Asexual and Sexual Reproduction: Types and Cycles

Asexual Reproduction

Asexual reproduction involves a single individual or vegetative parts giving rise to new organisms through mitosis. These offspring are genetically identical and are considered clones. There are several types:

• Bipartition: Organisms divide through a typical mitosis process, resulting in two new individuals of the same size.
• Budding: Daughter cells are formed of different sizes. During mitosis, a bud forms on the parent body, and one of the nuclei migrates to it. When the bud separates, it forms two cells, one larger than the other.
• Multiple Division: Multiple daughter cells are formed. The nucleus of the stem cell divides repeatedly by mitosis, forming a multi-core structure. The cytoplasm is shared, and each core is surrounded by a membrane. The stem cell ruptures, releasing all the daughter cells.

Sexual Reproduction

Sexual reproduction involves fertilization through the union of specialized cells, called gametes, from two progenitors. Gametes are haploid, and when united, they give rise to a diploid cell, the zygote. Gametes are of two types, male and female, which determines the sex of the organisms.

Organisms with separate sexes are called unisexual (in the case of animals) or dioecious (in the case of plants). Organisms that can form gametes of both types are called hermaphrodites or monoecious. Most flowering plants and snails are hermaphrodites.

Biological Cycles

A biological cycle is the set of events that occur from the formation of a zygote until it arises again. There are three main types:

• Haplontic Cycle (Zygotic Meiosis): Meiosis occurs just after the formation of the zygote, which is the only diploid stage. Therefore, most of the time, the organisms are haploid. This is common in less developed organisms.
• Diplontic Cycle (Gametic Meiosis): Meiosis occurs only in cells that will result in gametes. Therefore, the organisms are diploid, and only the cells responsible for reproduction are haploid. This occurs in all animals.
• Diplohaplontic Cycle (Sporic Meiosis): This is a combination of the previous cycles. From a diploid adult organism called a sporophyte, cells are formed by meiosis that are not gametes, called meiospores. Meiospores form gametophytes. These give rise to gametes, which in this case are formed by mitosis because the gametophytes are haploid. The union of gametes would lead back to the sporophyte, restarting the cycle.