The study of the development of an embryo from fertilisation through to description as a foetus.

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Why is polyploidy lethal for some organisms while for others is not?

Polyploidy is the multiplication of number of chromosomal sets from 2n to 3n (triploidy), 4n (tetraploidy) and so on. It is quite common in plants, for example many crops like wheat or Brassica forms. ...
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Impact of Alan Turing's approach to morphogenesis

Shortly before his untimely passing, the computing pioneer Alan Turing published his most cited paper The Chemical Basis of Morphogenesis (1952). The central question for Turing was: how does a ...
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Could a fetus properly develop in micro/zero-gravity?

I suppose another way of looking at the question is: how important is gravity for the development of mammal fetuses? And if things would go wrong, what sort of things would they be, and what would be ...
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Why do pandas have a high probability of giving birth to twins?

According to the BBC documentary "Wild About Pandas", about half of panda birth result in twins. Why do they have such a high probability compared to other mammals? What factor(s) control that ...
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Do twins “run in the family”?

My wife and I recently found out that we are going to have twins and so nearly everyone asks if we have a family history of twins. Now I know that the answer for me is that it doesn't matter—as ...
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What determines testosterone exposure in womb, baby's genetics or mom's body?

I read this article which has the following quote: The ratio between index and ring finger is believed to be linked to exposure to the male hormone testosterone in the womb. And I wonder what ...
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How does an embryo know where to grow limbs etc

For example you have a cell or already a bunch of cells. Those cell(s) divide and after several week you have a grown organism, for example a human with limbs, several different organs etc. However, ...
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How are babies born without a brain?

In the United States, anencephaly occurs in about 1 out of every 10,000 births. There are several forms of this condition, wherein the forebrain is absent. The forebrain is host to most of the higher ...
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Does our eyeball increase in size as we grow?

Does the size of the eye increase as we develop from the stage the complete eye first forms to infancy and then to adulthood ?
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Do birds have navels?

This picture shows the development inside a bird egg: This shows the connection of the embryo to the yolk sac. Does this mean birds have navels? And if so, what happens to the umbilical cord once ...
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641 views

evolutionary reason behind sharing the same path for food and air?

What is the evolutionary reason behind sharing the same path for food and air? For example, we have a nose and lungs, yet they are linked by the pharynx, which is shared with the mouth and ...
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610 views

Why are eggs “egg” shaped?

Is there a reason as to why chickens lay "egg" shaped eggs, as opposed to spherically shaped eggs (or a random shape)? <--- Main Question For extra points (actually just to add more words in ...
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Cytoplasmic determinants - protostomes and deuterostomes

Cytoplasmic determinants are spread unevenly in the egg, and so when embryo starts forming (cells start dividing), the determinants are also unequally divided between cell. This unequal distribution ...
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What metabolic activities are performed by a developing human fetus's liver?

I understand that organ function varies with the stages of development. Does a fetal liver EVER perform lipogenesis, gluconeogenesis, make bile, etc? Or does it only begin performing these actions ...
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832 views

What forms the human amniotic sac?

I am trying to understand the formation of embryonic disc for human and chick so the following question is related to here about formation of embryonic disc. I had thought that the amniotic sac forms ...
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Is telomere shortening consistant over consecutive cell divisions from zygote to a differentiated cell?

Considering the complexity of embryogenesis, a temporal referance would be helpful to coordinate the developmental sequences during embryogenesis and fetal development which is to be completed within ...
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How compatible are mammal wombs?

I had read about science working towards the creation of artificial wombs however I wonder how compatible are mammal wombs and connected systems to develop fetuses. What species are so compatible that ...
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What is the total number of rounds of cleavage during mammalian embryonic development?

That for frog is 12, but what about mammalian embryos? I cannot find the exact number anywhere.
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There are linear and rotary molecular motors in the cells. Do any of them have a fixed or stable frequency or speed?

Are there any linear, rotary or oscillatory molecular motors in the cells which can have fixed frequeny and which can be used as a reference for elapsed time timer? This question is with relevence to ...
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When does Coelom form exactly?

Related to my other question. I know that the coelom is derived from mesoderm. Coelom seems to form during organogenesis within 3rd and 8th week of embryogenesis. However, that answer is not either ...
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Fetal development, gastrulation and embryonic disc

I am completely confused by the images circulating on the internet of human gastrulation. First, lets see how it happens in deuterostomes. This image depicts the process: (image is from Wikipedia) ...
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Do humans have Coelom?

Kimball Biology 5e says Coelom is the main body cavity of many animals. It is lined with an epithelium derived from mesoderm. Gilbert Embryonal Biology 9e says Coelom is the space between ...
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128 views

Unknown animal - What could it be?

It's the first time I use this website and I really need help because I'm totally stuck Now I'm in school, but I'm trying to prepare for the Olympics During the preparation, I found the issue on the ...
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1answer
174 views

How late in a human pregnancy can a zygote split?

This page indicates that the first two days is "very early" for a zygote to split, and that conjoined twins are the result of an "extremely late" split: If the zygote splits very early (in the ...
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Causes of monozygotic twins

Twins could be monzygotic i.e. identical twins and dizygotic i.e. non-identical twins.Well, monozygotic twins occur when a single egg is fertilized to form a zygote which later divide into separate ...
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which exact mechanism triggers the first cell differentiation after n divisions?

I would like to understand which mechanism triggers the first cell differentiation after n divisions. I read previous articles on SE and Wikipedia articles on cellular differentiation and ...
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What are differences between formation of embryonic disc in chick and mammal embryo?

Exam question which got lowest average points in my university: 1/5 average. No markscheme available so my attempt below. I assume that embryonic disk prefers to germ disk such that Formation prefers ...
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How only one follicle develops into graffian follicle?

I've studied that one out of many follicle develops into mature or graffian follicle. The fact which confuses me is that, since all follicles are in same ovary, close to each other with equal supply ...
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If two definitive ovums are fused will they form an organism?

Pretend that somehow in a laboratory two definitive ovums (finished 2nd miotic divisions) are are fused together. Will they form a new species?
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Is the thecal sac ectoderm?

The thecal sac, or dural sac, is the membranous sheath of dura mater that surrounds the spinal cord and the cauda equina. The thecal sac contains the cerebrospinal fluid in which the spinal cord ...
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How long do zebra fishes remain transparent?

As larva, zebra fishes are transparent, at least up to 5-6 days. I wonder what would be the upper limit of the transparent period. This is of relevance considering purposes for imaging. The question ...
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392 views

Development of vitreous humor

I have tried reading about development of vitreous humor but it is all very confusing. When does it first developed ? Does it renew itself ? Please provide reliable sources..
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Does chicken embryo form the disc called “discoblast” in the cleavage and blastulation of chicken?

This thread is related to my previous thread which is still unsolved mainly. I need to be able to compare chick and human cleavage and blastulation of zygote. My friend says that Chicken have ...
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Activation Of Embryonic Genome

Embryonic gene activation is a process by which the embryo begins to transcribe its newly formed genome.As the embryonic gene activation occurs during early stages the paternal genome may not have any ...
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Where does meiosis II of oogenesis end exactly in tuba uterina - uterus?

I know that metaphase II ends at ampulla tuba uterina, but I am not completely sure where the telophase II ends. Is it in the triangular section of cervix uterii? I just have an intuition that the ...
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Is there a realtime molecular clock within the genome to co-ordinate the developmental sequences in an embryo?

It is difficult to assume that the massive number of co-ordinated developmental sequences in a developing embryo is controlled by molecular signalling alone. Is anyone aware of a molecular or ...
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114 views

Which process is needed to complete male reproductive development?

In order to properly complete male reproductive development: ...
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38 views

How many areas are there in Brodmann map?

I read Wikipedia claiming 52. I heard that this can be extended to 54. I see there is no limit of having more areas - just better understanding of the neuroblast migration and fibroblast too, ...
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Simulating Cell differentiation

I'm a computer programmer deeply interested in Biology. I wish to write a computer simulation for cell differentiation. I understand there will be seemingly impossible challenges in doing this. But ...
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37 views

What is the mechanism of folic acid deficiency and neural tube defects?

I am having difficulty finding the mechanism by which folic acid reduces the risk of neural tube defects. I know that it does so, but what in particular actually occurs with folic acid deficiency to ...
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1answer
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Roles of creatine and bilirubin in foetus circulation

I think they are not inputs from maternal placenta. I think they are the results of foetus metabolism. However, I do not understand it how and where exactly. What are the roles of creatine and ...
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912 views

How many consecutive cell divisions are required to form the adult human body from the single cell zygote?

The preferred question would have been what is the total number of cells in a full term human foetus and how many cell divisions are required to reach that number. However estimates of total cell ...
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184 views

Why are Birds and Reptiles with abundant yolk sac polyspermic?

I was given an explanation that birds and reptiles are polyspermic because they have an abundant yolk sac. But how does it explain the thing? Chicken as an adult is not using in my opinion yolk as an ...
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Front versus back in animal anatomy [closed]

Throughout various species, there seems to be a clear distinction between the front and the back. The musculature of the front, when engaged, closes or curls up the body, protecting it, while the ...
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Is the blastocyst a coeloblastula?

A coeloblastula is that type of blastula which has a fluid filled cavity. Since the blastocyst of the mammals does too, can it be called a coeloblastula? My book however mentions the two as different, ...
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Which part of the genome are the developmental sequences of embryogenesis located?

Which part or parts of the the genome are the sequences located. Are they spread across the chromosomes? If so how are they accessed sequentially with precision during embrygenesis?
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Which X-Y chromosomes have the developmental genes for mammals?

I know that for a given mammal, half the chromosomes come from father and half from mother. This is typically denoted as x-y. I've recently read about "toolkit" genes that control how a cell develops ...
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Does a zygote express all genes?

If a zygote has all the cytoplasmic determinants and all the specific transcription factors, does that mean that all genes in the genome are expressed?
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What's the difference between an embryo and a fetus?

The most I've been able to come up with is that fetuses are embryos slightly farther along in their development. Is that correct? Thanks! evamvid
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What is the difference between the neural tube and the dorsal ventral cord?

I was wondering what the difference is between the neural tube and the dorsal ventral cord. I know that the neural tube forms during embryonic development from the ectoderm layer that folds inwards. ...