High school biology
Human fertilization and early development
Overview of fertilization and early human development. From conception leading to a zygote to blastocyst, embryo and fetus.
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- Sal said something about it potentially forming a human life, but I know a lot of people especially in certain faiths like mine believe life is made in that moment. Scientifically when is it no longer potential life but actual life? When the egg attaches to the uterus?(8 votes)
- Concerning religious perspectives of when life begins, it's not anyone's job - including mine - to tell someone whether they're right or wrong. It's their choice to take on any faith or belief they choose. So disproving religious views should be left out of any discussion regarding the start of life. That being said, from an objective view, religious views of conception shouldn't be used to promote any assertion of when life begins either. In general, it's safe to say that religious perspectives and any other views with no scientific basis should be left out of the matter as a whole.
From a scientific perspective, it is crucial to remain as impartial as possible. For even in the scientific community, there is much disagreement concerning the answer to when life begins. Some say that conception is the only consistent way to draw line, while others claim that a fetus isn't its own, distinct individual until its umbilical cord has been cut from the mother. There are also people who propose that life begins when the fetus's heartbeat can be detected with a doppler (around 10-12 weeks) and some place the time later in the second or third trimester. I am of the opinion that between conception and birth there lies a gray area where no black or white can be truly established (at least at the moment). Conception, although very well studied, is a very complex and rapid event, occurring in less than a second. With our limited understanding, it is difficult to prove a point in time as the beginning of life between a fetus' earliest possible inception to its exit from the womb.(14 votes)
- If 1 sperm cell fertilizes the egg cell, what happens to the other thousands of sperm cells?(5 votes)
- They most likely die to to lack of ATP being produced.(9 votes)
- When a fertilized egg is dividing. That doesn't seem like the simple Mitosis that was described in the last unit. In the Mitosis videos it seemed like it was describing replication of a single cell.
Is this type of division still Mitosis or is it something else?(4 votes)
- No it is still normal mitosis. Once the sperm cell fuses with the egg cell, it becomes one cell, known as the zygote. This zygote (fertilised cell) then divides just like any other cell going through mitosis.(4 votes)
- What if more than 1 sperm fertilizes an egg cell? Is that how twins were created?(3 votes)
- Nope. One sperm wins the race. Twins are when the resulting fertilized egg divides, or when there was more than one egg present to attract sperm.(4 votes)
- The Kaplan biology textbook state that "the embryo becomes a solid mass of cells known as morula, which undergoes blastulation to form blastocyst"? As compared to this lecture video that states that embryo comes after blastocyst. Which is correct?(3 votes)
- The Kaplan biology textbook is mistaken. It should have said "the fertilized egg becomes a solid mass of cells known as a morula, which undergoes blastulation to form a blastocyst." The fertilized egg rapidly divides. The blastocyst implants in the uterine wall. It is not until the cells begin to differentiate--becoming distinct cell lines such as brain cells or skin cells or liver cells--that the blastocyst becomes an embryo.(2 votes)
- would someone have different genetic materials such as looks, gender, personality, etc if another sperm fertilized the egg ?
For Example :
one of the thousands of sperms that fertilized the egg made you how you are today, suppose instead of that sperm another sperm fertilized the egg, would it still produce you as you are today, would you differ in gender, looks, personality , etc everything ?(2 votes)
- Your question applies to the law of independent assortment. Traits are inherited independently of one another. One sperm cell could have one trait and not another. If another sperm fertilized the egg, you would be different.(2 votes)
- if1 sperm cell fertilizes the egg cell,what happens to the other thousands of the sperm cells(2 votes)
- are the genetic material in every sperm the same?(2 votes)
- What if two sperms fertilization with one egg?(2 votes)
- How do sperms become the shape of the tadpole when meiosis happening?(2 votes)
- [Instructor] What we're gonna do with this video is talk about fertilization and development in human beings or at least early development in human beings. And this right over here is an actual image of fertilization about to happen or happening. So this right over here is a sperm cell. One of the many sperm cells that will come from a male human being, and this right over here is the egg cell that is inside the female human being that it is actually fertilizing. Fertilization is the sperm cell coming together with this egg cell and this act, this is the conception of what has the potential to turn into a real organism, in this case, a human being. So let's just first appreciate the scale here. Just appreciate how small these things are. A distance of about that would be approximately one-fiftieth of a millimeter. So this is happening on a very, very, very small scale. Now another thing that you should be appreciate and something like this occurred at the beginning of every one us, is that this is one of maybe several hundred million sperm cells are in competition to be the one that gets to that egg cell and so you should feel proud of yourself or at least half of yourself. You won a pretty big race, think about it, there's 300 million people in the United States that half of you that was from your father that won a race with the several hundred million of the other sperm cells from you father to get to be that DNA, that combination of DNA from your father that will then fuse with the combination of DNA that's from your mother in this egg cell. And so how is that DNA packaged? Well it's packaged in chromosomes. Chromosomes are just strips of DNA and a full set of human DNA in most of the cells in your body, you have 46 chromosomes and it's really 23 pairs of two. In each pair, you have one from your mom and one from your dad. But it turns out that in these sex cells, and we call these gametes right over here, let me write this down, these are gametes. So a sperm cell is the gamete that comes from your father and an egg cell, or an ovum, is the gamete that comes from your mother. Gametes have half the number of chromosomes. Each of these have 23, not 23 pair, they have 23 chromosomes. And so when the sperm and the egg come together when the egg is fertilized, then all of a sudden, you once again have 46 chromosomes or 23 pair. But what does it look like as soon as fertilization has occurred? Well, this right over here is a picture of a zygote which is this fertilized, you could view it as a fertilized egg, it's now starting to have all 46 chromosomes, and what's interesting here is you can see the nuclei from the two cells, they haven't completely fused yet. These right here, these are called pronuclei but they will eventually fuse and that, when you think about your first day as a cell, that's when the genetic makeup that you got form your father and your mother came together to be the genetic makeup that would eventually give all the information or most of the information necessary to construct you. Now as soon as this happens, you start having cell division so the zygote, this zygote right over here through the process of mitosis, it will then split into two, and then split into four, and you have about a cell division or two everyday or so. And so after about two, three days, you have about eight, then 16 cells, those 16 cells are called morula, and then eventually, that keeps splitting and after about five to nine days, you have something that looks like this and you can't really appreciate it but there's two to three hundred cells here. There's two to three hundred set cells in this sphere and it's actually hollowed out on the inside, you can't fully see it right over here, but this thing is called a blastocyst. And then, and notice it's still roughly on the same scale, it's a little bit bigger than that original egg cell that was fertilized, but then this will continue to split and split and split. And just to appreciate the entire stages that we're talking about, so when we talk about fertilization, we're talking about right over here. So all these pictures that I'm showing you are right in this phase, and then if you go maybe three, four, five, six, seven days maybe in that first week, you get to this blastocyst stage and so we are right over here on our timeline. Now one thing that you might be intrigued by is why am I starting this at week two. Well it turns out that there is also a gestational age and gestational age is something that doctors and scientists will use as a measure of how far long this embryo is and eventually the embryo or the fetus is and gestational age in particular is measured from the first day of the mother's last menstrual cycle which can be two weeks before the actual moment of conception which I am showing right over here. So that's just a little technical thing that is interesting and why you see this roughly two week shift. But then we get into this phase where people would consider it to be an embryo and near the end of the embryo stage, you might have the potential human being to look something like this. This would be about seven weeks after conception and you could see even here, it is quite small. This is about one centimeter in length so about the size of a blueberry. But you hardly see something that's starting to look like a human being or at least a mammal and one of the fascinating things about developmental biology is that if you look at the animal kingdom especially things that are closely related to human beings, you will see even at this stage things look quite similar but you already start to see things that you'd recognize, you can see arms right over here, you can see kind of an early ear, you can see an early eye, nose, even ribs it looks like, and so this is already beginning to resemble a human being but it is quite small and if you look at the development of other mammals or even things that aren't mammals, even things like fish, you see things that look not too different from this at this stage. But then once you get into, you're going into the 10th, 11th, 12th weeks, then people will call this a fetus. So right now, this is an embryo, so this was an egg being fertilized, zygote, zygote goes to morula, goes to blastocyst, you're an embryo, then from an embryo, you go into being a fetus. And so this is an image of a fetus being connected to the placenta and the placenta is really the interface with the mother's body. And you can see even here, it is quite small depending on your screen size, this might be about the same scale on my screen right now this is about five centimeters in actuality, so this is about the size of this fetus. And the boundary between embryo and fetus isn't super well-defined that's why you see this kind of transition point, but most people would consider it to be once you get into about the 12th week, you're definitely a fetus. Now some interesting things right over here as you see the entire cycle all the way until you get to the 36th through the 42nd week which is when most, when what is considered kind of full term when a baby is ready to come out but you start to see over here, this notion of viability which is roughly a time where there's a decent chance that if the baby were to come out of the womb, they would survive on their own and this is just an interesting stat that there's roughly a 50% survival rate at around the sixth month. But the general big idea's here and it really is mind boggling, all of us start in this almost grand race of sperm between hundreds of millions of sperm cells to be the one to fertilize your mother's egg and then that one cell, that zygote that has the genetic information from both your mother and father, now that that egg has been fertilized, it then keeps replicating until it turns into a fairly complex organism that is capable of making videos and reflecting about how it developed.