Questions tagged [embryology]

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

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4answers
12k views

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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1answer
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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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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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4answers
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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, ...
11
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2answers
636 views

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 ...
11
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2answers
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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 ...
11
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1answer
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Has the gestation (pregnancy) period for humans always been 9 months?

At this point in our evolutionary progress, the expected human gestation period is (roughly) nine months long. My question is, has this duration of time always been the same for homo sapiens? Or, are ...
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2answers
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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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2answers
7k views

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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1answer
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Can only fully matured sperm fertilize an egg?

Are only mature sperm able to fertilize an egg? If so, is there typically a reserve of mature sperm that are saved after an ejaculation or does a male need to wait for new sperm to mature before ...
7
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1answer
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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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1answer
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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 oesophagus....
7
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1answer
943 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 ...
7
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1answer
95 views

How does a cell distinguish left from right?

Although the human body is mostly left-right symmetrical, it consistently has asymetries. The heart is consistently slightly to the left side of the body. The liver is consistently on the right side. ...
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3answers
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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) ...
7
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1answer
668 views

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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2answers
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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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1answer
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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 ...
6
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1answer
92 views

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 ...
6
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1answer
113 views

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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1answer
136 views

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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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 ...
5
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1answer
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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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2answers
254 views

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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1answer
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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 the ...
5
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1answer
122 views

Can 12 mitotic divisions produce 6000 nuclei?

The following quote is from "Principles of Development" by Tickle & Wolpert: "After fertilization and fusion of the sperm and egg nuclei, the zygote nucleus undergoes a series of rapid mitotic ...
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1answer
391 views

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 ...
5
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1answer
820 views

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 ...
5
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1answer
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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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1answer
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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 ...
4
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1answer
8k views

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 ...
4
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1answer
107 views

When does the brain stem appear in humans?

This article states: Once the neural tube closes, at around week 6 or week 7 of pregnancy, it curves and bulges into three sections, commonly known as the forebrain, midbrain and hindbrain. ...
4
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1answer
172 views

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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Are there predefined implantation sites in mammalian uterus?

I do surgical embryo transfer of genetically modified (microinjected) mouse embryos (at 1 or 2 cell stage). As most of the constructs are new, we expect that it may affect birth rate. In case there ...
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0answers
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Why are sutural bones more common in lambdoid suture? [closed]

Why are sutural bones (Wormian bones) are more commonly present at lambdoid suture? Is the tortuous nature of lambdoid suture a reason for that? Evidences for my claim: They(sutural bones) occur ...
3
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1answer
256 views

Does the mesoderm evolve from the ectoderm or the endoderm?

I know the embryos of most animals develop into 3 germ layers. However primitive animals, such as Cnidarians, only have 2 germ layers - they lack a mesoderm. Therefore the 3rd germ layer must have ...
3
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1answer
112 views

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?
3
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1answer
548 views

How can there not be purpose movement in the fetus until week 18, when a fetus can open its mouth and suck its fingers at week 11?

According to Fetal Movement According to an overview produced by the Royal College of Physicians of Edinburgh, purposive movement begins at about 18 weeks, gradually replacing reflex movements ...
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3answers
160 views

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 ...
3
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1answer
225 views

Is a part of the spinal cord from the mesoderm?

The caudalmost part of the neural tube is formed by the caudal eminence. Isn't this mesodermal? So does it mean that, a part of the spinal cord is mesodermal in origin? Does it have any significance ...
3
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1answer
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Mesoderm vs Mesenchyme- what's the difference?

My embryology textbook states that mesoderm can exist as Mesenchyme or Epithelium. I'm not sure what 'epithelium' means. Here is a quote for context: Somatic, splanchnic, and somite mesoderm can be ...
3
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1answer
380 views

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 '...
3
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1answer
986 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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2answers
893 views

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 ...
3
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1answer
635 views

Is the blastocyst a coeloblastula?

A coeloblastula is that type of blastula which has a fluid-filled cavity. Since the blastocyst of mammals has a fluid-filled cavity too, can it be called a coeloblastula? My book however mentions the ...
3
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1answer
332 views

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 ...
3
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1answer
345 views

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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0answers
111 views

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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2answers
106 views

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?