The Sex of Offspring Is Determined by Particular Chromosomes: Not Sex Assignment At Birth

Sex determination in humans: Human body cells have 23 pairs of chromosomes in the nucleus.

Twenty two pairs control most of the characteristics. Pair 23 are the sex chromosomes.

They carry genes that determine an embryo's sex - whether offspring are male or female:males have two different sex chromosomes, XY females have two X chromosomes,

XX,These photographs show all the chromosomes aligned in pairs.Chromosomes from a maleThe blue box shows the two sex chromosomes - these are different sizes, therefore an X (larger chromosome) and a Y (smaller one).The Y chromosome carries a gene called SRY.

It causes the testes to develop. They produce male sex hormones which cause male characteristics to develop. If they are not present female characteristics develop.

(What is the assignment of sex at birth) “Sex assigned at birth” means the male or female designation that doctors ascribe to infants based on genitalia and is marked on their birth records.

Sex assigned at birth is intended to displace the concept of “biological sex.”As often happens during a lengthy course of discovery, scientists observed and described sex chromosomes long before they knew their function. In humans and many other animal species, sex is determined by specific chromosomes. How did researchers discover these so-called sex chromosomes? The path from the initial discovery of (sex chromosomes in 1891) to an understanding of their true function was paved by the diligent efforts of multiple scientists over the course of many years. As often happens during a lengthy course of discovery, scientists observed and described sex chromosomes long before they knew their function. How is sex determined in human beings?: There are two pairs of sex chromosomes. One of the sex chromosome is inherited to the offspring by the mother and the other is inherited by the father. The mother (females) have two X chromosomes and the father (males) will have X and Y chromosome. The chromosome which is inherited by the mother will be X. The father can inherit X or Y chromosome. If the father inherit Y chromosome, the offspring will be male.https://www.toppr.com/ask/question/how-is-sex-determined-in-human-beings/ ------------------------------------------------------- An idea inspired by the "X element" By the 1880s, 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.The first indication that sex chromosomes were distinct from other chromosomes came from experiments conducted by German biologist Hermann Henking in 1891. 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. However, he was unable to gather any direct evidence to support his hypothesis,Based on his observations, Henking hypothesized that this extra chromosome, the X element, must play some role in determining the sex of insects. However, he was unable to gather any direct evidence to support his hypothesis.Over time, other scientists studied the appearance of chromosomes in a wide variety of animal species, and it became clear that there was a relationship between the physical appearance and number of chromosomes in gametes and somatic cells from males and females of a given species. --------------------------------------------------------- In humans, females inherit an X chromosome from each parent, whereas males always inherit their X chromosome from their mother and their Y chromosome from their father. Consequently, all of the somatic cells in human females contain two X chromosomes, and all of the somatic cells in human males contain one X and one Y chromosome (Figure 3). The same is true of all other placental mammals — males produce X and Y gametes, and females produce only X gametes (Figure 4). In this system, referred to as the XX-XY system, maleness is determined by sperm cells that carry the Y chromosome. ----------------------------------------------------------- Many people do not realize, however, that the XX-XY sex determination system is only one of a variety of such systems within the animal kingdom. In fact, sex determination can be very different between different organisms. For example, in the XX-XO system found in crickets, grasshoppers, and some other insects, sperm cells that lack an X chromosome (referred to as O) determine maleness. Here, females carry two X chromosomes (XX) and only produce gametes with X chromosomes. Males, on the other hand, carry only one X chromosome (XO) and produce some gametes with X chromosomes and some gametes with no sex chromosomes at all (Figure 5). ----------------------------------------------------------- Despite the previous examples, males are not always the sex with the mismatched chromosome pair. For example, the ZZ-ZW sex determination system used in birds, snakes, and some insects relies upon females to carry the mismatched chromosome pair (ZW) and males to carry the identical pair (ZZ) (Figure 6). If the three systems discussed above are compared in side-by-side Punnett squares (Figure 7), it is easy to see that sex determination is simply a matter of gamete assortment. Determinations of male and female character arise from a variety of different gamete combination patterns, all of which are the result of gender coding in sexually reproducing organisms.The https://www.nature.com/scitable/topicpage/the-sex-of-offspring-is-determined-by-6524953/variety of inheritance patterns described in this article illustrate that sex determination is a complex and varied feature among organisms. The XX-XY, XX-XO, and ZZ-ZW systems are only a sample of the wide variety of sex determination systems that scientists have documented in the wide world of living beings, however.https://www.nature.com/scitable/topicpage/the-sex-of-offspring-is-determined-by-6524953/ -----------------------------------------------------------