, produced a B Okay, So twenty three pairs 75 00:04:32,360 --> 00:04:35,679 Speaker 1: of chromosomes is typical for humans. But life doesn't always 76 00:04:35,720 --> 00:04:38,679 Speaker 1: go by the book. So what happens if something causes 77 00:04:38,720 --> 00:04:42,360 Speaker 1: more or fewer chromosomes to develop. A gain or loss 78 00:04:42,360 --> 00:04:45,640 Speaker 1: of chromosomes from these standard forty six is called an euploidy, 79 00:04:45,920 --> 00:04:48,720 Speaker 1: and it can occur either during the formation of reproductive 80 00:04:48,760 --> 00:04:51,920 Speaker 1: cells the sperm in the egg, or in early fetal development, 81 00:04:52,360 --> 00:04:54,679 Speaker 1: or in any other cell of the body after birth. 82 00:04:55,839 --> 00:04:58,640 Speaker 1: One of the most common forms of antiploidy is trisome, 83 00:04:58,920 --> 00:05:01,560 Speaker 1: which is the presence of an extra chromosome in the cells. 84 00:05:02,200 --> 00:05:05,400 Speaker 1: One well known result of trisome is Down syndrome, which 85 00:05:05,480 --> 00:05:08,279 Speaker 1: is a condition caused by three copies of chromosome twenty 86 00:05:08,320 --> 00:05:11,640 Speaker 1: one in each cell. This extra chromosome leads to a 87 00:05:11,680 --> 00:05:15,239 Speaker 1: total of forty seven chromosomes per cell rather than forty six. 88 00:05:16,600 --> 00:05:19,479 Speaker 1: The loss of one chromosome in a cell is called monosomey. 89 00:05:19,920 --> 00:05:22,280 Speaker 1: That's when people have just one copy of a specific 90 00:05:22,320 --> 00:05:26,880 Speaker 1: chromosome per cell as opposed to two. For example, Turner syndrome, 91 00:05:26,960 --> 00:05:29,160 Speaker 1: in which women have only one copy of the X 92 00:05:29,240 --> 00:05:32,359 Speaker 1: chromosome per cell versus the regular two, is a form 93 00:05:32,440 --> 00:05:37,960 Speaker 1: of monosomey. There are other variations of ante eploidy as well, 94 00:05:38,279 --> 00:05:42,800 Speaker 1: and in extreme cases, they may compromise a person's life. Additionally, 95 00:05:42,920 --> 00:05:46,320 Speaker 1: cancer cells also have alterations in their number of chromosomes. 96 00:05:46,960 --> 00:05:50,400 Speaker 1: Unlike the variations that happen in reproductive cells, these changes 97 00:05:50,480 --> 00:05:58,440 Speaker 1: cannot be inherited. Today's episode is based on the article 98 00:05:58,560 --> 00:06:01,360 Speaker 1: why do most humans have three pairs of chromosomes? On 99 00:06:01,520 --> 00:06:05,360 Speaker 1: how stuff works dot Com written by Michelle Konstantinovski. Brain 100 00:06:05,400 --> 00:06:07,640 Speaker 1: Stuff is production of I Heart Radio in partnership with 101 00:06:07,640 --> 00:06:10,320 Speaker 1: how stuff works dot Com and is produced by Tyler Clang. 102 00:06:10,800 --> 00:06:13,200 Speaker 1: Four more podcasts my heart Radio, visit the I heart 103 00:06:13,240 --> 00:06:15,800 Speaker 1: Radio app, Apple Podcasts, or wherever you listen to your 104 00:06:15,800 --> 00:06:16,480 Speaker 1: favorite shows.