#gamete

STRA8 to Go

Cell division drives the constant flow of life. This replication can take two forms: mitosis, when cells duplicate to two identical copies, and meiosis, the link between generations – the germ line – that produces sperm or egg cells. Studying how meiosis gets going is difficult because it’s hard to collect enough cells just as they begin. But a new chemical trick that prompts many cells to start at once produced a large enough sample for researchers to see what was going on. STRA8 (highlighted in magenta in the mouse testis pictured) is a protein produced by germ line cells (green), but its exact role in meiosis was a mystery. A closer look revealed that it sparks meiosis into action by binding to thousands of different genes, and kicking them into gear. Discovering molecular mechanisms of fundamental life processes, like this wide-reaching green light, is the first step in deducing what goes wrong during disease.

Written by Anthony Lewis

Image by Mina Kojima, Whitehead Institute

Whitehead Institute for Biomedical Research, Cambridge, MA, USA

Image copyright held by the original authors

Research published in eLife, February 2019

Chromosomes Are Not Sexes - Paradox Institute

Some claim that rare chromosome combinations prove there are more than two sexes, yet these combinations still result in males and females, not new sexes.

“Chromosomes are the input, and sexes are the result.”

If you think there’s more than two sexes, you’re a creationist.

By: Heather Heying

Published: Oct 5, 2022

There is an eight-year-old girl who likes to play in streams and look under rocks for squirmy critters. She not only knows how to throw a ball but enjoys doing it. She loves math and logic, and has no interest in dolls or dresses. She will grow up to be a woman. Because that’s what girls do.

There is another eight-year-old girl who likes to give tea parties for her stuffed animals. She likes to dance all the dances, often with other girls who like to do the same thing. She loves to read, and has no interest in trucks or trails. She will also grow up to be a woman. Because, again, that’s what girls do.

One of these girls may want to be an astronaut. The other, a chef. Or a mother. Or a lawyer. An actress. A racecar driver. Are all of these desires equally likely among girls? They are not. Girls are likely to want some things more than others. But guess what: the girls who aren’t girly are still girls. You can tell, in part, by the fact that they grow up to be women. Because that’s what girls do.

Sex isn’t assigned at birth. Sex is observed at birth.

Sometimes, in fact, sex is observed before birth. Most commonly, this happens via ultrasound imaging of the fetus. Less commonly, it is possible to look at the karyotype—a visual representation of fetal chromosomes, organized roughly by size—which has been obtained through the usefully diagnostic but somewhat risky mid-pregnancy procedure known as amniocentesis.

All mammals have “Genetic Sex Determination,” which means that we have chromosomes dedicated to starting us down the path of maleness or femaleness. They are called sex chromosomes, in contrast to the autosomes which comprise most of our genetic makeup, and which do not vary predictably by sex. A tiny number of mammals—the echidnas, and the duck-billed platypus—have several pairs of sex chromosomes. The remaining several thousand of us mammals, however—everything from bats to koalas, kangaroos to whales—all the many thousands of other species of mammals have just one pair of sex chromosomes in each of our cells. Humans are mammals, so we have Genetic Sex Determination. Humans are neither echidnas nor duck-billed platypi, so we have just the one pair of sex chromosomes.

The number of chromosomes in each of our cells varies between species. Ocelots and margays have 18 pairs of chromosomes, for instance, while most other cats have 19 pairs[1]. Most of the great apes, including chimps, have 24 pairs of chromosomes, but humans have only 23. That is: humans have 22 pairs of autosomes, and at that 23rd position: one pair of sex chromosomes.

Humans have 23 pairs of chromosomes in almost all of our cells. Gametes—sex cells—are a notable exception to this[2], however, having only 23 chromosomes each, instead of 23 pairs. If you’re female, your gametes are called eggs; if you’re male, they’re called sperm. If successful (as the vast majority are not), an egg or a sperm will combine with a gamete of the other type and make a new life. As such, so as not to create a new life with double the chromosomes of their parents, gametes have half the chromosomal complement of somatic (body) cells: one copy of chromosome 1, one copy of chromosome 2, etc., all the way down to chromosome 23.

At chromosome 23, females have two nearly identical looking chromosomes, which we call XX. Males, in contrast, have two chromosomes at that 23rd position which are wildly different in size; this we call XY, the diminutive chromosome being the Y.

The gametes of female mammals, therefore—the eggs—all have Xs at that 23rd position. No matter what, a female mammal contributes one of her Xs to her offspring’s genetic make-up.

By comparison, the gametes of male mammals—the sperm—are variable at that 23rd position. For any given male, roughly half of his sperm will contain an X, which, if combined with an egg, will produce a daughter (XX). The other half of his sperm will contain a Y which, if combined with an egg, will produce a son (XY)[3].

The determination of what sex a baby is is usually based on an easy observation at birth, but this isn’t always the case. Intersex people exist, as do people with yet more subtle ambiguities in their phenotypes. The conclusion being imposed on us, far less by trans people than by Trans Rights Activists (TRAs), is that any exceptions to normal function, any fuzziness at categorical borders, proves that we’ve got it all wrong, and that reality is a social construct. It’s not, though. While laws are indeed social constructs, and lawmakers can clearly be captured by ideology, ideological capture does not change the underlying reality. Sex is observed at birth, by looking at primary sex characteristics, or sex can be observed before birth, by looking at primary sex characteristics in utero, or by looking at a karyotype.

All of that is less fundamental than this, however:

Females are individuals who do or did or will or would, but for developmental or genetic anomalies, produce eggs. Eggs are large, sessile gametes. Gametes are sex cells. In plants and animals, and most other sexually reproducing organisms, there are two sexes: female and male. Like “adult,” the term female applies across many species. Female is used to distinguish such people from males, who produce small, mobile gametes (e.g. sperm, pollen)[4].

A woman is an adult human female. Girls become women. Girls do not become boys or men any more than they become fairy princesses or dinosaurs. Fantasize all you want—that is the stuff of childhood, and childhood is the stuff of humanity. But do not confuse fantasy with reality, else you may make decisions based on fantasy that will haunt you for the rest of your life. And do not expect the adults who are paying attention to pretend that your fantasy is real life.

Many adults have either abdicated their responsibility, or are actively in on the game, the game being: hurt the children. Those of us who can see this for what it is, though, who know that providing puberty blockers and sex hormones to children and teenagers is dangerous and immoral, and cutting off their healthy tissue is even farther beyond the pale—we need to speak. We need to put aside what differences we may have.

In some circles, we are all painted with a MAGA brush. It’s a quick route to discrediting a person or position, at least among those who are unthinkingly on the trans train. And yet there are many among us, myself included, who are lifelong liberals[5]. Not only aren’t all of us who recognize that biology is real “MAGA Republicans,” we’re not even all Republicans. Imagine that. Some of us are, and some of us aren’t. And yet we’re all human.

We may not agree on reproductive rights, or climate change, or the second amendment—although I often find that the divide between us isn’t as vast as we’ve been led to believe. But disagreement is fine. It’s good, even. We don’t want to be a clone army, all in lockstep, all believing exactly the same things, living exactly the same lives. We see reality—girls become women, and boys become men—and we are adamant that reality not be hidden from view. And when we find that we actually share core values—values like protect the children from harm—we stand together.

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1 Hsu et al 1963. Karyological studies of nine species of Felidae. The American Naturalist, 97(895): 225-234.

2 Red blood cells are another exception. Humans, like all mammals, have red blood cells which at maturity do not contain nuclei. Red blood cells thus contain no chromosomes (except for what is in the mitochondria. Yes, this is biology, and there is complexity at every turn.)

3 Birds, by the way, do this the other way around. Birds, like mammals, have Genetic Sex Determination (GSD), but unlike mammals, female birds are the heterogametic sex, male birds the homogametic sex. To keep things clear to biologists (but no doubt creating greater confusion among non-biologists), scientists have named the sex chromosomes in birds “W” and “Z” rather than “X” and “Y.” Female mammals are XX, and so are homogametic (homo = same, gametic = marriage (from the Greek)); male mammals are XY, and so are heterogametic (hetero = different). Male birds are ZZ (therefore, homogametic), whereas female birds are WZ (therefore, heterogametic). Thus, it’s mama birds, like papa mammals, whose gametes determine the sex of their offspring.

4 From “I Am a Woman,” which I posted here on March 29, 2022.