1) A reciprocal translocation occurs when pieces of two non-homologous chromosomes are exchanged without loss of genetic material. 2) In a translocation heterozygote, the chromosomes involved in the translocation cannot pair normally during meiosis I. Instead, they form a cross-shaped structure called a quadrivalent. 3) The orientation of the quadrivalent at metaphase I determines whether the gametes will receive normal or unbalanced chromosome complements, with adjacent orientations producing non-functional aneuploid gametes and explaining reduced fertility in translocation heterozygotes.

1. Interchromosomal Alterations-
types, effects and detection.
Dr. Lakhvinder Singh
Department of Botany
G.G.M. Science College, Jammu
TRANSLOCATION

2. Chromosomal
Aberrations
Structural Changes
Numerical Changes
Intra-chromosomal Inter-chromosomal
Deletion
Duplication
Inversion
Translocation
Aneuploidy
Euploidy

3. Translocation
• It includes all types of unilateral or
bilateral transfer of chromosome
segments from one chromosome to
another non-homologous
chromosome.
• The genetic significance of
translocation is that genes from one
chromosome are transferred to the
another chromosome.

4. Reciprocal Translocation
•When pieces of two non-
homologous chromosomes
are interchanged without any
net loss of genetic material,
the event is referred to as a
reciprocal translocation.

8. FIGURE (a) & (b): Structure and pairing behavior of a reciprocal translocation between
chromosomes. In (b) pairing occurs during the prophase of meiosis I, after the
chromosomes have been duplicated.
Pachytene
configuration

9. • Figure (a) in last slide shows a reciprocal translocation between
two large autosomes.
• These chromosomes have interchanged pieces of their right
arms.
• If a translocation is present in one of the two sets of
chromosomes, this will be a translocation heterozygote.
• In such plants, normal pairing into bivalents is not possible
among chromosomes involved in translocation.
• Due to pairing between homologous segments of
chromosomes, a cross shaped (+) figure involving four
chromosomes will be observed at pachytene of Meiosis-
I.(Figure b of previous slide).
• This pairing configuration is diagnostic of a translocation
heterozygote.
• Cells in which the translocated chromosomes are in
homozygous condition, they do not form this pattern. Instead,
each of the translocated chromosomes pairs smoothly with its
structurally identical partner.

10. This ring quadrivalent (+) of 4
chromosomes at Pachytene of
meiosis-I can have one of
following three orientations at
Metaphase-I
1.Alternate
2.Adjacent-I
3.Adjacent-II

11. In alternate orientation, alternate
chromosomes will be oriented towards
the same pole)
Anaphase-I
Pachytene
configuration
Quadrivalent

12. In adjacent-I orientation, adjacent chromosomes having
non-homologous centromeres will move towards the same
pole.

13. In adjacent-II orientation, adjacent
chromosomes having homologous centromeres
will move towards the same pole.

14. • Alternate disjunction will give functional gametes.
• Adjacent I and adjacent-II disjunctions will form
gametes which would carry duplications and
deficiencies (aneuploid gametes).
• These aneuploid gametes will be non-functional.
• Therefore, in a plant having translocation in
Heterozygous condition, there will be
considerable pollen sterility.
• The production of aneuploid gametes by adjacent
disjunctions explains why translocation
heterozygotes have reduced fertility.
• Translocation heterozygotes are therefore
characterized by low fertility.

15. References
• Snustard, D.P. and Simmons, M.J. (2012).
Principles of Genetics (6th ed.). John Wiley &
Sons, Inc.
• Klug, W.S.; Cummings, M.R.; Spencer, C.A. and
Palladino, M.A. (2012). Concepts of Genetics
(10th ed). Pearson Education, Inc.
• Karp, G. (2010). Cell and Molecular Biology-
concepts and experiments (6th ed.). John
Wiley & Sons, Inc.

16. Thank You