Patterns and processes of sex chromosome evolution

从雄孔雀壮观的尾巴到雄蜘蛛令人眼花缭乱的求偶舞蹈，动物王国里的雄性和雌性在外表和行为上常常大不相同。然而，两性拥有几乎相同的一组基因，那么这些显著的性别差异是如何产生的呢？答案被认为与性染色体有关，因为它们是基因组中唯一一个在女性和男性之间存在差异的区域。在人类中，男性有一条X染色体和一条Y染色体，而女性有两条X染色体，Y染色体是男子气概的本质。然而，其他动物可能有不同类型的性染色体。例如，鸟类有Z和W性染色体。男性有两条Z染色体，女性有一条Z染色体和一条W染色体。此外，所有哺乳动物都是XY型，所有鸟类都是ZW型，而壁虎是少数在不同物种中同时拥有XY和ZW性染色体的动物群体之一。我的研究旨在描述鸟类和壁虎性染色体的多样性，并探索它们在雄性和雌性之间产生生物学差异方面的作用。就像Y染色体对哺乳动物的雄性很重要一样，W染色体对理解雌性特征也特别有趣，比如鸟类的产卵。然而，这两种有性别限制的染色体的生存都受到威胁。染色体消除错误突变的方法是在繁殖过程中配对和交换基因。单个的W和Y染色体没有这种选择，因为它们没有伴侣可以配对，因此不能修复基因错误。随着时间的推移，这些染色体已经腐烂，失去了90%的原始基因含量，现在大部分是基因荒地。但是Y染色体和W染色体的退化是终止的吗？这是否意味着人类和男性的Y染色体最终会灭绝？回答这个问题的关键在于存活下来的基因：它们被保存下来是因为它们的功能如此重要，还是它们的存活是随机的结果？我的研究将通过研究鸟类性染色体来探索基因是如何抵抗这些强大的降解力的，这对退化过程提供了无与伦比的见解。这是因为所有的鸟类最初都有一个相同的W染色体，但数百万年来，曾经相同的W染色体在不同的鸟类中独立地衰变了。这种进化的重复使得测试相同的一组基因是否在鸟类的W染色体上存活下来，并确定它们在雌性特征中的作用成为可能。然而，为了理解性别差异是如何在基因组中编码的，仅仅研究性别有限的Y和W染色体是不够的。对Z和X染色体的研究也有助于解释男性和女性之间的显著差异是如何进化的。在鸟类和一些壁虎物种中，雄性有两个Z染色体副本，而雌性只有一个。因此，Z被认为是雄性艳丽的羽毛和精心制作的求偶歌曲的编码。同样，由于X染色体在女性中比在男性中更常见，因此它被认为在决定女性功能方面起着重要作用。由于壁虎同时拥有XY和ZW性染色体，它们为探索X和Z染色体在决定性别差异中所起的作用提供了极好的机会。因此，我将研究壁虎之间的这种自然变异，并询问X染色体和Z染色体所起的作用如何彼此不同。总之，我的研究将阐明动物界性别决定的巨大多样性。更重要的是，通过研究不同类型的性染色体在多种动物中所起的作用，我的研究有能力极大地促进我们对动物王国中产生令人眼花缭乱的性别多样性的进化机制的理解。

From the spectacular tail of the male peacock to the dazzling courtship dance of male spiders, males and females across the animal kingdom often look and behave very differently. However, the two sexes share an almost identical set of genes, so how do these remarkable sex differences arise? The answer is thought to lie with the sex chromosomes, as they are the only region of the genome to differ between females and males. In humans, where males posses one X and one Y chromosome but females have two X chromosomes, the Y chromosome is the essence of masculinity. However, other animals can have different types of sex chromosomes. For instance, birds have Z and W sex chromosomes. Males have two Z chromosomes and females have one Z and one W chromosome. Furthermore, whereas all mammals are XY and all birds are ZW, geckos are one of the few animal groups that possess both XY and ZW sex chromosomes in different species. My research aims to characterise this diversity of sex chromosomes in birds and geckos and explore their role in generating biological differences between males and females.Just as the Y chromosome is important for maleness in mammals, the W chromosome is particularly interesting for understanding female traits, such as egg laying in birds. However, the survival of both of these gender-limited chromosomes is under threat. The way for chromosomes to eliminate faulty mutations is by pairing up and swapping genes during reproduction. The single W and Y chromosomes do not have this option because they have no partner to pair with, and so cannot repair genetic mistakes. Over time, these chromosomes have decayed, losing 90% of their original gene content, and are now largely genetic wastelands. But is this degeneration of the Y and W chromosomes terminal? Does this mean the Y chromosome in humans and ultimately males will become extinct?The key to answering this question lies in the genes that have survived: have they been preserved because their function is so critical or is their survival the result of random chance? My research will explore exactly how genes resist these strong degradative forces by studying bird sex chromosomes, which offer unparalleled insight into the process of degeneration. This is because all birds originally shared an identical W chromosome, but over millions of years the once-identical W chromosome has decayed independently in different bird species. This evolutionary repetition makes it possible to test whether the same sets of genes have survived on the W chromosome across birds and to identify their role in female traits.However, in order to understand how sex differences are encoded in the genome it is not enough to study only the gender-limited Y and W chromosomes. Studies of the Z and X chromosomes can also help explain how striking differences between males and females evolve. In birds and some gecko species, males have two copies of the Z chromosome whereas females possess only one. Therefore, the Z is thought to encode flashy plumage and elaborate courtship songs in males. Similarly, as the X chromosome is present more often in females than males, it is thought to play a major role in determining female functions. As geckos possess both XY and ZW sex chromosomes they provide an excellent opportunity to explore the roles played by both the X and Z chromosomes in determining sexual differences. I will therefore study this natural variation across geckos and ask how the roles played by the X and Z chromosomes differ from each other. Together, my research will shed much needed light on the huge diversity by which sex is determined across the animal kingdom. More importantly, by studying the role played by different types of sex chromosomes in multiple animals, my research has the power to greatly advance our understanding of the evolutionary mechanisms responsible for producing the dazzling array of sexual variety exhibited in the animal kingdom.