Railway Science (Biology-Reproduction in Animals) (Part-III)

Sperm (spermatozoa) is a gamete (sex cell) produced in the male reproductive system. It is a mobile cell with one goal - to fertilize a female egg. Female gametes are produced in the ovary (egg).
Each month, the female produces one egg during her menstrual cycle. Isogamete is a gamete that is similar in shape, and behavior to another gamete with which it can produce a zygote (homogametes). Gametes are reproductive cells of an organism also known as sex cells.

Sexual Reproduction is the combination of reproductive cells from two individuals to form a third unique offspring (fertilization takes place, Gametes are involved and Mixing of hereditary material).

It prepares itself every month to receive fertilized eggs by making its inner lining/endometrium thick. This lining helps in supporting the zygote by providing nutrition. The cervix is the lower end of the womb (uterus).
It is at the top of the vagina that allows fluid to flow in and out of the uterus. Fallopian tubes are bilateral tubes between the ovaries and the uterus in the female pelvis.
They act as channels for oocyte transport and fertilization. The ureters are bilateral thin tubular structures that connect the kidneys to the urinary bladder, transporting urine from the renal pelvis into the bladder.

It helps in maintaining the low temperature of the testes. It is generally 2 − 2.5°C lower than the normal body temperature, which is required for sperm production.
The urinary bladder is a temporary storage reservoir for urine. Ovary, One of a pair of female glands in which the eggs form and the female hormones estrogen and progesterone are made.
The uterus has a muscular outer layer called the myometrium and an inner lining called the endometrium.

Meiosis (Reduction division) is the number of chromosomes in the daughter cell by half. The term Meiosis was given by JB Farmer and Moore in 1905. Meiosis is restricted only to reproductive cells during which a diploid cell divides and gives rise to four haploid cells. Two phases of Meiosis - Meiosis-I (chromosomes are reduced by half) and Meiosis-II (no reduction in chromosomes).

Chromosomes: These are thread-like structures made of protein and a single molecule of DNA that serve to carry the genomic information from cell to cell, passed down from parents. Humans have 23 pairs (total, 46) of chromosomes. Male have 44 autosomes + XY chromosomes.

Cell division is the process by which cells reproduce and multiply. There are two main types of cell division : mitosis (a division of somatic cells (body cells) to produce two identical daughters) and meiosis (the division of reproductive cells (gametes) to produce genetically diverse haploid cells).
Importance of cell division - It is crucial for growth, tissue repair, and the production of gametes. Auxin : It is the hormone that controls the growth of plants.
Gibberellin : It helps in breaking the dormancy of the plant and it also regulates the seeds to sprout. Maleic Hydrazide : It is a herbicide widely used for regulating plant growth.

It takes place in the ovaries. In this process, a diploid oogonium (egg mother cell) increases in size and gets transformed into a diploid primary oocyte. This diploid primary oocyte undergoes the first meiotic division (meiosis I) to form two unequal haploid cells.
The smaller cell is known as the first polar body, while the larger cell is known as the secondary oocyte. This secondary oocyte undergoes a second meiotic division (meiosis II) and gives rise to an ovum.

In women, menarche is the first menstrual period. This timing is influenced by female biology as well as genetic, nutritional and environmental factors. It is a sign of fertility in women.
Menopause refers to the stage in a woman's life when she permanently stops menstruating and is no longer able to conceive naturally.
Adolescence is a transitional period between childhood and adulthood, typically encompassing the ages of 10 to 19 years. Menstruation is the periodic discharge of blood and mucosal tissue from the inner lining of the uterus through the vagina.

Sex chromosomes are the pair which determines the sex in the species. In humans, there are 23 pairs of chromosomes, from which 22 are autosomes and the last one (23rd pair) is the sex chromosome.
It is also known as the X-Y pair. In grasshoppers, males have only one X chromosome besides the autosomes, whereas the female has a pair of X-chromosomes. Males have one X and one Y chromosome (XY) whereas females have two X chromosomes (XX).