Human fertilisation is the union of a human egg and sperm, occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilized egg, initiating prenatal development. The type of reproduction beginning from the fusion of male and female gametes is known as sexual reproduction. In this process of sexual reproduction, a male and a female gamete (reproductive cells) fuse to form a single cell called Zygote This zygote gradually develops into an adult, similar to the parents. The individual that grows from a zygote, receives the character of both the parents
Gametes are an organism’s reproductive cells. They are also referred to as sex cells. Female gametes are called ova or egg cells, and male gametes are called sperm. Gametes are haploid cells, and each cell carries only one copy of each chromosome. These reproductive cells are produced through a type of cell division called meiosis. During meiosis, a diploid parent cell, which has two copies of each chromosome, undergoes one round of DNA replication followed by two separate cycles of nuclear division to produce four haploid cells. These cells develop into sperm or ova. The ova mature in the ovaries of females, and the sperm develop in the testes of males. Each sperm cell, or spermatozoon, is small and motile. The spermatozoon has a flagellum, which is a tail-shaped structure that allows the cell to propel and move. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilisation, a spermatozoon and ovum unite to form a new diploid organism.
What is sperm:
In simple terms, sperm is the male sex cell or gamete. The human sperm cell is haploid so that its 23 chromosomes can join the 23 chromosomes of the female egg to form a diploid cell with 46 paired chromosomes. Humans produce motile sperm with a tail known as a flagellum, which is known as spermatozoa.
Structure of Sperm:
The sperm consists of a head, neck, middle piece, and tail.
The Head contains acrosome apically, which contains enzymes that facilitate the entry of sperm into the ovum. It is followed by an elongated nucleus (haploid). The neck or connecting piece contains one typical centriole and one atypical centriole such as the proximal centriole. The middle piece has multiple mitochondria that provide energy for the movement of sperms. The tail is a flagellum that protrudes out of the cell body and is responsible for the vigorous motility of sperms. The tail helps sperm in swimming so that they can reach toward the ovum. Around 200-300 million sperms are ejaculated at once.
What is ovum?
Also called the egg cell or ova in the plural, it is the female gamete or reproductive cell present in humans. Ovum is non-motile and when the egg or ovum fuses with sperm during fertilisation, a zygote or a diploid cell is formed that can grow further into a new organism. Sometimes, the young ovum of an animal is termed an ovule. It is one of the largest cells in the human body and is visible even to the naked eye without the help of a microscope. It measures approximately 0.1 mm in diameter in humans.
Structure of ovum:
Ovum has a cell substance at its center called the yolk or ooplasm. Ooplasm contains a nucleus named the germinal vesicle and also a nucleolus called the germinal spot. Ooplasm has formative yolk and nutritive yolk, the formative yolk is the cytoplasm of an ordinary animal cell and the nutritive yolk (deutoplasm) is made of rounded granules composed of fatty and albuminoidal substances in the cytoplasm. The latter helps in nourishing the embryo in the early stages of the developmental phase in mammals.
Fertilisation:
Human fertilisation is the union of a human egg and sperm. Occurring in the ampulla of the fallopian tube. The result of this union leads to the production of a zygote cell, or fertilised egg, initiating prenatal development. The process of fertilisation involves a sperm fusing with an ovum. The most sequence begins with ejaculation during copulation followed by ovulation, and finishes with fertilisation.
In mammals, the egg is protected by a layer of an extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reaction, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. Fusion between the oocyte plasma membrane and sperm follows and allows the sperm nucleus, centriole, and flagellum, but not the mitochondria, to enter the oocyte. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome. This process ultimately leads to the formation of a diploid cell called a zygote. The zygote divides to form a blastocyst and, upon entering the uterus, implants in the endometrium, beginning pregnancy.
Conclusion:
In Sexual Reproduction there exist two types of gamete one male and one female. The male gamete is known as Sperm and the female gamete is known as Ovum. These gametes are created by the meiosis division of Human Cells so in that process, they will always have half the number of genes that a parent Cell contains, for which they are called haploids.