Table of Contents
What is Sexual Reproduction?
Sexual reproduction involves the fusion of haploid gametes. It is defined as a mode of reproduction in which a diploid zygote is formed after the fusion of the male and female haploid gametes. Later, the zygote is developed into a new offspring that is not identical to the parent organisms.
Sexual reproduction differs from asexual reproduction where an organism can reproduce without fertilization. Therefore the offspring is a clone of its parents. In the case of sexual reproduction, fertilization is a must for zygote formation and the offspring develops with distinct genetic characters. Sexual reproduction can be divided into two types- Syngamy and conjugation
Sexual Reproduction Definition
A process of producing individual offspring by parents is called reproduction. It is the crucial process for the survival of all living organisms, they increase their number by reproducing by different means. Sexual reproduction is also a type of reproduction where two parents are involved. In this process, a fusion of two haploid gametes results in a diploid organism.
Sexual Reproduction Etymology
The word reproduction is made up of two Latin words, re meaning “again” and production meaning “to produce”.The word sexual is derived from the Latin word sexualis, meaning “copulation or generation”. Sexual reproduction is also called syngenesis.
Sexual Reproduction and Asexual Reproduction
The process of reproduction is divided into two types-
Sexual reproduction and Asexual reproduction.
Sexual Reproduction includes gametogenesis and fertilization that results in a diploid zygote formation. The incorporation of cell division is called gametogenesis. It starts with mitotic division then the daughter cells undergo reduction division (meiosis) to produce haploid gametes. The female carries haploid eggs whereas the male carries haploid sperm cells. After the sexual intercourse, the sperm cell comes closer to the egg cell resides in the ovum of the female for the union. The process proceeds with the combination of the genetic material of sperm and egg, which is called fertilization. The diploid zygote then undergoes mitotic divisions to form an embryo.
Asexual Reproduction has some differences as compared to sexual reproduction. It does not require two parents and also does not undergo the process of fertilization. The process of meiosis is also not present. The individual produces an offspring that is genetically identical to its parent.
Types of Sexual Reproduction
Sexual reproduction is divided into two types that are syngamy and conjugation. The fusion of haploid sex cells that results in the formation of the diploid zygote is called syngamy. It is a synonym for fertilization. It is a common type of reproduction adopted by higher plants and animals.
Conjugation includes the process of coming together of two organisms in a temporary fusion. The fusion completes by a cytoplasmic bridge. It is adopted by microorganisms or single-celled organisms such as bacteria, protozoans, etc.
Sexual Reproduction in Single Celled Organism
Various single-celled organisms such as bacteria and protozoans reproduce sexually by the method of conjugation. Conjugation is the process where two bacterial cells transfer their genetic material by a plasmid. In the bacterial cell, the plasmid is a part of the chromosome.
Bacteria also use conjugation to acquire a beneficial gene for survival. Conjugation is also used by some protozoans in which two protozoan cells come together to transfer their genetic material. After separation, each of the cells becomes a fertilized cell. Conjugation is also seen in some algae and fungi species.
Viruses also show some evidence to reproduce sexually by genetic recombination method, but sexual reproduction in viruses is not studied properly and is still contested.
Syngamy in Multicellular Organisms
The multicellular organisms including humans reduce sexually by syngamy. It completes in two steps- plasmogamy and karyogamy. Plasmogamy refers to the union of cytoplasms of two gametes. In the next step, the fusion of the nuclei of two gametes occurs which is called karyogamy. The union results in the formation of a diploid zygote. The zygote undergoes series of mitotic divisions to form an embryo. Syngamy is also classified into many types.
The plant completes its life cycle in two generations, the gametophyte, and the sporophyte generation. The gametophyte generation starts with a haploid spore that produces a haploid gametophyte. Sex organs are present in the haploid gametophyte that participates in the fertilization process.
A diploid zygote is formed after fertilization. The zygote develops into a sporophyte from which sporophyte generation starts. It produces spores in a specific organ called sporangium. Higher plants bear the sex organ called flower that can be unisexual or bisexual.
The pistil is a female organ and anther is a male reproductive organ in plants. The pollen grains are present in another that bears sperm cells. The ovary is located in the pistil that has egg cells in the ovule.
The transfer of pollen grains to the ovule is called pollination. Pollination can occur by different means such as self-pollination, cross-pollination. It results in the formation of a diploid zygote. Later the zygote develops into an embryo and endosperm from a nutritive tissue called a seed.
Most of the animals are unisexual and reproduce by mating with another organism. They display sexual dimorphism, sexual selection, and courtship rituals. The occurrence of two sexually distinct forms of an organism is referred to as sexual dimorphism. For example, male birds have more attractive features than female birds.
Humans can reproduce naturally by sexual means only. The process includes several courtship rituals, copulation, pregnancy, childbirth, and parental care. The internal fertilization takes place after intercourse which results in a diploid zygote.
The zygote undergoes mitosis and forms an embryo. The embryo develops into a fetus that receives nutrients from an umbilical cord. The pregnancy period or gestation period is of 9 months or almost 266 days. Childbirth is followed by parental care.
Advantages of Sexual Reproduction
There are several advantages of sexual reproduction. The number of chromosomes remains across generations. For example- humans have 46 chromosomes half comes from each of the parents, before fertilization the haploid gametes are formed by meiosis. Therefore after fertilization, they keep the number of chromosomes like the somatic cells. Sexual reproduction also improves the gene pool. It performs syngamy thus helping to maintain genetic diversity.
Sexual Reproduction Citations
- Exceptionalism is not exceptional in relation to sexual and reproduction mechanisms: Contrasts of human and animal sexuality. Clin Anat . 2017 Oct;30(7):940-945.
- The separation of sexual activity and reproduction in human social evolution. Adv Exp Med Biol . 2014;814:159-67.
- Endocrinology of human female sexuality, mating, and reproductive behavior. Horm Behav . 2017 May;91:19-35.
- The State of Adolescent Sexual and Reproductive Health. J Adolesc Health . 2019 Dec;65(6S):S3-S15.