According to the Big Encyclopedic Dictionary, heterogamy is a sexual process in which female and male gametes, which merge during the process of fertilization, are different in size and shape.
The main types of sexual process
Isogamy, heterogamy, oogamy are all processes of sexual fusion of cells. Isogamy is the most primitive form of the reproductive process in which male and female cells are the same size and are morphologically identical. Such a merger is inherent in the simplest fungi and green algae of the same species.
Heterogamy is a sexual process in which sex cells (gametes), absolutely different in size and morphological structure, merge.
Oogamy is an order of magnitude different process of sexual fusion of cells, in which germ cells are very different from each other. This type of sexual process is inherent in humans, as well as some mammals. Fertilization of this type occurs between a large female reproductive cell and a small male cell compared to it. Most often, the female cell is motionless, while the male cell is actively moving. This process can occur both inside the female body and beyond.
It is believed that there are two sexes: male and female. It should be noted, as we already know, that in nature there are three types of sexual reproduction: isogamy, heterogamy, oogamy. In all cases, complementary germ cells form, but only with oogamy an egg and sperm are formed.
Types of sex determination
There are several types of sex determination of future offspring. Three main methods are most often used: program, singam, metagam. The most accurate of them is considered to be the programmatic determination of the sex of future offspring. These studies must be carried out before the process of fertilization (ontogenesis). So, for example, if we take the study of the sexual process of rotifers, then they have the ability to form eggs of different sizes. Scientists have found that females develop from large eggs, and only males from small ones.
Determining sex directly during the sexual process of fertilization is syngamous. The analysis is based on the selection of sex chromosomes. This type is the most common. Heterogamy is the main sexual process for the syngamous type of determining future offspring.
The metagamic or epigamous type of sex determination does not depend on the shape of germ cells, nor on their size, nor even on the number of chromosomes. The determining factors for this type of research are environmental factors, as well as the intensity of their impact. This type of determination of gender can be considered as modification variability.
Examples of the influence of external factors
The simplest and most common way to control the sex of future offspring can be seen in the example of crocodile eggs. Both in natural conditions and when creating artificial temperature conditions, at a certain temperature either females or only males are born. It depends on the temperature.
There are also known cases where the gender of future offspring is affected by the conditions in which they develop. Bonellia viridis is a species of ringed sea worm that has very specific abilities to change sex depending on its habitat.
Varying degrees of influence of certain factors
Both the genotype and a number of external factors affect the sex of the future organism almost equally. However, in different organisms, the degree of influence of external factors and genotype on the sex is different. The genotype is decisive for the future sex of the offspring in humans and most mammals. This kind of sexual process, such as heterogamy, examples of which were described earlier, primarily refers to people. External factors do not affect this process. At the same time, the same Bonellia viridis (a variety of ringed sea worm) described earlier, or fish, are completely dependent on changes in the external habitat.
The female of these worms is significantly larger in size than her male, which has microscopic dimensions. He lives right in the female genital tract. The larvae are bisexual, that is, they have signs of both sexes. That is why environmental factors are more likely to influence the sex of future offspring . Thus, a larva that freely lives in the water column will become a full-fledged female of a large size. However, if she meets a female, which will be free from the male, she can fix on her and eventually become a male.
It happens that the gender of the offspring of some mammals is affected by external factors. In cattle, identical twins appear as a result of heterogamy. Even in the case when the cow simultaneously develops heterosexual twins, the goby will be normally developed, while the male heifers may show both male and female sexual characteristics. This feature is due to the fact that male sex hormones are secreted earlier than female and therefore can affect the sex of their twin. This example clearly shows the influence of external factors on the future sex of the offspring.
From the above it follows that the base and biological basis of any change, including gender, is the original bisexuality of the body’s genetic code. It is this feature that proves the fact that sex can change as a result of the development of the body. And heterogamy is one of the main confirmations of this statement.