This theory proposes that hereditary traits are transmitted from one generation to the next through chromosomes and gametes. Gametes contain only one set of chromosomes and fuse during fertilization to restore the paired chromosome condition. Chromosomes are replicated and passed from parents to offspring, behaving in accordance with Mendel's laws of inheritance and explaining the mechanism of inheritance. Sex is determined by sex chromosomes, which can be of the XX-XY, ZZ-ZW, or XX-XO types.

1. CHROMOSOMAL THEORY OF
INHERITANCE
Dr. N. Yuvaraj
Assistant Professor
Achariya Arts and Science College
Villianur- 605110
yuvaraj.aasc@achariya.org

2. This theory was proposed by Walter Sutton and Theodor
Boveri (1902).

3. The two workers found a close similarity between the
transmission of hereditary characters and behaviour of
chromosomes while passing from the one generation to the
next through agency of gametes.

4.  Gametes serve as the bridge between two successive generations.
 Male and Female gametes play an equal role in contributing hereditary
components of future generation.
 Only the nucleus of sperm combines with ovum. Thus, the hereditary
information is contained in the nucleus.
 Chromatin in the nucleus is associated with the cell division in the form
of chromosomes.
Female gamete
Male gamete

5.  Any type of deletion or addition in the chromosomes can
cause structural and functional changes in living beings.
 Determination of sex in most of the animals and plants is
affected by specific chromosomes. These chromosomes
are called sex chromosomes.

6. Salient features of chromosome
theory

7. 1. Both chromosomes as well as genes occur in
pairs in the somatic or diploid cells.
Male Female

8. 2. A gamete contains only one chromosome of a
type and only one of the two alleles of a
character.
Male gamete
Female gamete

9. 3. The paired condition of both chromosomes as well as
Mendelian factors is restored during fertilization.

10.  Chromosomes are also transferred from one generation to the next
as in the case of genes (Mendelian factors).
 The number of chromosomes is fixed in each living species. These
are found as homologous pairs in diploid cells.
 One chromosome from father and the other contributed by the

11.  Before cell division, each chromosome as a whole and the
alleles of genes get replicated and are separated during
mitotic division.
 Meiosis takes place during gamete formation.
 Homologous chromosomes form synapses during
prophase-I stage which in later course get separated and
transferred to daughter cells.
 Each gamete or a haploid cell has only one allele of each
gene present in the chromosome.

12. • A characteristic diploid number is again established by
the union of the two haploid gametes.
• Both chromosomes and the alleles (Mendelian factors)
behave in accordance to Mendel's law of segregation.

13. Linkage and Recombination
 Linkage is the phenomenon, where two or more linked genes are
always inherited together and their recombination frequency in a test
cross progeny is less than 50%.
 A pair of genes may be identified as linked, if their recombination
frequency in a test cross progeny is lower than 50 percent.
 All the genes present on one chromosome form a linkage group and
an organism possesses as many linkage groups as its haploid number
of chromosomes.
 If the two genes are fully linked, their recombination frequency will
be 0%.

14. Sex Determination by chromosomes
Those chromosomes which are involved in the determination of sex of an
individual are called sex chromosomes while the other chromosomes are
called autosomes.
1) XX – XY type:
2) ZZ – ZW type:
3) XX – XO type:

15. Sex determination in Humans
 Human beings have 22 pairs of autosomes and one pair of sex
chromosomes.
 All the ova formed by female are similar in their chromosome
type (22+X).
 Therefore, females are homogametic.
 The male gametes or sperms produced by human males are of two
types, (22+X) and (22+Y).
 Human males are therefore, heterogametic.
 The two sexes produced in the progeny is 50:50 ratio.