Nora had been to see her aunt who was expecting a baby. She was curious to know whether it would be a baby boy or a baby girl. But how can this be found? How is the sex of a child determined ? And is it the same for other animals as well? Let's find out. Sex determination is carried out in various types. The two major types that we will focus on are the genotypic sex determination and the environmental sex determination. Let's begin with the first type. That is the genotypic method. In this type, the sex of a child is determined by the sex chromosomes. We know what sex chromosomes are. In humans, for example, the last pair is the sex chromosomes, while the first 22 pairs are called autosomes. Similarly, in many other organisms the sex chromosomes help to decide the sex of an individual. Let's take an example of mammals. In most of them, including humans the sex of a child is determined by the sex chromosomes namely 'X' and 'Y'. We know that in humans, individuals with both 'X' chromosomes are females while those with '1 X' and' 1 Y' are males. This is one type of genotypic sex determination. Now, let's take the case of birds. It is similar to the case of humans. But only that their system is reversed. In the case of birds, the females have two different sex chromosomes, while males have both similar chromosomes. We use the letters 'Z' and 'W' to represent the chromosomes in them These letters are used just in order to avoid any confusion with our human chromosomes. So a female is the one with 'ZW' and a male is the one with 'ZZ' set of sex chromosomes. So the sex of the birds' offspring is dependent on females. If the mother gives her Z chromosome, then it will be a male, with “ZZ” chromosomes, while if the mother gives a 'W' chromosome, then it will be a female with 'ZW' chromosomes. So just like in the case of humans in birds as well, the sex of the offspring is determined by the sex chromosomes. Wasn't this interesting ? Now let's understand the other types of genotypic sex determination in the upcoming part. Humans and birds have an amazing genotypic sex determination method. The presence of a different sex chromosome plays the vital role in determining the sex of the offsprings. Now let's discuss the third type of genotypic sex determination. In this case, just like humans here we have the sex chromosomes 'x' and 'y'. But the presence of a 'Y' chromosome has got nothing to do with the sex of the child. In fact, the sex chromosomes are not the only factors instrumental in deciding the sex of the child. It is the ratio of the sex chromosomes to the autosomes that decides the offspring to be a male or a female. And which organisms exhibit this pattern of Sex determination? One example is the common fruit fly or the Drosophila melanogaster. But what exactly is this ratio system? It's the ratio of sex chromosomes to the autosomes that determine the sex of the offsprings. For example, when a fly has 'two x' chromosomes and two sets of autosomes , then the ratio obtained will be two is to two, which is one! The flies with this ratio of 1 are females. A Fly with the ratio of 0.5 is male. So in case a fly, has one X and one Y and two sets of autosomes, then the ratio will be 1 is to 2 making the fly a male Now tell me, what if a fly has 3 sex chromosomes, XXY and two sets of autosomes, will it be a male or a female? Give it a shot! Let's crack this together. If we calculate aptly, then there are two x chromosomes and two sets of autosomes Thus, the ratio obtained is 2 is to 2, that's one. So this fly will be a female. The presence of the Y chromosome does not affect the sex of this fly. It's the ratio of the X chromosomes to the autosomes that determines the sex. Now let's talk about one more interesting type of sex determination that makes use of genes. This system is called the haplodiploid system Can you guess what the system could be? Well, let me help you. The haplodiploid system is the one in which the males are haploid as they develop from unfertilized eggs. And females are diploid as they develop from fertilized eggs. This system in which males are haploids and females are diploids is called the haplodiploid system. This system is predominantly found in the lower members of the animal kingdom like insects. Bees, wasps and ants exhibit Haplodiploidy. There are a few more types of genotypic sex determination prevailing in nature. But for now, we will deviate towards the next type of sex determination, which is environmental sex determination. Let's learn about that in the next part. What will happen to water if kept at 0 degree Celsius or at 100 degrees Celsius? At 0 degrees the water will freeze to form ice, while at 100 degrees it will start to boil. But... Do you think temperature effects only nonliving objects? Nope, it has a huge impact on the life of living beings as well. Apart from regulating various body systems, it has a huge influence on several important processes of nature. Take sex determination, for example In certain animals, the sex of the offsprings is dependent on the temperature at which the eggs are incubated. We note that sex determination occurs in two major ways. One is genotypic sex determination and the second is environmental sex determination. So temperature dependent sex determination is a type of the latter form. Let's look at this type in detail. To begin with the sex of the offsprings in some animals is dependent on environmental factors. The first type is temperature dependent sex determination. In some reptiles like crocodiles and alligators the sex of the offspring depends on the temperature at which the eggs incubate. If the temperature is high then the offspring is female, while if it's a low temperature then the offspring is a male. Same is the case for certain turtle species. If their eggs are incubated above 32 degrees Celsius then all develop as females, while if incubated below 28 degrees Celsius then all develop as males. Apart from temperature dependency what other environmental factors determine the sex of an offspring? Well location is one thing. Yes, you heard me right... but location of what? To understand this let's take the example of the green spoon worm. There are two possibilities where these free-floating larvae can land. If the larvae land on the bare ocean floor then they turn out to be females and on the other hand if they land on the body of a female then that makes the larvae turn into a male. This is how location helps determine the larvae sex. Isn't this type of sex determination interesting ? To revise in a nutshell sex of offsprings in various animals is determined by two major types one is the genotypic method and the other is using environmental factors. The genotypic method involves the sex chromosomes that determine the sex of the offsprings. Just like the XX and the XY system in humans or the ZZ and the ZW system found in birds. Another type in this category is the ratio of sex chromosomes to the autosomes which is seen in lower animals like Drosophila melanogaster. The second type of sex domination system is the environmental system. Animals, like crocodiles alligators and turtles exhibit the temperature-dependent sex determination, while lower animals like the green spoon worm, exhibit the location dependent sex determination. So this was about the sex determination system found in various organisms. To know more fascinating things in genetics tune into our upcoming videos. And do not forget to subscribe to our channel to receive more interesting videos.
