General characteristics of gene mutations

General characteristics of gene mutations

A genetic mutation is a change in the molecular structure of a genetic material, including changes in codons and cryptographic reading frames in the coding region of the DNA molecule.

Mutations can occur in somatic cells or in germ cells, and these two mutations have completely different consequences. Gene mutations that occur in germ cells can be passed on to future generations. Somatic mutations in genes that occur in other tissue cells of the body can cause morphological or physiological variations in the individual that are mutated and can only be transmitted to offspring through asexual reproduction, but not through sexual reproduction (in embryonic cells) Exceptions occur during developmental periods).

1. The rarity of mutation

The rarity of gene mutations means that under normal conditions, the mutation rate is often very low. The so-called mutation rate refers to the probability that a cell will undergo a certain mutation event under a certain condition in one generation or other specified unit time. In sexual reproduction, the mutation rate is usually expressed by the number of mutant gametes in a certain number of gametes; in the asexually propagated bacteria, the number of mutations in a certain number of bacteria during the splitting process is expressed. It is estimated that the spontaneous mutation rate in higher organisms is generally 1X10-10-1X10-5, that is, one mutation may occur in 100,000 to 10 billion gametes; the spontaneous mutation rate of bacteria is generally 4X10-10-1X10-4 . Under certain conditions, the mutation rates of different organisms and different genes of the same organism are also different.

2. Reversibility of mutation

The mutation is reversible, the wild-type gene is mutated into a mutant gene, and the mutant gene can also be mutated to the original wild-type state. But the mutation frequency of the two is different, and true back mutations are rare. The rate of reversion mutations is always significantly lower than the rate of positive mutations. For example, the positive mutation rate of the wild type (his+) mutation to histidine-deficient (his-) in E. coli is 2X10-6, and the back mutation rate of his-his++ is 4X10-8.

3. Mutational omnidirectionality and multiple alleles

A gene can mutate in different directions. That is, it can be mutated to more than one allele. For example, the A gene can be mutated to the allele α1 α2 α3 .... There can be more than two gene states at a locus, called a multiple allele. Human AB (3 blood type is the complex allele.

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