Translocation refers to the movement of material within a plant or the exchange of parts between non-homologous chromosomes. During meiosis, translocations can affect the formation of sex cells, leading to duplicate or missing genes. Translocations can cause diseases such as cancer, infertility, and Down syndrome.
In biology, translocation refers to two completely different processes. In botany, or the study of plants, translocation is the movement of material from one place to another within a plant. In genetics, it is the exchange of parts between two chromosomes. In this article, we will look specifically at chromosomal translocation.
Inside the nucleus of all cells, strands of DNA make up chromosomes, which is where the genes are located. All cells in the body, except the reproductive cells, have matching chromosome pairs or homologous chromosomes. In homologous chromosomes, both chromosomes have the same size and shape and have the same genes in the same location. One of each pair comes from the mother and one from the father. Within the reproductive cells, or sex cells, only one copy of each chromosome occurs.
A translocation is a form of structural change that occurs between non-homologous chromosomes. It often occurs during meiosis when chromosomes are close together. During a translocation, portions of non-homologous chromosomes break off from the original and are then exchanged. The result of a translocation is that the structure of the two chromosomes has now been changed.
Different chromosomes do not carry the same genes in the same location, so different genes are swapped during a translocation. Translocations do not affect the number of genes in the cell as no part of the chromosome is lost. They can affect how genes are expressed by the cell because the sequence of genes has changed. Because a translocation does not cause a loss of genes in a cell, it rarely affects a somatic cell, a nonreproductive cell.
Translocations affect the formation of gametes or sex cells. During meiosis, homologous pairs of chromosomes line up and are separated to form gamete cells with only one copy of each chromosome. If one chromosome in a pair has translocated, it may not be able to pair with its partner due to a change in size or shape. This can effectively block meiosis altogether, which stops the formation of sex cells.
If meiosis goes ahead, the non-homologous chromosomes that have swapped genes will be clumped together only half the time. When they don’t, the gametes that are formed will either have duplicate genes or lack genes. Duplicate and missing genes occur when one incorrect chromosome is segregated with the other chromosome carrying the translocated gene, so there will be two copies of one gene and no copies of the other that was swapped.
If fertilization occurs with one of these gamete types, the resulting zygote may not be viable or may die. If the zygote survives and is missing a copy of a gene, the cell can express harmful recessive genes. With a normal zygote consisting of two normal gamete cells, these recessive genes are usually masked by the dominant ones, so they are not expressed by the organism.
Translocations are most often caused by X-ray-induced damage to chromosomes in the cell. The damage makes the bonds within the chromosomes weaker, thus making them more susceptible to breakage. The breaks lead to many different types of chromosomal mutations, including translocations. Some common human diseases caused by translocations are cancer, infertility and Down syndrome.
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