The sexual reproduction involves syngamy or fertilization ie fusion gametes male and female to produce a zygote that will form the developed in embriofitas one embryo and this in turn a new plant. Its importance is due to the fact that paternal and maternal characteristics are combined in the zygote, resulting genetically different to each of the parents.
Definition
For gametes to originate from somatic cells, a reductional division called meiosis has to occur at some point in the life cycle, which produces four daughter cells from each stem cell with the chromosomal number reduced by half (gametic number). If this did not happen, and the gametes had the same number of chromosomes as somatic or vegetative cells, the number of chromosomes would double with each fertilization.
In sexual reproduction three different processes take place:
- Gametogenesis: Gamete formation process; 4 gametes are formed from a stem cell.
- Fertilization: Two gametes from different individuals fuse (their cytoplasms and nuclei unite) creating a new cell called the zygote.
- Embryonic development: Processes by which a zygote transforms into an adult.
Classification and characterization
The morphological and functional characteristics of the gametes make it possible to differentiate two forms of sexual reproduction: isogamous (type of sexual reproduction in which morphologically equal gametes are involved, hereditary transmission is through the mother) and anisogamic.
Isogamic sexual reproduction is observed in some algae, lower fungi , and protozoa. In this type of reproduction, the gametes have the same size, identical external shape and the same physiology . For this reason, it is not possible to call them male and female gametes, so the symbols + and – are used depending on their behavior.
Anisogamic or heterogamous sexual reproduction is the most common, and is used by most multicellular organisms. In it, the gametes differ both morphologically and physiologically. One of them is tiny and mobile, receiving the name of the male gamete or microgamete, while the other is large and sedentary and is called the female gamete or macrogamete. Currently with the new nomenclature, the microgamete is known as the sperm and the macrogamete, the ovule .
Advantages and disadvantages
Sexual reproduction presents certain disadvantages with respect to asexual reproduction , among which are: greater energy expenditure in the search and struggle to find a mate, slower reproduction and fewer offspring, among others.
On the contrary, they have the biological advantage of promoting genetic variation between the members of a species, since the offspring is the product of the genes contributed by both parents, instead of being a genetic copy. The greater the genetic variability of a population, the greater its rate of evolution; a population with considerable amounts of genetic variability can protect itself against future environmental changes, since if it changes there may be a minority form that benefits from it; each generation exposes new allelic combinations to natural selection.