Germ Cells Definition:
Germ cells are the cells present in the body, which results in formation of gametes in organism reproducing sexually. The male sperms and female eggs are the precursors, which forms gametes. The germ cells in the organism are the germline.
The germline is distinguished from the body in the embryo development stages. There are two types of cell line, where somatic cell forms the body structures and the germ cells will form gametes and the traits will be passed on to the offspring.
Germs cells can be differentiated from other cells as they divide through meiosis, while other cells divide through mitosis. Germ cells are unipotent as they will form either egg or sperm. Once both the cell type fuses, it results in the formation of totipotent cell, which is a zygote.
Function of Germ Cells:
Germ cells are one of the stem cell type, which results in the formation of gametes. Thus, the sex cells are originated from them and the genetic information is transmitted from parent to the offspring.
As germ cells undergo division by meiosis, it results in maximum variation in gametes and the DNA inheritance is the one which drives evolution and natural selection.
Development of Germ Cells:
The progenitor of germ cells is the primordial germ cells, which are present in the epiblast region of embryo. The primordial germ cells move to the gonads, where they undergo division through meiosis, resulting in the formation of sperm cells or egg.
The daughter cells produced from meiosis are not identical to the parent and contain half the chromosome number and are thus, haploid.
Therefore, the sperm and egg combines resulting in the formation of a diploid zygote, which has DNA from both parents. The genetic information is stored in the germline, where it moves from one generation to other by reproduction.
Germ Cells and Meiotic Division:
Out of all the cell, germ cells are the only cells within the body, which divide by meiosis, resulting in formation of four haploid cells, with single set of chromosome, whereas in mitosis two daughter cells are formed, which resemble the parent and are diploid.
The diploid are the germ cell, which undergo division to form gametes which are haploid, so that the young one has proper number of chromosomes. In meiosis, the chromosome number is reduced to half, but results in genetic variation between species.
Stages of Meiosis in Germ Cells:
There are two stages of meiosis, which are meiosis 1 and meiosis 2. In the cell cycle interphase stage, DNA is replicated before entering the meiosis stage 1. The division in germ cells take place twice, where four haploid gametes are formed.
Prophase 1: In this stage, the germ cell has already duplicated its DNA. The chromosome consist of two identical sister chromatids, which are connected by centromere. The chromosomes condense in this stage and exist as pairs. Spindle fiber formation is also seen. The genetic material is exchanged through crossing over. Thus, the sister chromatids are not identical.
Metaphase 1: The homologous align in the center of the cell, where spindle fibers will attach them to one pair of chromosomes.
Anaphase 1: In this stage, the chromosomes are moved to the opposite poles of the cell, where the sister chromatids are bound to each other.
Telophase 1 and Cytokinesis: The chromosomes are bound together at the end and the cell cytoplasm detaches forming two daughter cells, which are non-identical, haploid and contain half number of chromosomes, then the germ cell.
Prophase 2: The two non-identical haploid cells formed, undergo meiosis 2. The chromosomes again condense and spindle formation occurs.
Metaphase 2: In metaphase 2, chromosomes, align at the center of the cell. sister chromatids are bound to the spindle fibers. Anaphase 2: the sister chromatids moves end apart, as the spindle fiber, pulls them.
Telophase 2 and Cytokinesis: In this stage, two cells form four cells, each having a single chromosome set. Meiosis results in formation of 4 sperm cells, which is called as spermatogenesis, whereas in females, it forms four polar bodies and a single egg cell. and the process is known as oogenesis.
Location of Germ Cells:
Within an organism gonads, germ cells are found. In female, they reside in the ovaries and in males, they are found in testis.