/ Birth Control / Blood Typing / Colorblindness / DNA / Glossary / Sex-Linked Diseases /
Meiosis is the process by which an organism creates sex cells--in humans, that would be sperm and eggs. In meiosis, every chromosome in the cell is copied--leaving you with 2 copies of each chromosome and therefore 4 of each homolog. The homologs then form tetrads, and crossing over occurs. The cell divides, resulting in two diploid cells. Each diploid cell divides again, resulting in four* haploid gametes. (*Note: In meiosis in females, only one of the four gametes is viable. The other three are polar bodies.) Here comes the sex part. (To keep this easier, I'll just explain this using humans... if you've come to read about birth control, I'm sure you don't care about how turnips reproduce.) During sexual intercourse, the male ejaculates inside the female and sperm swim through the cervix and into the womb, where an egg cell [sometimes] waits. if the sperm cell gets lucky, :) it penetrates the egg and deposits its DNA. The resulting cell is called a "zygote," and it contains DNA from both its mother and its father. The zygote then divides again and again and again, its cells becoming more and more specialized ("Okay, you're going to be a brain cell, and I'm going to be part of this guy's foot. That cell over there can be his liver, and that other one can be a lung cell.") until the fetus reaches maturity and is born. (Everyone knows all about giving birth, so I won't bother.)
Now that you know how babies are made, what do you do if you don't want a baby, but you still want to have sex? Well, there's this thing called "birth control," and I guarantee you that this is a good thing. However, you should be fully aware on not only the side effects and effectiveness of each method of birth control, but also the mechanisms by which the birth control works. (Yes, yes, I know, more science. But, if you're concerned about what you're really doing to your body, this is something you should know.)
Now, here's something I really want to get into. Pill vs. mini pill. Each has its benefits and its drawbacks, and I really think it's important to understand this. This will especially be of interest to those people (like me) who believe that life begins at conception. (If you don't believe this, don't hiss at me, but please at least hear me out on this one. I'm not going to discuss abortion here.) The pill works because it keeps your body from ovulating, and if you don't release an egg, then you can't get pregnant. So, this is why the pill is so effective: as long as you take your pills and you don't miss a day (this is critical; if you miss a day or two, everything will be completely thrown off) you will not get pregnant unless you are a complete freak of nature. (Which you aren't.) However, you have to realize that it is a really big deal not to ovulate. I don't even know how to begin to tell you how much it messes up your body not to ovulate. You're supposed to ovulate once a month, every month, from when you're about 12 (give or take, of course. I was 10, I've heard of people being 9 and 14, though... it really doesn't matter...) to about 35 years from then. It's an essential part of your biochemistry---if you suddenly stopped getting periods, you'd worry, wouldn't you? Well, you get periods because the lining of the uterus thickens so that a fertilized egg can attatch itself to it---if there's no egg, your body won't do it... unless you trick it with the hormones in the pill. Anyway, my point is that the pill messes you up.
The mini-pill, on the other hand, isn't as damaging biochemically. It works by preventing the implantation of the fertilized egg into the uterine lining---in other words, you still ovulate, and you technically still conceive, but the embryo never develops. This isn't a problem for a lot of people, I'm sure, but I'm appalled that anyone would ever dream of conceiving a child and then letting it die. Also remember that you're still giving yourself a dose of hormones with the mini-pill.
I've gone on and on long enough about reasons not to go on the pill, but, of course, if there weren't benefits far fewer women would be taking it. Generally, you take the pill in the morning and forget about it all day. You can have sex with whomever you want and not get pregnant. (Remember that I'm talking about protection against pregnancy, not sexually transmitted diseases, which I really don't want to discuss on my page...) I'll be really blunt about this. If you know you have a tendency to be really slutty, and you're smart enough to know that you don't want to support a child at this time in your life, IMHO the benefits of the pill (eg: NOT GETTING PREGNANT) outweigh the drawbacks. I do believe that no matter what it does to you, it's better to cause the harm to yourself than to conceive an unwanted child.
Blood Typing
Blood typing is awesome. If you don't know your blood type, it's a lot more fun to test your blood yourself than to
have a lab technician do it for you. (Assuming, of course, you've got the nerve to poke your finger.) If you don't know your
blood type and would like to find out, or if you do know your blood type but would still like to test it yourself, you can order
a home blood typing kit here. You'll probably discover that you're either O positive or A positive,
like most of the population. If you'd like to know how frequently each of the blood types is found, here's
the place to go. Despite the fact that the author misspelled "AIDS," the site gives a good explanation about why and how you should give blood.
Colorblindness
About 1 in 12 American males is colorblind. Most of them don't even know that they are. The thing is---most people who are colorblind still see color; it's just that they are unable to differentiate between some colors, such as red and green. A lot of colorblind people don't believe that they're colorblind for the same reason that people with normal color vision don't believe they're colorblind---they still see a multitude of colors! Here's a really cool thing... while colorblindness is really common in men, it's insanely rare in women. This is because the gene that allows us to see colors is located on the X-chromosome.
DNA
Deoxyribonucleic acid, more commonly known as DNA is the most amazing chemical in our bodies.
In fact, DNA is present in every organism... as well as many viruses. DNA is absolutely vital
to life, as it's a code that tells our cells what proteins to manufacture. The Human
Genome Project is a mass effort by molecular biologists to identify every protein normal human DNA codes for.
DNA is named after its chemical structure. It is a nucleic acid because it is an acid found in the nucleus of a cell. It is composed of a phosphate group, a monosaccharide, and a nitrogenous base. The monosaccharide in DNA is called deoxyribose, since it is nearly identical to the sugar ribose, except it is missing one oxygen atom. It is the nitrogenous bases, however, which code for the proteins. There are only four bases: adenine, thymine, guanine, and cytosine. A group of three nitrogenous bases is called a codon. Each codon codes for a specific amino acid. (Note: many amino acids have more than one codon, but each codon only has one amino acid)
Glossary
Sex-Linked Diseases
Sex-linked diseases seem really weird, but stem from a really cool concept. Women have two "X" chromosomes, and men have one "X" and one "Y". I put these in quotes because the X doesn't look like an X, and the Y doesn't look like a Y! And, another interesting piece of trivia for those of you who don't know, we have 23 pairs of chromosomes. Chromosomes are numbered from biggest to smallest... so if you hear something about "chromosome 1," that's the biggest human chromosome. (Chromosome 22, not 23, is considered the smallest, because pair #23 is the sex chromosomes.) The X chromosome is about as large as chromosome 12... it's literally an average-sized chromosome. The Y chromosome, however, is even smaller than chromosome 22... it's a scrawny little runt. (To any macho guys reading this--I'm not lying; it really is.) For those of you who, for whatever reason, don't believe me, you can take a look at a karyotype of a normal human male. Notice the relative sizes of the X and Y chromosomes. Now, if you're really skeptical and would like to compare the male karyotype with the female karyotype, click here. See. I wasn't lying to you after all.
Anyway, now that you've looked at the karyotypes, you've noticed that the Y chromosome is considerably smaller than the X. You would think that because it's so much smaller, it wouldn't be able to have as many genes as the X, and you would be right. The Y chromosome is missing tons of genes that the X has. Among these are the genes that allow for color vision and the production of hemoglobin. For this reason, a male is entirely dependent on his X chromosome for these genes. But women have X chromosomes, too... why would this be different? Well, here's where things get cool. Most sex-linked diseases are recessive, (there are also sex-linked dominant diseases, but I'll get into those later) so if you have a messed up version of the gene, you'll be fine, as long as you have a normal version. So, if a woman inherits an X chromosome that has a messed up hemoglobin gene, her other X chromosome will still be normal, and her blood will clot normally. If a male, however, inherits the same messed up X chromosome, he has no other X chromosome with the normal gene, so he is automatically a hemophiliac. I'm going to talk about hemophilia for a while, because it's easier to understand if you just think about one disease, but remember that this applies to any sex-linked recessive disease or disorder.
I have no idea what the frequency of hemophilia has, but let's assume that 1 in 500 males has the disease. (I'm sure the actual statistic is much lower.) A male always inherits the disease from his mother, because he gets his X chromosome from her. How do we know that he didn't get his X chromosome from his father? Simple. If he did, he would have been born a girl. :) Remember, a woman can only pass down an X, but a man can pass down an X or a Y. Consequently, men actually determine (not decide, determine) the sex of their offspring. This makes history a lot more ironic if you remember all of the monarchs who got really pissed at their wives didn't bear any sons... it was the kings who were to blame all along. Anyway, it used to be that women never got hemophilia, because a boy born with hemophilia would die from bleeding to death before he would reach maturity. As a result of modern technology, however, we can treat hemophilia and many hemophiliacs do live to reproduce. (Note: A female hemophiliac will NOT be able to reproduce, because birth is a bloody process. When a baby is born, its mother loses about thirteen ounces of blood. A hemophiliac mother would bleed to death. So, while their reproductive systems are fully functional, female hemophiliacs are not only unable to give birth, they have to have hormone therapies or hysterectomies to prevent them from even having periods, because they'd die from that, too. Does anyone else see the irony in this?) If a hemophiliac (remember, I'm talking about men now) reproduces, he will almost definitely have normal offspring. His Y chromosome doesn't have the gene, so his sons will be normal. His X chromosome is affected, but unless his wife is a carrier of the disease, his daughters will have normal blood and all will be well. Or will it? The carrier daughters have one normal X and one affected X... from now on, I'll notate the affected X by making it green. Anyway, the daughter marries a normal man, so their genotypes are XX and XY. Their offspring, then, can be XX, XX, XY, or XY. These genotypes would indicate, in order, a normal female, a carrier female, a normal male, and a hemophiliac male. Remember that these are only probabilities. If a carrier female conceives a child, there is a 25% chance of each of these outcomes. The odds are that if she has four children, she will have one of each type, but it is just as possible that they will all be unaffected females. Probability is not law. I'm getting off the topic, but here's an example. My mother has A blood, and she's carrying a recessive gene for O blood. My father has O blood. I have a brother and a sister. The odds are that one or two of my parents' children (me and my siblings) would have A blood, and one or two of us have O blood. But, we all have O blood. None of us inherited the gene for A blood. So, keep in mind that if a carrier woman had ten kids, they could all be normal, or (although this would be really rare) they could all have hemophilia. Anyway, look at this again. If a hemophiliac male lives to reproduce with a normal woman, half of the grandsons he has through his daughters will also have hemophilia. And so the legacy continues.
Let's go back to a previous scenario... remember how I said that the hemophiliac male has children with a normal woman? What if that woman's a carrier? Then, the possible genotypes of the children will be the following: XX, XX, XY, XY. Half of the children will have hemophilia, regardless of their genders. This can only happen when an affected man lives long enough to pass down crappy genes! The only children that will not be affected at all will be half of the sons---you'll know from the start which have hemo and which don't. If he gets cut and he doesn't die, he doesn't have the disease. Anyway, that's an EXTREMELY rare scenario; I seriously doubt that there have been more than maybe 3 women with hemophilia ever born. Try not to worry about it too much.
Another interesting thought... some people have extra sex chromosomes. In other words, there are XXY males, XYY males, XXX females, XXXX females, XXXY males, XYYY males, etc. (If an individual has a Y chromosome, regardless of the number of X chromosomes, he will be male.) There are even XO females, who are missing an X chromosome. I'll get into that one later, too. Anyway, as I was saying, if a male has an extra X chromosome, he can have a sex-linked disease and not express it. He pretty much acts like a female in that instance. (With reference to genetic disease, not social behaviors or anything like that. They'll be normal men otherwise.) Take a look at the karyotype of an XXY male.