Mutations are permanent changes in the DNA.
Mutations that produce new alleles:
A forward mutation is a mutation which changes a wild type allele into a new allele.
A true reversion (reverse mutation) is a mutation which changes a mutant allele back into a wild type allele
Mutations that produce a new genes:
1. Gross (chromosome) mutations are changes in chromosome structure.
- Translocations: when two non-homologous chromosomes exchange segments (reciprocal translocation) or when a piece of one chromosome becomes attached to a non-homologous chromosome.
- Inversions: occur when segments of chromosome become reversed.
2.Gene Duplications: occur when a chromosome acquires an extra copy of a chunk of the chromosome.
3. Gene Deficiencies occur when a chromosome loses a portion of its DNA.
4. Frame shifts are created when one or a few bases are inserted or deleted, thus altering the ultimate reading frame of the ribosome.
Reason why some mutations don’t produce changes:
A suppressor mutation causing a reversion and is actually a second change in the same gene, at a different site in the gene, which cancels out the forward mutation of the gene product. Now such gene has two differences when compared to the original wild type, but the protein made following its instructions works just like the original, wild type protein.
In some translocation cases:
An individual who has a balanced translocation carries one set of normal chromosomes and one set of chromosomes which have a translocation. There are no genes missing or damaged, and the genetic function of this individual is unimpaired.
In some inversion cases:
For the individual with teh inversion, there are no necessarily any genetic consequences. As long as there are no missing or damaged genes, the unusual arrangement of DNA is no problem.
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