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Every life starts with a zygote.

Every life starts with a zygote. A zygote is a 2n cell formed by the fusion of a sperm and an egg.  The sperm is the male reproductive cell, and the egg is the female reproductive cell. The fusion of these cells is called fertilization, and it results in the production of the zygote. The zygote then proliferates, divides and differentiates into different tissues and organs of the body. All the information on these pathways of cell division and differentiation is encoded in the sperm and the egg. Therefore it is important to study how these cells are formed and the differences in the processes underlying it.

Sperms are considered as the male gametes produced in the testis. The process of sperm production in the male testis is called spermatogenesis. Sperms are produced from the mother cell called spermatogonium. These cells are present in small tubules of the male testis. The spermatogonium is a diploid cell containing 2n chromosomes. The spermatogonium divides into four, haploid (n) spermatozoa. Spermatogonium arises from spermatogenic germs cells. These germ cells are stem cells that have the capability of self-renewing. Differentiation of spermatogenic germ cells results in the formation of intermediate spermatogonium, which further undergoes mitosis to produce type B spermatogonia. These type B spermatogonia further undergo mitosis to produce primary spermatocytes. The primary spermatocytes undergo meiosis I to produce secondary spermatocytes. The secondary spermatocytes then undergo meiosis II and produce four haploid spermatids. These spermatids finally undergo spermiogenesis to produce the sperm tail. Spermatogenesis commences when the males attain puberty and continue for the rest of their lives. Millions of sperms are produced in the process every day. Spermatic development takes place about 70 days in humans.

Eggs are produced in the ovary of females by a process called oogenesis. It is produced from the oogonia present in the ovary. The egg or the ovum is produced from the diploid primary oocyte by meiosis. Two polar bodies are also formed during meiosis I and II. Unlike spermatogenesis that occurs every day, oogenesis occurs once in a month, starting from puberty and ending at menopause. Similar to spermatogonia, the first female reproductive cell is the oogonia, which is a stem cell. Therefore oogonia have the ability of self-renewal and self-differentiation. Thousands of oogonia divide into around seven million germ cells from the second to the seventh month of embryonic development. The oogonia divide by mitosis to produce the primary oocyte. These primary oocytes undergo meiotic division till the diplotene stage in the embryonic stage, after which it stalls the process of cell division and attains a quiescent stage. The cell division process is arrested until the girl attains puberty. Some primary oocytes have also been found to be arrested until 50 years of age. Most primary oocytes are destroyed, and around 400 primary oocytes divide into gametes. Upon attaining puberty, the arrestation on the cell division process is lifted, the process continues, and primary oocytes divide into secondary oocytes. However, this division is unequal, and one secondary oocyte and one polar body are formed from a primary oocyte. The cytoplasm is contained in the secondary oocytes, while the nucleus in the polar body is destroyed. During ovulation, these secondary oocytes are released from the ovary. Spermatogenesis and oogenesis, although taking place in two different individuals, has certain similarities and dissimilarities. The difference between spermatogenesis and oogenesis are as follows.

Apart from these spermatogenesis and oogenesis differences, there are some similarities between the two processes. The similarities between spermatogenesis and oogenesis are:

Spermatogenesis and oogenesis are the two most important processes in life. To distinguish between spermatogenesis and oogenesis is easy since it can be done by their location and the final product. Sperms are small in size, have a distinct tail, which makes it motile. However, an ovum is larger without any tail and is non-motile. These cells contain n set of chromosomes so that when they fuse to form the zygote, the resulting cell becomes diploid (2n). Moreover, these cells are the carriers of the genetic information from the parents to the offsprings, and also contains the information of differentiation of the zygote and the embryo to the different tissue processes. These cells form the basis of hereditary relationships in any organism. Any kind of genetic mutation in these cells might reflect in the process of development, which can be detected as early as in the embryonic stage or might surface at some later stages of life.

Spermatogenesis is the development of the sperm from the spermatogonia.

Oogenesis is the development of ovum from oogonia.

Four haploid sperms are produced after spermatogenesis.

One ovum and two polar bodies are formed after oogenesis.

The three common stages of spermatogenesis and oogenesis are Multiplicative, Growth, and Maturation stages.

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Production of sperm from spermatogonia

All stages of spermatogenesis take place in the testis

The last stage of oogenesis takes in the oviduct.

Sperms are released from the testis

Millions of sperms are produced every day

One ovum is released once per month.

Spermatogenesis takes place every day from puberty until the end.

Oogenesis takes place once per month from puberty to menopause.

Plays a supporting role during the process

Resting stage takes place from the embryonic stage to puberty.

Equal, resulting in the formation of four haploid spermatids

Unequal, results in the formation of one haploid ovum and two polar bodies.

Spermatids are smaller than the spermatocyte

Nuclear condensation takes place in the sperms

No nuclear condensation takes place in the ovum.

Very little food reservation takes place in the sperms

A lot of food and metabolite are stored in the ovum.

Completed in three phases- Multiplicative, growth, and maturation.

Completed in three phases- Multiplicative, growth, and maturation.