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MUTATIONS Changes in DNA that affect genetic information. The ultimate source of variation in individuals. What Causes Mutations? There are two ways in which DNA can become mutated: Mutations can be inherited. Parent to child Mutations can be acquired. Environmental damage due to mutagens Mistakes when DNA is copied What is a mutagen? Mutagens are factors that speed up mutation rate. They include: ionising radiation (x-rays, gamma rays and UV rays). Chemicals such as thalidomide, colchicine, mustard gas, acridine orange. From studies of mutations three main facts emerge: Mutations can arise spontaneously and are in no sense directed by the environment. Mutations are persistent. They tend to be transmitted through many generations without further change. The vast majority of mutations confer disadvantages on the organisms that inherit them. Types of mutation: If the mutation occurs in the body cells (is a somatic mutation it cannot be inherited by offspring). If the mutation occurs in the reproductive cells (gametic cells) and is not lethal, it can be passed on to the offspring and become part of the gene pool. Somatic mutations Occur in somatic (body cells) Affect parts of the body only. Can be passed on by mitosis when cells divide. Can result in different cell lines in one organism eg one brown eye and one blue eye. Some cancers result from somatic mutations. Can be passed on by asexual reproduction eg naval oranges, Royal Gala apples. Not inheritable and only affect organism in their lifetime. Gametic mutations Occur only in gametes (ova, sperm/pollen) These mutations occur during meiosis or in any cells from which sex glands are derived i.e. during embryological development of the sex organs Inheritable Passed on by meiosis and fertilisation If the mutation is survivable and the individual reproduces, the mutation can lead to new alleles in the gene pool. If advantageous it will become more common in the gene pool as a result of natural selection. Gene and chromosome mutations Gene mutations are chemical changes in individual genes. Chromosome mutations involve changes in the gross structure of chromosomes. Gene Mutations Point Mutations – changes in one or a few nucleotides Substitution THE FAT CAT ATE THE RAT THE FAT HAT ATE THE RAT Insertion THE FAT CAT ATE THE RAT THE FAT CAT XLW ATE THE RAT Deletion THE FAT CAT ATE THE RAT THE FAT ATE THE RAT Inversion THE FAT CAT ATE THE RAT THE FAT CAT TEA THE RAT Gene Mutations Frameshift Mutations – shifts the reading frame of the genetic message so that the protein may not be able to perform its function. Insertion THE FAT CAT ATE THE RAT THE FAT HCA TAT ETH ERA T Deletion H THE FAT CAT ATE THE RAT TEF ATC ATA TET HER AT H Disorders caused by gene mutations Sickle cell anaemia You can do some research on this. Chromosome Mutations Changes in number and structure of entire chromosomes Original Chromosome ABC * DEF Deletion AC * DEF Duplication ABBC * DEF Inversion AED * CBF Translocation ABC * JKL GHI * DEF Non disjunction Failure of chromosomes to separate during meiosis Causes gamete to have too many or too few chromosomes Disorders: Down Syndrome – three 21st chromosomes Turner Syndrome – single X chromosome Klinefelter’s Syndrome – XXY chromosomes Significance of Mutations • Most are neutral • Eye color • Birth marks • Some are harmful • Sickle Cell Anaemia • Down Syndrome • cancers • Some are beneficial • Sickle Cell Anaemia to Malaria • Immunity to HIV • You can do some research on the last point Chromosome Mutations Down Syndrome Chromosome 21 does not separate correctly and the child has 3 chromosome number 21. This is called trisomy. They have 47 chromosomes in stead of 46. Children with Down Syndrome develop slower, may have heart and stomach illnesses and vary greatly in their degree of intelligence. Chromosome Mutations Cri-du-chat Deletion of material on 5th chromosome Characterized by the cat-like cry made by cri-du-chat babies Varied levels of mental handicaps Sex Chromosome Abnormalities Klinefelter’s Syndrome XXY, XXYY, XXXY Male Sterility Small testicles Breast enlargement Sex Chromosome Abnormalities XYY Syndrome Normal male traits Often tall and thin Associated with antisocial and behavioral problems Sex Chromosome Mutations Turner’s Syndrome X or XO - absence of one sex chromosome. Foetuses with 22 pairs of autosomes and a Y chromosome never survive to birth Female sex organs don't mature at adolescence sterility short stature Sex Chromosome Mutations XXX Trisomy X Female Little or no visible differences tall stature learning disabilities limited fertility Polyploidy Sometimes cell division fails altogether, resulting in half the gametes having two of each type of chromosome (being diploid instead of haploid) and the rest having none. If a diploid gamete fuses with a normal haploid gamete the resulting individual is triploid. If two diploid gametes fuse the result is tetraploid.