distinguish between mutations of chromosomes, including
Useful information
Mutagenesis is the process of producing a mutation.
A mutagen is a physical factor or a chemical substance that causes mutations. Gene mutations are caused by mistakes during DNA replication. The rate of these mistakes occurring is increased due to mutagens. Mutagens include:
Chromosomal mutations occur during meiosis as a result of homologous pairs of chromosomes not separating during the first division. This is called non-disjunction and results in some gametes with extra chromosomes and others with less than the normal number.
Another example of trisomy in humans is Klinefelter’s syndrome (XXY) where the ovum has two x chromosomes and is fertilized by a normal sperm with one Y.
Polyploidy is common in plants such as modern hybrid bread wheat (Triticum aestivum) which has 6N number of chromosomes. In the weed Datura stramonium, the trisomic effect can be detected by the phenotypes of the seed capsule such as rolled, elongate, globe. Many garden flowering plants such as tulips and daffodils are polyploids and they mainly reproduce asexually by bulbs.
Genic mutations occur when the sequence of bases in a section of the DNA molecule is changed. There are two types of genic mutations:
Example
|
Original DNA :
|
CAG TAG GTA |
---|---|---|
Substitute copy :
|
CAG AAG GTA (A has substituted the original T) |
|
Original mRNA :
|
GUC AUC CAU | |
Original amino acids :
|
valine isoleucine histidine | |
Substitute mRNA :
|
GUC UUC CAU | |
Substitute amino acids:
|
valine phenylalanine histidine |