My wife and I have argued this, and I've had trouble finding the answer. Which sex carries the genes to determine the sex of the offspring The sex of a human baby is determined by the composition of its sex chromosomes a single distinct pair among humans' 23 pairs of chromosomes. Females possess two copies of the same chromosome referred to as the 'X' chromosome ; males have one copy of the X chromosome and one copy of the smaller, hook-shaped Y chromosome. When fertilization occurs, the new gamete the initial cell from which a fetus grows always inherits one of the mother's X chromosomes, and either a X or a Y from the father, depending on which chromosome the fertilizing sperm cell happened to inherit. One could say, then, that the father-or, at least, his sperm-determines the sex of the child. On the other hand, the first sperm to reach the egg isn't necessarily the one that fertilizes it; human eggs are rather choosy about that sort of thing. So, in an indirect way, the maternal parent also has some influence on the sex of the child. There are some genetic and developmental disorders which disrupt the normal activity of the sex chromosomes.
Topic rooms within Genetics
This page has been archived and is no longer updated. By the s, scientists had established methods for staining chromosomes so that they could be easily visualized using a simple light microscope. With this staining method, scientists were able to observe cell division and to identify the steps that occurred during both mitosis and meiosis Figure 1. Arrows indicate the axis along which the cell divides. The first indication that sex chromosomes were distinct from other chromosomes came from experiments conducted by German biologist Hermann Henking in While using a light microscope to study sperm formation in wasps, Henking noticed that some wasp sperm cells had 12 chromosomes, while others had only 11 chromosomes. Also, during his observation of the stages of meiosis leading up to the formation of these sperm cells, Henking noticed that the mysterious twelfth chromosome looked and behaved differently than the other 11 chromosomes. Accordingly, he named the twelfth chromosome the "X element" to represent its unknown nature. Interestingly, when Henking used a light microscope to study egg formation in female grasshoppers, he was unable to spot the X element. Based on his observations, Henking hypothesized that this extra chromosome, the X element, must play some role in determining the sex of insects.
Sex Linked Genes. A particularly important category of genetic linkage has to do with the X and Y sex chromosomes. These not only carry the genes that determine male and female traits but also those for some other characteristics as well. Genes that are carried by either sex chromosome are said to be sex linked. Men normally have an X and a Y combination of sex chromosomes, while women have two X's. Since only men inherit Y chromosomes, they are the only ones to inherit Y-linked traits. Men and women can get the X-linked ones since both inherit X chromosomes. This is due to the fact that men only have one X chromosome. Subsequently, genes on that chromosome not coding for gender are usually expressed in the male phenotype even if they are recessive since there are no corresponding genes on the Y chromosome in most cases. In women, a recessive allele on one X chromosome is often masked in their phenotype by a dominant normal allele on the other.
The XY sex-determination system is the sex-determination system found in humans , most other mammals , some insects Drosophila , some snakes, some fish guppies , and some plants Ginkgo tree. In this system, the sex of an individual is determined by a pair of sex chromosomes. Females typically have two of the same kind of sex chromosome XX , and are called the homogametic sex. Males typically have two different kinds of sex chromosomes XY , and are called the heterogametic sex. In humans, the presence of the Y chromosome is responsible for triggering male development; in the absence of the Y chromosome, the fetus will undergo female development.