Sexual reproduction involves the production of male as well as female gametes. They can be of the same individual or different individuals of two distinct sexes.
- Male and female gametes fuse to produce a new individual from the zygote.
- It is a very complex process and contains less energy efficiency than asexual reproduction.
- Male gametes are known as sperm or pollen grains, and female gametes are known as eggs or ova.
Three Types of Reproductive Cycle in Plants
- Annual Plants: These plants take one year to complete their life cycle from seeds to a mature plant. They must be replanted every year from seeds. And these plants often have bright flowers that attract pollinators—E.g, Marigold, Sunflower, Tomato, etc.
- Biennial Plants: These plants take two years to grow into a mature plant. In the first year, they develop leaves, stems, and roots. And in the second year, they produce flowers, fruits, and seeds before the plant dies—E.g, Parsley, Onion, Celery, Turnips, etc.
- Perennial Plants: These plants can live more than two years or can live for many years, if animals and poor weather do not kill them. After maturity, they produce flowers and seeds every year. They can survive in winter or dry seasons because of their persistent roots, rhizomes, or bulbs—E.g, Rose, Lavender, Mango, Asparagus, etc.
Two Types of Reproduction Cycle in Animals
- Seasonal: The animals that reproduce at a particular time of the year. E.g., Deer, Lizards, Frog, etc.
- Continuous: The animals that reproduce throughout the whole year and get a child throughout the year. Apart from this, in a constant reproductive cycle, a female mates with a male then the reproductive phase starts. In which females go through the cyclical changes and produce a new individual in a defined time interval—E.g, Humans, Chimpanzees, Gorillas, Gibbons, etc.
Mammals exhibit two cycles.
| Oestrous Cycle | Menstrual Cycle |
| It happens in non-primates mammals such as dogs, cows, horses, rats, and mice. | It happens in primates mammals such as apes, humans, and monkeys. |
| If there is no pregnancy then endometrium is reabsorbed by the uterus. | If there is no pregnancy then endometrium sheds through menstruation. |
| There is no heavy bleeding, and can be slightly spotting. | It causes heavy bleeding and is called the bleeding phase. |
| At an estrus period sexual receptivity occurs. | It does not occur sexual receptivity. |
| It is a less complex process. | It is a more complex process. |
| In this process copulation occurs. | In this process copulation does not occur. |
Various Events of Sexual Reproduction and It’s Types
- Pre-fertilisation
- Fertilisation
- Post-fertilisation
What is Pre-fertilisation?
Pre-fertilisation is the process in which gametes are formed and transferred through the following steps:
Step 1: Gametogenesis: In this step, male and female gametes are formed. And gametes are haploid that mean, which contain half the number of chromosomes. So, when two different gametes fuse, they create a zygote.
- Mitotic division takes place in haploid parental bodies such as Bryophytes, Monera, Fungi, and Algae.
- Meiotic division takes place in diploid parental bodies such as Gymnosperms, Angiosperms, Human beings, and Animals.
Gametes are of two types:
- Homogametes/Isogametes: These gametes are similar in size as well as appearance and cannot be easily distinguished between male and female gametes. E.g., Cladophora
- Heterogametes: These gametes can easily be distinguished as male and female because they are not similar in size and appearance.
Heterogametes are of two types:
- Anisogamous: Male as well as female gametes are motile. In this, female gametes are bigger than male gametes. E,g., Chlamydomonas.
- Oogamous: Female gametes are non-motile and larger. Male gametes are motile and smaller in size. E.g., Human beings.
Step 2: Gamete Transfer: It can be done when a female and a male gamete come close to each other and take part in fertilisation. This process is known as pollination in plants and copulation in animals/human beings. The gametes that are motile move through the medium and fused with other gametes to form a zygote.
In algae, bryophytes, and pteridophytes, the water is a medium that transfers a gamete. Mostly, male gametes are motile and undergo heavy loss during transport. So, because of this, male gametes are formed a thousand times more than female gametes.
What is Fertilisation?
The fusion or mating of a male and a female gamete is defined as fertilization. It is a very complex process and requires high energy efficiency. It forms a diploid zygote that further develops into the embryo and has a full set of chromosomes, i.e., 46. This process is also known as Syngamy.
Fertilisation has two types:
- Internal: It happens inside the body of an individual, and male gametes are produced in greater numbers than female gametes. E.g., Birds, Mammals, etc.
- External: It happens outside the body of an individual, and a very high number of gametes are produced in the medium—E.g, Amphibians, Bony Fish, etc.
What is Post-fertilisation
In this stage, the embryo is formed and goes through a further development phase to become a mature organism. And the process is called embryogenesis.
Embryogenesis has the following process:
- Zygote
- Mitosis
- Increase the number of cells
- Cell differentiation
- Modified cells
- Tissues
- Organs
- Organisms
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