Variation of organisms occurs from linkages and crossing over. The Independent Assortment of Random Fusion of gametes also creates variation. Mutation will occur and new gametes or alter existing ones. What is mutation?
Mutation is a permanent alteration of a genomic sequence. It may be divided into two categories: 1) Point/ Gene Mutation
2) Chromosomal Mutation
Mutations may either be advantageous or disadvantageous and are not all inherently negative
Point/ Gene Mutation
They occur at a single locus on a chromosome. It results in a change to the nucleotides on DNA molecules whether they are replaced, shifted or a new one/set is added. Gene mutations may be divided into the following categories: 1) Duplication
Duplication: when a portion of a nucleotide becomes repeated Addition: an extra nucleotide sequence becomes inserted in the chain Deletion: a portion of the nucleotide in the chains is deleted Inversion: A nucleotide sequence in the chain becomes separated from the chain then regions in its original position only inverted. The nucleotide sequence of this portion is therefore reversed. Substitution: one of the nucleotide is replaced by another which has a different organic base.
Change in the DNA nucleotide sequence for sickle cell is in substitution mutation. The replacement of a single base in the DNA molecule results in the production of the wrong amino acids being incorporated into two of the polypeptide chains which make up the haemoglobin molecule.
Val – His – Leu – Thr – Pro – Glu – Glu
Val – His – Leu – Thr – Pro – Val – Glu
Chromosomal mutation takes place when the number of chromosomes changes or when structural changes occur in the chromosome. This process occurs generally during the formation of a zygote where changes in the number...
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