Which gamete provides the cytoplasm for the zygote

In sexual reproduction, a male gamete and a female gamete join together. This is fertilisation. Gametes and fertilisation Humans typically reproduce through sexual reproduction. Gamete n. What is a gamete? A gamete is the mature reproductive or sex cell that contains a haploid number of chromosomes i.

The zygote is formed by the fusion or combining of two gametes, i. This union of gametes resulting in a zygote is called fertilization.

Characteristically, one of the gametes is usually larger in size, non-motile. It is known as female gamete or ovum or egg cell. The other gamete cell is motile and smaller in size. It is known as male gamete or sperm cell.

In humans, each gamete contains 23 chromosomes and their fusion results in the formation of a diploid zygote containing 46 chromosomes. In animals, these reproductive cells are produced in respective male and female gonads or reproductive organs. In seed-bearing plants, the male gametes are the pollen while the female gametes are enclosed in the ovules of the plant.

However, in plants, the gamete may or may not be always a haploid cell. What are examples of gametes? What are the different types of gametes? The gametes involved in fertilization can be similar referred to as isogamy or the two gametes may be different referred to as anisogamy. Isogamy : gametes with similar morphology i. Examples: gametes of unicellular algae, Chlamydomonas reinhardtii and Carteria palmata.

Anisogamy : gametes with dissimilar morphology i. The gamete with a smaller size is known as sperm or male gamete whereas the gamete with a larger size is known as ova or egg or female gamete.

Furthermore, these gametes can be motile as well as non-motile. In the case of red algae, Polysiphonia , both the gametes are non-motile. The non-motile sperm fuses with the non-motile egg to form a zygote. Non-motile male gamete or sperm is known as spermatia. This is also seen in certain flowering plants wherein both the gametes are non-motile and are present in the gametophyte. The non-motile male gamete in plants is known as pollen.

Oogamy : in humans and mammals, one of the gametes, male gamete or sperm, is motile and the other gamete, egg, or female gamete is non-motile. This condition is known as oogamy , wherein a large non-motile egg is fertilized or will fuse with a small and motile sperm to form the zygote. Another way of classification of the gametes is based on their size.

Depending on the size, gametes can be categorized as:. During the process of gametogenesis, a diploid 2n cell undergoes meiosis to produce four haploid n cells. In general, the process of gametogenesis usually starts with gametogonia. Gametogonia are derived from the primordial germ cells PGCs. These germ cells proliferate by the process of mitosis. In the late embryonic stage, these cells are transferred to the gonadal ridge where they are known as gametogonia.

Once gametogonia have developed, further gametogenesis will result in the formation of egg or sperm, depending on the sex of the individual. The process of gametogenesis is completely different in males and females. The male reproductive cell or gamete is known as the sperm cell. In animals, anisogamy is seen, wherein the structure of the male gamete is different from the female gamete.

In animals, including humans, sperm is small in size and is motile. The motile organ of the sperm is known as the flagellum. The sperm cells have a limited life span and cannot divide. The sperms in mammals have two distinct structures enclosed in a single membrane Figure 2.

Connecting the two parts, i. Mitochondria is very essential for the sperm cell as it provides all the energy for the movement of the sperm. Mitochondria produces the required ATP for the movement of the sperms. Apart from the mitochondria, the neck also has centrioles. Sperm is a haploid gamete and in humans, it contains 23 chromosomes. In male humans, the process of spermatogenesis occurs in the testes and is initiated only at the onset of puberty.

However, once it starts, spermatogenesis is a continuous process that occurs throughout a lifetime unlike oogenesis. Spermatogenesis occurs in the tubular structure called seminiferous tubules.

Spermatogonia, which are immature germ cells, are positioned on the outer edge of the seminiferous tubules near the basal lamina. These germ cells multiply continuously by the process of mitosis. Some of these multiplying cells do not proliferate and are converted to primary spermatocytes.

These primary spermatocytes then undergo the first meiotic phase wherein, each paired homologous chromosomes contribute to cross-over and eventually undergo division I of meiosis resulting in the formation of two secondary spermatocytes, which contain 22 duplicated autosomal chromosomes it can be a duplicated X or a duplicated Y chromosome. These secondary spermatocytes then undergo phase II of meiosis resulting in the formation of haploid spermatids , which further undergoes differentiation to form sperms.

Digestion 2. The Blood System 3. Disease Defences 4. Gas Exchange 5. Homeostasis Higher Level 7: Nucleic Acids 1. DNA Structure 2. Transcription 3. Translation 8: Metabolism 1. Metabolism 2. Cell Respiration 3. Photosynthesis 9: Plant Biology 1. Xylem Transport 2. Phloem Transport 3. As they continue to divide, they eventually form a solid mass of cells, called a morula. This mass of cells is not going to be a full solid sphere but a sphere with distinct layers i. The inner cell mass will differentiate into cells that will later define an embryo.

The trophoblast , in turn, will give rise to cells that will become the structures essential during the uterine wall implantation and the developmental growth of the embryo to the fetus in the uterus. Thus, the zygote not only forms the embryo but it will also be the source of the subsequent outer fetal membranes i.

Because the cells divide fast, with no time to grow, the morula tends to have the same size as the zygote. See the diagram below. From one-celled, it will soon become multicellular, as each cell will undergo mitosis.

This stage is crucial because the dividing cells are more sensitive to the effects of mutagens. Thus, there is a higher risk of genetic errors mutation during this stage.

As a result, women are advised not to take any unprescribed medicine during pregnancy. The cells have innate mechanisms to repair DNA errors, however, they may not be enough when the extent of the damage becomes overwhelming. The fetus is in the final development stage. In humans, the fetal stage begins in the 9th week post-fertilization up to the last week prior to the birth of the baby. This is the period of growth and organ development. In humans, the zygote is the first cell stage of pregnancy.

It is located first in the fallopian tube and moves towards the uterus. As the zygote travels, it divides to give rise to cells that will also undergo mitosis. Soon, the zygote will transition into an embryo that will be implanted in the uterus. There, the embryo will develop further into a fetus. For more info and facts on human development, read the Developmental Biology Tutorials. These tutorials describe how a living thing grows and attains maturity. In many fungi and protists, the fusion of the nuclei of haploid cells produces a diploid zygote, called zygospore.

In fungi, the zygospores are found in the zygosporangia. In algae, the zygospores occur as a cell following the fusion of unicellular gametes. Watch this video below to know the different stages that a human zygote goes through to becoming an embryo.

For human species to obviate extinction, reproductive mature adults should be producing viable offspring in order to continue the existence of the species and pass on genetic information from generation to generation. Read this tutorial to learn more about human reproduction and fertilization Read More.