Question

Share your thoughts on the following. Give three instances demonstrating how genes regulate sex determination in mammals.

Answer 1

Answer)....

A developing mammalian embryo's sex determination:

Primary sex determination:

During early embryonic development of mammals mainly at four weeks after fertilization, in humans, 2 groups of cells turn out to be prearranged into the gonad origin those finally develop into either the ovaries or testicles. These gonads will finally be the source of gametes in the adult.

The initial visible indication of sex-specific development, occurring in week-7 in humans, is in males, with the gonads restructuring into two distinct compartments the testicular cords and the interstitial region.

In females, the gonads appear to lack different structures until later in development. Primary sex determination, together with the differentiation of an embryo's gonads, is dependent on genetic factors associated with the embryo's sex chromosomes.

Secondary sex determination:

The hormonal influence on the sex differentiation of other parts of the body, including2 pairs of ducts present in all developing embryos.

the Müllerian ducts and the Wolffian ducts.

Testicles produce Müllerian inhibiting substance, a hormone that causes the Müllerian duct to degenerate. They also produce testosterone, which causes the Wolffian duct to develop into the internal male genitalia, such as the seminal vesicles and the vas deferens. Testosterone also promotes the development of the external male genitalia, including the penis, and it reduces the development of the breasts.

Where in female mammals there are no testicles and thereby no Müllerian factor to inhibit & thereby the Müllerian duct differentiates into internal female genitalia
inhibiting the fallopian tubes, uterus, and cervix.

Gonadotropin-releasing hormone is released from the hypothalamus by GnRH-expressing neurons. The anterior portion of the pituitary gland releases luteinizing hormone and follicle-stimulating hormone , and the gonads produce estrogen and testosterone.

The male, being XY chromosomes, 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.

Sex determining region of the Y chromosome (ion) & Sf1: the link between sry and the male developmental pathway

Protein that may be directly or indirectly activated by SRY is the transcription factor SF1, steroidogenic factor. Sf1, working in collaboration with Sox9, is essential inorder to elevate the levels of AMH (anti-mullerin hormone) transcription. In the Leydig cells or sertoli cells, Sf1 activates the genes encoding the enzymes that make testosterone.

Dax1: a potential ovary-determining gene

This gene, DAX1, has been cloned and shown to encode a member of the nuclear hormone receptor family. Dax1 is expressed in the genital ridges and encode the hormone LH (Leutinising hormone) to stimulate the production of oestrogen in females but in here SRY gene completely suppressed.

Testis-determining factor or sex-determining region Y (SRY) protein, is a DNA-binding protein which is also known as gene-regulatory transcription factor encoded by the SRY gene which enables initiation of male sex determination in humans.