Question

Explain in detail how an individual's sex is determined from fertilization to birth. What determines if a zygote develops in a man or a woman? Explain. When it starts? That determines it at each stage. When does the differentiation end? Who determines it? What structures are developed at each stage? How important are chromosomes and hormones?

Answer 1

Fertilization is the process in sexual reproduction in which a male gamete and female gamete fuse to form a new cell. The sperm and the egg are gametes. They each contain half the genetic information necessary for reproduction. When a sperm cell penetrates and fertilizes an egg, that genetic information combines. The 23 chromosomes from the sperm pair with 23 chromosomes in the egg, forming a 46-chromosome cell called a zygote, so the zygote is formed when the male gamete and female gamete fuse. The single-celled zygote begins to divide into a solid ball of cells. Then, it becomes a hollow ball of cells called a blastocyst..The blastocyst attaches to the wall of the uterus and gradually implants itself into the uterine lining. During implantation, its cells differentiate further.At day 15 after conception, the cells that will form the embryo become an embryonic disc. In this stage the major internal organs and external features begin to emerge, forming an embryo. In this stage, the heart, brain, and spinal cord become visible. Arms and legs start to develop.

Reproductive structures begin to form in the embryonic stage. By week 6, gonads and genitalia are present but undifferentiated. Whether they become male or female is determined by one chromosome delivered by the sperm. the female is XX and the male is XY. Every individual must have at least one X chromosome. Since the female is XX, each of her eggs has a single X chromosome. The male, being XY, can generate two types of sperm: half bear the X chromosome, half the Y. If the egg receives another X chromosome from the sperm, the resulting individual is XX, forms ovaries, and is female; if the egg receives a Y chromosome from the sperm, the individual is XY, forms testes, and is male. All reproductive structures are in place at birth or shortly after. At puberty, an increase in sex hormones will grow them to their adult size and reproductive capability.

Once the formed features of the embryo begin to grow and develop, the organism is considered a fetus. Differentiation and specialization of structures happens during this time.Fetal Development Ends with Labor.