Biology Tutorials > Genetics and Evolution > Chromosome Mutations

Chromosome Mutations

Mutations at the chromosomal level

It is nature’s intention that the exact genetic information from both parents will be seen in the offspring’s DNA in the critical stages of fertilization. However, it is possible for this genetic information to mutate, which in most cases, can result in fatal or negative consequences in the outcome of the new organism.

Non-Disjunction and Down’s Syndrome

One well-known example of a mutation is non-disjunction. Non-disjunction is when the spindle fibers fail to separate during meiosis, resulting in gametes with one extra chromosome and other gametes lacking a chromosome.

If this non-disjunction occurs in chromosome 21 of a human egg cell, a condition called Down’s syndrome occurs. This is because their cells possess 47 chromosomes as opposed to the normal chromosome complement in humans of 46.

The fundamental structure of a chromosome is subject to mutation, which will most likely occur during crossing over at meiosis. There are a number of ways in which the chromosome structure can change, as indicated below, which will detrimentally change the genotype and phenotype of the organism. However, if the chromosome mutation affects an essential part of DNA, it is possible that the mutation will abort the offspring before it has the chance of being born.

The following indicates types of chromosome mutation where whole genes are moved:

Deletion of a Gene

As the name implies, genes of a chromosome are permanently lost as they become unattached to the centromere and are lost forever

Normal chromosome before mutation
Genes not attached to centromere become loose and lost forever
New chromosome lacks certain genes which may prove fatal depending on how important these genes are

Duplication of Genes

In this mutation, the mutants genes are displayed twice on the same chromosome due to duplication of these genes. This can prove to be an advantageous mutation as no genetic information is lost or altered and new genes are gained

Normal chromosome before mutation
Genes from the homologous chromosome are copied and inserted into the genetic sequence
New chromosome possesses all its initial genes plus a duplicated one, which is usually harmless

The next tutorial continues looking at these chromosome mutations and mutations that happen within genes that can prove to be more harmful to the organism at hand. It also investigates polyploidy in species.