mutations

Genes and alleles (mutations)  Define mutation. It is any accidental change in the DNA sequence of nucleotide of a gene which is inherited by the next generation.  What is a wild allele? It is the initial allele common in a population.  How are alleles formed? Different alleles are formed by mutations of the wild allele. Mutations  Are mutations transmitted from one generation to another? Mutations in a germline cell (gametes) can be transmitted to offsprings. In contrast, mutations that occur only in somatic cells are not transmitted to offsprings. Transmitted by meiosis sperm during fertilization zygote mitosis body cells Chromosomal mutations In Number: - Extra chromosome (trisomy - Missing chromosome (monosomy In Structure: - Part of the chromosome is deleted so many genes may be deleted - Gene mutations - Substitution, deletion or insertion of nucleotide Mutation in Germ cell in testicle 2 Transmitted by meiosis ovum during fertilization zygote mitosis body cells All body cells originate from a zygote. All cells of the organism have same mutations in the same gene because genetic information is conserved during mitosis. Types of gene mutations Point mutation by substitution It occurs when one nucleotide of a codon is replaced by another. Point mutation by Substitution  Whereby one nucleotide of a codon is replaced by another. Deletion  Whereby one nucleotide is deleted. Insertion  Whereby one nucleotide is inserted Mutation in Germ cell in ovary 3 Mutation by deletion It occurs when one nucleotide is deleted. Mutation by insertion It occurs when one nucleotide is inserted Effects of gene mutations Substitution 1. Missense: Change in 1 amino acid at the site of mutation. 2. Silent: no change in the sequence of amino acid. Same phenotype 3. Nonsense: when the mutation results in a Stop codon. Part of the protein is synthesized. (shorter peptide) Deletion Frame shift from the site of mutation till the end. Approximately no change in the size of protein molecule Insertion Frame shift from the site of mutation till the end. Approximately no change in the size of protein molecule 4 5 Mutation in DNA sequence abnormal protein new phenotype (disease) Very Important note: When a point mutation by substitution occurs and the effect is silent, the phenotype will not change. Substitution mutation having silent effect same protein same phenotype (no change)