Duplications typically arise from an event termed unequal crossing-over (recombination) that occurs between misaligned homologous chromosomes during meiosis (germ cell formation). The chance of this event happening is a function of the degree of sharing of repetitive elements between two chromosomes.
What causes a chromosomal duplication to occur?
When the condition occurs sporadically, it is caused by a random error during the formation of the egg or sperm cell , or during the early days after fertilization. The duplication occurs when part of chromosome 1 is copied (duplicated) abnormally, resulting in the extra genetic material from the duplicated segment.
How does a duplication mutation occur?
A type of mutation in which a portion of a genetic material or a chromosome is duplicated or replicated, resulting in multiple copies of that region. Duplication results from an unequal crossing-over between misaligned homologous chromosomes during meiosis.
How do chromosomal deletions occur?
Chromosomal deletions occur spontaneously at a low frequency, or are induced by treatment of germ cells (most efficiently, mature or maturing oocytes in the female, and postmeiotic spermatogenic cells in the male) with chromosome-breaking agents, such as acute radiation or certain chemicals.
What is an example of duplication?
If a deletion is a missing ingredient in the recipe, a duplication is an extra ingredient. One example of a rare genetic disorder of duplication is called Pallister Killian syndrome, where part of the #12 chromosome is duplicated.
Is gene duplication good or bad?
Duplicate genes are not only redundant, but they can be bad for cells. Most duplicate genes accumulate mutations at high rates, which increases the chance that the extra gene copies will become inactive and lost over time due to natural selection.
Are chromosomal deletions inherited?
Although it is possible to inherit some types of chromosomal abnormalities, most chromosomal disorders (such as Down syndrome and Turner syndrome) are not passed from one generation to the next.
Which disorder is the result of a chromosomal abnormality?
For example, an extra copy of chromosome 21 causes Down syndrome (trisomy 21). Chromosomal abnormalities can also cause miscarriage, disease, or problems in growth or development. The most common type of chromosomal abnormality is known as aneuploidy, an abnormal chromosome number due to an extra or missing chromosome.