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  Section: Genetics » Structural Changes in Chromosomes
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Structural Changes in Chromosomes

Structural Changes in Chromosomes
Variations in the structure and number of chromosomes have been observed in natural populations and could also be produced artificially in a variety of organisms. These variations have been extensively studied and can be due to either structural changes or numerical changes. this section will be devoted to structural changes in chromosomes, and the next main topic will deal with numerical changes.

Structural changes can be of following types : (i) deficiency which involves loss of a part of chromosome, (ii) duplication, which involves addition of a part of chromosome, (iii) inversion, which involves a reverse order of the genes in a part of chromosome, and (iv) translocation, which involves exchange of segments between non-homologous chromosomes.

These structural changes are diagrammatically represented in Figure 19.1, where two non-homologous chromosomes from the complete set are shown. Structural abnormalities may be found in both the homologous chromosomes of a pair, or in only one of them. When both homologous chromosomes are involved, these are called structural homozygotes e.g., deficiency homozygote, duplication homozygote, etc. If only one chromosome is involved, this will be called a structural heterozygote. The constitutions of a translocation heterozygote and that of a translocation homozygote are shown in Figure 19.2. In this section, a brief and elementary account of different structural changes is presented.

Different kinds of changes in chromosome structure.
Fig. 19.1. Different kinds of changes in chromosome structure.
Chromosome constitution of a translocation heterozygote and a translocation homozygote.
Fig. 19.2. Chromosome constitution of a translocation heterozygote and a translocation homozygote.


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