#prenatal development

[ID: A graphic that shows a realistic picture of a fetus. Underneath it, words read, “Know the facts about fetal pain.]

Fetal pain is real and have a right to access pain relief and proper health care in that regard. Parents also have a right to be fully informed of this reality when considering medical options that may physically harm the fetus.

Gametes

Plants and animals produce special sex cells called gametes. There are two types of gametes:

eggs (larger & immobile)

sperm (smaller & mobile)

Eggs are produced by female organisms, so they're also called female gametes. Sperm is produced by male organisms, so they're also called male gametes.

A human egg surrounded by sperm (magnified 400 times).

Mating is the act of transferring sperm from male to female. A sperm must reach the egg for their genes to be combined.

For most plants, the flowers are the reproduction organs. Flowers usually contain both male and female organs (sperm are found inside pollen).

Pollination is the act of transferring pollen from the male to the female organs of the plant.

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Gametes, Chromosomes and Fertilization

There is a complete set of genes inside each egg or sperm. Each gamete contains around 30,000 genes.

These genes are linked to one another in long strings called chromosomes.

A human gamete usually has 23 chromosomes, so a chromosome consists of thousands of genes.

After mating (or pollination), the sperm swim to the eggs. Fertilization occurs when one sperm fuses with an egg.

Early human zygote observed 18 – 20 hours after insemination. The two pronuclei (male & female) have not yet fused and combined their genetic information.

Fertilized egg of the roundworm Ascaris lumbricoides (multiplied 400 times).

The resulting cell is called a zygote. It's the start of a new organism.

The zygote has twice as many chromosomes as the sperm or egg. It has received 23 chromosomes from each gamete, so now it has 23 pairs (46 chromosomes in total). They're located in the zygote's cell nucleus.

A cell that has the full 23 pairs of chromosomes is diploid (most human cells are diploid). But gametes have only 23 individual chromosomes, so they are haploid.

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Growth and Development

The zygote divides into two cells via the process of mitosis. Now there are two cells, each with a complete identical copy of the original zygote's chromosomes.

The new organism continues to grow, as the process of mitosis continues. Eventually it becomes an embryo, consisting of thousands of cells.

An embryo at the end of 7 weeks of development (derived from an ectopic pregnancy). It is 10mm in length.

Different cells become specialized into different tissues (e.g. skin, nerves & muscle). These form organs (e.g. arms & legs).

This process is called growth and development.

Growth & development continues until a complex organism is formed, made of millions of cells.

Each body cell has a set of chromosomes that are identical to those of the original zygote (due to the process of mitosis).

The zygote inherited a complete haploid set of genes from each parent Therefore, the growing organism has two genes for each trait (one from each parent).

The two genes for a particular trait may be identical (e.g. two genes for blue eyes). Or the two genes may code for different forms of that trait (e.g. one gene for blue eyes, and the other for brown eyes).

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Mitosis

Mitosis is a process whereby a single cell divides once into two identical daughter cells (via cell division). The main purposes of mitosis are growth and replacing worn-out cells.

First, the DNA in the cell is copied in preparation for cell division. This results in two identical sets of chromosomes.

The membrane around the cell nucleus dissolves away, releasing the chromosomes.

A membrane forms around each set of chromosomes, creating two new nuclei.

The single cell pinches in the middle, forming two separate daughter cells. Each has a full set of chromosomes within a nucleus.

Diagram of mitosis.

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Sex and Variation

A mature organism produces gametes from body cells via the process of meiosis. Female animals produce eggs in their ovaries, and male organisms produce sperm in their testicles.

The chromosomes are sorted so that each gamete gets half the number of chromosomes found in body cells, and so that each gamete ends up with a different set of chromosomes.

When a sperm & egg collide at fertilization, the new organism inherits a unique collection of chromosomes.

This process of allocating chromosomes at meiosis, and creating new combinations at fertilization, is what produces the variation seen among siblings.

It also helps to generate variation within plant & animal species.  This is important for survival when the environment changes.

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Meiosis

Gametes are formed via the process of meiosis. This is a process whereby a single cell divides twice to produce four cells, each with only 23 individual chromosomes (instead of 23 pairs of chromosomes).

First Part of Meoisis:

The DNA in the cell is duplicated, which results in two full sets of chromosomes. The pair of chromosomes may then exchange bits of DNA, in a process called recombination (or crossing over).

The membrane around the cell nucleus dissolves away, releasing the chromosomes.

The chromosomes are pulled apart, so that at each pole of the cell, a full set of chromosomes gathers together. A membrane forms around each set of chromosomes to create two new nuclei.

The single cell then pinches in the middle to form two separate daughter cells, each with a full set of chromosomes within a nucleus.

Second Part of Meiosis:

Now you have two daughter cells, each with 23 pairs of chromosomes. The second part of meiosis happens the same way to both daughter cells, at the same time.

A pair of chromosomes is made up of two chromatids, which are joined at the centromere.

As before, the membrane around the cell nucleus dissolves away to release the chromosomes. But now the pairs split apart, so that each chromatid of a pair moves to opposite ends of the cell. Now you have 23 individual chromosomes (or chromatids) at each pole of the cell.

A membrane forms around each set of 23 chromosomes to create two new cell nuclei. The cell pinches in half to form two new “grand-daughter” cells, each with only 23 individual chromosomes.

At the end of the process, there are four gametes, produced from one single parent cell.

Diagram of meiosis.

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Twins

Identical twins are formed from a single egg and a single sperm. They combine to form a zygote, and the zygote divides into two cells as usual (each with the same set of chromosomes). But these two cells then separate, and each grows into an independent organism.

Each organism has identical genes, so they grow up to be identical twins.

Non-identical twins are formed from two eggs, each of which is fertilized by a single sperm. So non-identical twins are no more alike than regular siblings.

Abdominal ultrasonography of twins at gestational age of 15 weeks.

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the use of the term “fetus” by pro-choice people when discussing abortions. 

abortions only rarely involve fetuses. when abortions are safe, legal, affordable, locally available, have short or no wait times, and are all-around easy to access, it’s even more rare. 

abortions usually involve zygotes or embryos. 

A few people have asked us about the TikTok of a young woman arguing that the "biological narrative" of pregnancy conceptualizes the fetus as a parasite.

Dr. Calum Miller recently addressed the video on Twitter, and we are reposting his response here:

This viral video about fetuses being parasites is honestly the perfect example of what happens when you give a first year undergrad a small bit of technical knowledge and a camera. (I'm not saying she is a first year undergrad - just that she comes across like one.)

1) She seems to think there is an interesting difference between the ‘body knowing its pregnant’ and the fetus ‘tricking’ the body into knowing that its there through hCG. Obviously the only way the body could know that it is pregnant is by some sort of signal from the fetus. To try and distinguish these is unintelligible. This is like saying that your body doesn’t know that it is cold: the cold forces your body to warm up. They are one and the same thing.

2) She seems to suggest that the outer layer of the zygote/embryo preventing an immune response is a 'trick'. But the immune system helps to clear the debris from any cell rupturing, including the mother's cells. That doesn't show the cell is an 'invader'.

3) She seems to think it is interesting that parasites and fetuses occasionally use some similar mechanisms for evading an immune response. That is how evolution works. There are occasional similarities between how parasites and the mother's cells evade immune responses too - but this is clearly irrelevant.

4) The final point about suppressor cells seems to undermine her argument. Suppressor cells do the same job for the mother's cells, preventing them from being attacked – but we wouldn’t call it a ‘trick’ as if her cells are actually invaders.

5) She seems to think it is significant that the fetus makes the placenta and puts it into your body without you knowing. 99% of things in our body are done without us knowing, so this is obviously not significant in any way.

6) How does she think a baby could ever exist without, in her words, ‘tricking’ the mother? It has different genes because it is a different human being – obviously it has to avoid immune attacks (just as all cells within the mother do). To say that this is a ‘trick’ is just assuming from the outset that the baby doesn’t belong there. You could just as easily (in fact more so) interpret it as the clever mechanism nature has come up with to defend both a mother and her baby from autoimmunity. Calling it a trick is really just assuming the conclusion – that the fetus doesn’t belong there. But the falsehood of the conclusion is actually more obvious than its truth – obviously the fetus belongs there: that is how reproduction works and that is why any animals exist at all.

7) You could obviously portray the entire immune system as a kind of ‘trick’ if you really wanted: the whole immune system has developed mechanisms to make sure it only targets foreign things and not host cells. This isn’t a ‘trick’ in the sense that the host cells are actually foreign invaders; it’s just how the immune system had to evolve: it had to recognise host cells (and offspring), and attack other things. Obviously this doesn’t always work. To try and extract a narrative out of this is frankly completely bizarre.

8) Most of this seems to just boil down to the profoundly uninventive claim that babies are genetically distinct from their mothers and hence need biological mechanisms to evade the immune system. Well, obviously. But mum's cells need some of those tricks as well!

9) This all just depends on the claim that the fetus is invading. But obviously this isn’t plausible – the fetus is there in its natural habitat (as we all once were) with no culpability and usually as a result of an action the mother took which she knew would result in that. It is like saying the person in the apartment above you invaded your apartment because you smashed your ceiling/their floor in. It's basically just putting a moral spin onto some rudimentary biological facts and it is embarrassing.

10) While we're here, did you know that, far from the baby typically harming her mother, mortality rates after abortion are way, way higher than after childbirth? https://calumsblog.com/2022/02/10/abortion-and-maternal-mortality/ for more info.

And did you know that the baby produces stem cells which go round mum's body healing her tissues, e.g. from heart attacks, strokes, liver damage, and more? One leading scholar concludes: "after the mother spends 9 months providing nutrients and an environment for optimal growth and development of the baby, the baby gives back cells with regenerative potential to the mother...it is the mother who benefits". [Fetal Cell Microchimerism in the Maternal Heart: Baby Gives Back, Stephanie Pritchard and Diana W. Bianchi]

Pregnancy is normal. It is healthy. It is beautiful. Let's stop dehumanising women and children by pathologising it.

Recently there has been a trend in the abortion advocacy community of using medical terminology to draw arbitrary lines regarding when an embryo or fetus’s humanity begins. To some extent the pro-life community also plays into this trend, particularly with laws designed to limit abortion access based on milestones in fetal development (awareness, purposeful movement, nerve development, heartbeat). Every line the pro-life community draws is then countered by pro-choice arguments that those lines don’t truly matter. So as heartbeat bills become a more popular tactic, we see increasing resistance from abortion advocates and the press to the idea that fetal cardiac activity represents something meaningful. Despite using scientific-sounding terms, this resistance often relies on arguments that are scientifically inaccurate or misleading.