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The Mystery of Ancient Biology: How Is Gender Determined?
Sex-determining systems have long been a fascinating topic in biology, especially when we talk about the differences between different organisms. Ancient texts and modern scientific research have given us a deeper understanding of the formation of gender.
XY Gender Determination System
The XY sex determination system is found primarily in many mammals, including humans and some insects. According to this system, sex is usually determined by a pair of sex chromosomes. In the vast majority of cases, females have two identical sex chromosomes (XX), while males have one X and one Y chromosome (XY).
In this system, the presence of the Y chromosome is key to triggering male development. If the Y chromosome is missing, the fetus will develop along a female path, as seen in Swyer syndrome and de la Chapelle syndrome, which are common in humans.
Mechanism of sex determination
All animals have locations in their DNA that encode genes, with the X and Y chromosomes being specialized in sex determination in many species. In most mammals, sex is determined by one or more genes on the Y chromosome. In this process, the combination of the X chromosome and the Y chromosome determines the sex of the offspring, usually due to some genes on the Y chromosome that are responsible for maleness.
For example, an offspring with two X chromosomes (XX) will develop female characteristics, while an offspring with one X and one Y chromosome (XY) will develop male traits.
Objects and evolution
The XY sex systems of humans and other mammals are structurally similar, especially in the genes that determine sex. As early as the 1930s, research by Alfred Jost demonstrated that the presence of testosterone is required for male development. Later it was discovered that the SRY gene on the Y chromosome plays a key role in promoting the embryo to enter the male development path.
Sex determination in plants
In the plant kingdom, although the XY sex determination system exists relatively rarely, there are many important crops such as kiwifruit and grapes that have this system. Research shows that the XY sex determination system has evolved independently as many as 175 times across different plant species.
Other gender determination systems
In addition to the most well-known XY system, there are various other sex determination systems in the animal kingdom. The ZW system is one of them. In many birds and insects, females are heterozygotes (ZW), while males are zygotes of the same sex (ZZ). In addition, there are some insects that use a haploid system, with males having only one copy of the chromosome (X) and females having two copies (XX).
Influencing factors of sex determination
In addition to research at the genetic level, environmental factors also play an important role in sex determination. For example, maternal hormone levels can affect the sex ratio of offspring. Recent research shows that the transparent layer on the egg's surface not only acts as a barrier to sperm, but may also influence which sperm are more likely to enter the egg.
Human eggs may produce a chemical that attracts certain sperm, suggesting that the process of sex determination is more complex than we thought.
Historical perspectives and future prospects
Early concepts, such as Aristotle's belief that male sperm temperature affects embryo sex, and modern discoveries can even be traced back to the early 20th century. As science advances, the factors that determine sex are gradually explored, including the discovery of the SRY gene, which advances our understanding of sex development.
The study of sex determination not only covers the influence of genes, but also extends to the interactive influence of environmental factors, which allows us to think more deeply about the complexity of life. As science advances, we will gain a deeper understanding of this biological mystery in the future and further explore how gender is determined in different organisms.
