Structural and numerical variations in chromosomes and their implication

3. Topic: Structural and numerical
variations in chromosomes and
their implication

4. TABLE OF CONTENT
Structure of chromosomes
1. Structural Changes (Variations in Chromosome structure):
Deletions
Duplications
Translocations
Inversions
2. Numerical Changes (Variations in Chromosome Number):
a. Trisomy
b.Monosomy
c.polyploidy
d.Tetrasomy

5. What are chromosomes?
• Chromosomes are the structures that hold
genes. These are made up of a long DNA
molecule with part or all of the genetic
material of an organism.

6. 1. Structural Change (Variations in Chromosome structure)
 Any change which alter the basic chromosome structure is known as
structural change.
 Chromosomes are the vehicle of hereditary material or genes. Any
alteration, addition or deletion of chromosomal part leads to alteration
of number, position or sequence of genes in the chromosome.
 These changes are categorized into four classes-
 Deletions
 Duplications
 Translocations
 Inversions

7. Deletions
 A portion of the chromosome is missing or deleted. The chromosome becomes shorter
due to loss of one or more genes.

8. Duplications
 A portion of the chromosome is duplicated, resulting in extra genetic material.

9. Translocations
 A portion of one chromosome is transferred to
another chromosome. There are three main
types of translocation.
 Simple translocation- In simple translocation,
segment from one chromosome will break and
attached to another chromosome.
 Reciprocal translocation- In a reciprocal
translocation, segments from two different
chromosomes have been exchanged.

10.  Robertsonian translocation-
In a Robertsonian
translocation, an entire
chromosome arm has attached
to another at the centromere.
 Loss of chromosomal segment.

11. Inversions
A portion of the chromosome has broken off, turned upside down, and
reattached. As a result, the genetic material is inverted.
Inversion is of two types-
Pericentric inversion- If the inverted segment includes the centromere, the
inversion is called pericentric inversion;
Paracentric inversion- If it does not include centromere the inversion is
called as paracentric inversion.

12. 2. Numerical Changes (Variations in Chromosome Number)
a. Monosomy
b.Trisomy
c.Nullisomy
d.Tetrasomy

13. (i) Monosomy
 They arise by the loss of one chromosome from the diploid set i.e., 2n-l.

14. (ii) Nullisomy
 These arise by the loss of a particular pair of chromosomes i.e.,
2n-2.

15. Trisomy
 These arise by addition of an extra chromosome to the normal diploid set with
the genetic formula, 2n + 1.

16. Tetrasomy
 These arise by the addition of an extra pair of chromosome to the diploid set with a chromosomal
formula 2n + 2.
 By this a particular chromosome is represented in four doses instead of normal two.

17. Numerical Changes produce serious disease
some of them are following.
Down Syndrome (Trisomy 21):
Individuals with an extra copy of chromosome 21 typically
experience intellectual disabilities, distinctive facial
features, and may have associated health issues.

18. Turner Syndrome (Monosomy X):
Females with only one X chromosome
may have short stature, lack of sexual
development at puberty, and potential
infertility.

19. Klinefelter Syndrome (XXY):
Males with an extra X chromosome
may experience infertility, reduced
testosterone, and sometimes learning
disabilities.

20. Implication of chromosomal aberrations in plant breeding and
crop improvement
 Aneuploids have been used to determine the phenotypic effects of loss or gain of different
chromosomes.
 Aneuploids are also used to produce alien addition and alien substitution lines which are
useful in gene transfer from one species to another.
 Aneuploid analysis permits the identification of location of a gene onto a specific
chromosome
 Aneuploids are useful in the identification of chromosomes involved in translocation.
 Chromosome doubling of haploids produces homozygous disomic plants (2n) (double
haploids) in just two years as compared to 6-7 generations required for their production
through selfing.

21.  Triploid sugarbeet produce larger roots and more sugar per unit area than
diploids.
 Autotetraploid varieties of some forage crops like Clove variety Tora, and
Berseem variety Pusa Giant have been released for commercial cultivation.
 Many ornamentals are autotetraploids, they generally have larger flower and
longer flower duration than do doploids.

22. Thank You