And the reason why is that you get a duplication of the sex chromosomes.

其原因是染会发生复制。

The five A longstanding hypothesis holds the sex chromosomes to blame Male mammals are in the jargon heterogometic.

一个长期的假设认为，染是罪魁祸首。哺乳动物在行话中被称为异配别。

In mammals like humans, females inherit two big sex chromosomes, while  males inherit one big and one small.

在像人类这样的哺乳动物中, 雌传两条大的染, 而传一条大一条小。

Typically a gamete with 23 chromosomes, including one sex chromosome either X or Y, develops when parent germ cells undergo the process of meiosis.

正常的配子包含23条染，其中有一条X或Y染，由亲代生殖细胞减数分裂产生。

So having a small sex chromosome at all may  put a critter at risk for a shorter life.

因此，拥有较小的染可能会使动物面临寿命较短的风险。

So the study showed us for the first time the importance of sex hormones and sex chromosomes working together to influence...

所以这项研究首次向我们展示了激素和染同作用以影响… … 的重要。

And you can see they ended up getting " sex chromosome" -- it's like a pretty juicy title, it popularized genetics, you know?

你可以看到他们最终得到了“染”——这就像一个非常有趣的标题，它普及了传学，你知道吗？

As they go from a cell with 46 chromosomes to a sex cell with only 23, the chromosomes within each pair swap some sections.

当它们从一个有 46 条染的细胞变成一个只有 23 条染的细胞时，每对染中的染会交换一些部分。

While there may be an advantage to having two big sex chromosomes, there's also evidence there's  a disadvantage to having a small chromosome.

虽然拥有两条较大的染可能有优势，但也有证据表明拥有一条较小的染有劣势。

None of those markers was on the x or y sex chromosomes and their total combined effect accounted for less than 1% of the variance.

这些标记都不位于X或Y染上，它们的总联合效应不到变异的1%。

This can happen as a result of nondisjunction of sex chromosomes during meiosis, and it happens more frequently in sperm cells - but egg cells can also be affected.

这可能是由于细胞在减数分裂期间染未分离而造成的，而且这一情况在精子细胞中发生得更频繁，不过在卵细胞中也可能出现。

Every once in a while, when we do that test and we sequence that DNA, there's an extra chromosome 21,13, or 18, or a change in the sex chromosome material.

偶尔在进行该检测时，我们会发现额外的 21 号、13 号或 18 号染，或者染的异常变化。

Sex chromosomes generally come in two sizes,   big and small; part of what determines the sex of an individual is the combination of  sizes they inherit.

染通常有两种尺寸， 大和小；决定个别的部分因素是它们继承的尺寸组合。

One of these pairs, the sex chromosomes, determines person's biological sex and it can be composed of either two X chromosomes for females or an X and a Y chromosome for males.

在23对染中，有一对是染，它决定了人的生物别；对于女，它由两条X染组成，男的则由一条X染和一条Y染组成。

Instead, when you look across the animal  kingdom, the animals that die earlier, regardless of their sex, have something else  in common: they have a small sex chromosome.

相反， 当你纵观动物界时，那些较早死亡的动物， 无论别如何，都有一个同点：它们的染较小。

Like, it can mean having different combinations of sex chromosomes – as in Klinefelter Syndrome, which creates chromosomes XX and Y, or in Triple-X Syndrome, which results in XXX.

比如，这可能意着拥有不同的染组合——就像克兰费尔特综合征，它导致XX和Y染的形成， 或者三X综合征， 结果是XXX染。

Variants in many other genes may also prevent production of either eggs or sperm. Some people even have different combinations of sex chromosomes in different cells of their bodies.

许多其他基因的变异也可能阻止卵子或精子的产生。有些人甚至在身的不同细胞中拥有不同的染组合。

And so what we think happened in this rat is they actually shed that extra xy chromosome or those sex chromosomes and they're able to reproduce as a tetraploid animal.

因此，我们认为在这种老鼠身上发生的情况是，它们实际上失去了那个额外的XY染或那些染，并且能够以四倍动物的身份进行繁殖。

And eventually, someone was like, " Well, if that one thing's called X, should we call this other thing Y? " And like that, (Snaps fingers) the sex chromosomes had been discovered.

最后，有人说，“好吧，如果那个东西叫 X，我们应该把另一个东西叫 Y 吗？ ” 就这样，（打响指）染被发现了。

There are two possible explanations for why  this trend exists: one is that having more big sex chromosomes is better, and the other  is that having a small sex chromosome is worse.

这种趋势存在的原因可能有两种：一是拥有更多的大染更好，另一种是拥有较小的染更糟糕。