Role of hormones in serx determination.

• Hormones are known to play a role in sex determination and are sometimes considered as
  environmental factors.
  Poultry breeders have often noticed that a good egg-laying hen starts showing male
  characteristics in old age.
•  Not only does the comb develop on the head, but it crows like a rooster and even starts mating with hens. The explanation came from post mortem anatomical investigations. 
• In poultry females have a single functional ovary. In the centre of this ovary is a small mass of tissue similar to the testis.
•  The female hormones produced by the ovary ensure the normal development and functioning of female characters, at the same time suppressing growth of the small testis-like tissue. 
• If however, due to infection the ovarian tissues are destroyed, the small testicular tissue gets released from inhibition. It grows and produces male hormones due to which the hen starts showing a shift towards maleness.
  It is possible to change sex in poultry under experimental conditions by administering the male hormone testosterone to new born chicks.
•  The normal functioning of ovaries is suppressed and the bird becomes a male. The technique has potential for inducing sex reversal in human beings as well, but so far there is no record of its application. Some cases of natural sex reversal are known in human beings.
• The freemartin cattle is one of the best examples for illustrating the role of hormones in sex determination. When dizygotic twins, consisting of one male and one female are born, it is found that in most cases the female twin shows male characteristics and is sterile.
•  Such a phenotypic male which is genetically female is called a freemartin. The condition originates
  when there is fusion of the two foetal membranes resulting in joining of the blood vessels of the
  male and female twins. 
• The male calf starts producing sex hormones earlier than the female calf. The male sex hormones cross the placenta and reach the female and induce the development of male characteristics. The same thing is known to happen in pigs, goat and sheep.