Sex chromatin is a condensed mass of the inactive X chromosome found in the nuclei of female cells. It represents one of the two X chromosomes being inactivated according to Lyon's hypothesis. Lyon's hypothesis states that in females, either the maternal or paternal X chromosome is randomly inactivated in each cell early in development so that only one X chromosome is functional per cell. This process of X chromosome inactivation is called Lyonization.

1. SEX CHROMATIN AND LYON’S
HYPOTHESIS
Presented by
Shrish Chandra Yadav
FGB-05/17
College of Fisheries, CAU
Lembucherra, Agartala

2. SEX CHROMATIN
Material found only in the Nuclei of Female
cells and believed to represent the inactivated
X-chromosome.
A small condensed mass of the inactivated
X-Chromosome which is composed of DNA
and basic Proteins (histones).
These are also called as Barr body.

4.  These are usually located just inside the
Nuclear membrane of the Interphase
nucleus.
 The Number of sex chromatin bodies per
nucleus is one less than the number of X-
chromosome.
 Normal males have none and normal females
have one.
 Normal males and females with Turner
syndrome (XO) have none.

5.  Normal females and males with Klinefelter
syndrome (XXY) have one sex chromatin.
 Super females (XXX) have two sex chromatin.

6. LYON’S HYPOTHESIS
A Hypothesis (by Mary Lyon) stating that only
one of the two X-chromosomes in a female is
functional, the other having become inactive
early in development.
Either the maternal or the paternal
X-chromosome may be inactivated in any
given cell.

7.  Therefore an X-linked trait may be expressed
by some cells and not by others.
 This is mainly the formation of sex
chromatin.
 Process of sex chromatin formation is called
as Lyonization.
 The normal phenomenon that wherever
there are two or more haploid sets of X-
linked genes in each cell all but one of the
genes are inactivated apparently at random
and have no phenotypic expression.

8. LYONIZATION
 The Process by which all X-chromosomes of
the cells in excess of one are inactivated on a
random basis.
Lyonization occurs in men with the Klinefelter
(XXY) karyotype.
X inactivation is Random.
X inactivation is Fixed.
X inactivation occurs early in development.