Sexual Reproduction in Animals and Plants

As we have previously mentioned, sexual reproduction is a type of reproduction where there is a fusion of gametes, resulting in an offspring that is genetically different to its parents.

The characteristics that define this type of reproduction are various. In the first place, in sexual reproduction there are two individuals involved, unlike asexual reproduction, a female and a male. Both some and others have organs known as gonads that produce gametes. These gametes are the sex cells, ovules in females, generated by the ovaries and sperm produced by the testes in males.

When an egg and a sperm fuse, they give rise to a zygote. This union is called fertilization. Fertilization can occur inside or outside the animal, depending on the species, thus there is external fertilization where females and males expel their gametes to the aquatic environment to fertilize them and internal fertilization, where the sperm find the ovule inside the female.

After fertilization, the formed zygote will have 50% maternal DNA and 50% paternal DNA, that is, the offspring that are produced through sexual reproduction will have genetic material from both parents. In some cases, such as in certain insects and reptiles, temperature can influence the sex of the offspring, showcasing the diversity of reproductive strategies among animals. Check out the video below to learn more about sexual reproduction!

Sexual reproduction in animals consists of several stages, beginning with gametogenesis. This phenomenon consists of the formation and development of the female and male gametes within the female and male gonads respectively.

From germ cells and through a type of cell division known as meiosis, both females and males create their gametes. The rate of creation and maturation of gametes will depend on several factors, but mainly on the species and the sex of the individual.

After gametogenesis, the mechanism by which fertilization occurs is mating. Mediated by hormones, individuals of childbearing age will seek the company of the opposite sex to mate and, after courtship, copulation will occur in those animals that have internal fertilization. Species with external fertilization will release the gametes to the environment for fertilization.

After fertilization, the last phase of sexual reproduction occurs which consists of a series of molecular changes that allow the nucleus of the ovum to fuse with the nucleus of the sperm. These changes ensure genetic diversity, which is crucial for adaptation and survival in changing environments. You should also check out our article about the different modes of reproduction in animals.

The types of sexual reproduction in animals are related to the size of the gametes that are going to unite in fertilization, thus we find isogamy, anisogamy and oogamy.

• Isogamy is the fusion of two gametes of similar size, it is not possible to visually differentiate which is the male or female gamete. Both one and the other can be mobile or immobile. It is the first type of sexual reproduction to appear in evolutionary history and is typical of chlamydomonas (single-celled algae) and monocystis, a protist. It does not occur in animals.
• Anisogamy is the fusion of gametes of different sizes. There are differences between male and female gametes, and both can be motile or immobile. It appears later in evolution than isogamy. It occurs in fungi, higher invertebrates, and other animals. Notably, anisogamy allows for a greater allocation of resources to the larger gamete, often providing it with more nutrients.
• Oogamy is the fusion of a very large, immobile female gamete with small, mobile male gametes. It is the last type of reproduction to appear in evolution. It is typical of higher algae, ferns, gymnosperms, and animals such as vertebrates. This form of reproduction is predominant in animals and provides the egg with ample resources to support the developing embryo.

There are as many examples of sexual reproduction as there are animal species:

• Mammals such as dogs, chimpanzees, whales or humans have sexual reproduction with internal fertilization and oogamy. They are also viviparous animals, so embryonic development will take place in the womb.
• Birds, although they lay eggs as they are oviparous animals, also follow this sexual reproductive strategy with oogamy. Their mating rituals are often complex and vary widely among species.
• Reptiles, amphibians, and fish also reproduce sexually, although certain species follow an asexual strategy at certain times in their lives. Some are oviparous and others ovoviviparous, many of them have external fertilization and many others internal. For instance, frogs often engage in elaborate mating calls to attract partners.
• Arthropods are a large and diverse group of animals, so in this group we will find both internal and external fertilization and cases of oogamy and anisogamy. Some will be able to reproduce asexually. Insects like butterflies exhibit fascinating courtship behaviors during the mating process.

Do not forget that there are hermaphroditic animals, with female and male reproductive organs at the same time, but they can only act as female or male when mating. Selfing does not occur. Additionally, some species like corals can switch reproductive strategies depending on environmental conditions.

Just like animals, plants also have two types of reproduction, asexual and sexual reproduction. In their sexual reproduction, plants fuse two gametes together to create an offspring. However, unlike animals, plants are immobile and therefore reproduce sexually in a different way than animals. We will take a deeper look into the different ways animals do this later on in this article.

In some plants, pollination can occur with the help of wind, water, or animals, ensuring the transfer of pollen from one flower to another. We also encourage you to check out this video about sexual reproduction in plants!

Sexual reproduction involves two fundamental processes:

• Meiosis which rearranges the genes and reduces the number of chromosomes.
• Fertilization which restores the chromosome to a complete diploid number.

Different types of plants and algae vary in these processes, but many of them, including all land plants, undergo alternation of generations. They do this with two different multicellular stages, haploid containing a single set of chromosomes in each cell.

The gametophyte produces male or female gametes (or both), by a process of cell division, called mitosis. In vascular plants with separate gametophytes, female gametophytes are known as mega gametophytes and the male gametophytes are called micro gametophytes.

The fusion of male and female gametes, known as fertilization, produces a diploid zygote, which develops by mitotic cell divisions into a multicellular sporophyte. The mature sporophyte produces spores by meiosis. This is sometimes referred to as “reduction division” because the chromosome pairs are separated once again to form single sets. This cycle ensures genetic variation and adaptability among plant populations.

Spores

Certain plants can reproduce sexually or asexually through spores. The spores are often located on the underside of the leaves and are carried to a new area by wind or rain. Spores, unlike seeds, are less likely to be eaten by animals, but they are at risk of being consumed by bacteria and fungi. Spores are an efficient way of colonizing new environments due to their lightweight nature.

Flowers

Other plants will reproduce through the stamens in their flowers, this includes all flowering plants. This will be done by pollination as animals come to pollinate the stamen from other plants, allowing the ovule to be fertilized and start developing their seeds. Pollination strategies can range from wind dispersal to intricate relationships with specific animal pollinators. We also encourage you to check out our article about 15 animals that pollinate.

Cones

Cones are the parts of conifers which contain reproductive structures. Female cones produce ovules and male cones, which are much smaller and not as visible, produce pollen. Once the female cone is fertilized it'll become a seed. Male and female cones are usually produced from the same plant to facilitate cross-fertilization and to avoid self-fertilization. This mechanism helps maintain genetic diversity in these plant species.

Fruit

Fruit is the result of the maturation of one or many flowers, and is therefore only found in angiosperms. In botany, fruit is considered the ripened ovary of a seed-bearing plant which contains its seeds. In flowering plants, as a seed develops, its ovary begins to ripen and the ovary wall becomes fleshy (such as in berries and apples) or forms a hard outer covering (such as in nuts). Fruits play a crucial role in seed dispersal, often attracting animals that aid in spreading seeds over large areas.

Seeds

Seeds can be dispersed by the wind, water, or animals. Seeds are a more evolutionarily advanced form of plant reproduction than spores and are present in both gymnosperms and angiosperms. However, seeds can sometimes be eaten by animals. The protective coating of seeds is an adaptation to ensure the survival of the embryonic plant until conditions are favorable for germination.

There are thousands of examples of sexual reproduction in plants, so here are some examples of large groups of plants that reproduce sexually:

• Ferns, such as horsetails or club-molasses, which reproduce through spores. These plants thrive in moist environments where their spores can easily disperse and germinate.
• Gymnosperms, such as the Maidenhair tree or the Scots pine, which reproduce through seeds. These plants are often found in colder climates where their seed cones provide protection against harsh weather conditions.
• Angiosperms, also known as flowering plants, such as orchids or flower heads, which reproduce through seeds. They are the most diverse group of plants and have developed elaborate flowers to attract pollinators.

If you found this article interesting you can continue learning about our world with out article about the 5 different animal kingdoms.

If you want to read similar articles to Sexual Reproduction in Animals and Plants, we recommend you visit our Facts about the animal kingdom category.