Thursday, 2 February 2017

Sex Determination in Human Beings notes | Biology notes

Sex Determination in Human Beings

Sex Determination:

  • In human beings we determine the sex with the help of the sex chromosome i.e. with the help of X and Y chromosome.
  • In human beings 46 chromosomes are found out of which 44 are found in 22 pairs called autosomes and other two chromosomes are called sex chromosomes.
  • The rest two chromosomes are same in female and are called X- chromosomes (XX).
  • In male the rest two chromosomes are different and are called X and Y chromosomes.
  • During reproduction females produces one type of gametes and containing 22 autosomes and one X chromosomes, while males produces two types of gametes one have 22 + X type chromosomes and other have 22+ Y types of chromosomes.
  • When a male gametes i.e. sperm carrying X chromosomes fertilizes an ova, the zygote develop into female.
  • When a sperm carrying Y chromosomes fertilizes an egg, zygote develops into male.

Some Genetic Disorder occur due to Chromosomes:

Klinefelter Syndrome:

  • When a male have an extra X or Y chromosome in sex chromosomes then the condition will be XXY or XYY instead of XY. The individual became sterile in this condition.
  • In female when an extra X chromosomes is present instead of XY they show normal development but limited fertility, metal retardness is also seen in this type of syndrome.

Turner’s Syndrome:

  • When female has single sex chromosome(X0) their ovaries are rudimentary, lack of secondary sexual character.

Down’s Syndrome:

When an extra chromosomes is  added to 21st autosomal chromosomes this lead to develop Down’s syndrome.

Colour Blindness:

  • This disorder leads to failure to distinguish between red & green colour.
  •  The gene responsible for this disease is situated on a sex chromosomes.

Patau’s Syndrome:

  • This type of syndrome is developed by an addition of autosomal chromosome in 13th chromosome.
  • There is a cut mark in the lip and person is mentally retarded.
Number of Chromosomes in Different Organisms: