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  THE FAT CAT ATE THE RAT  TEF ATC ATA TET HER AT H 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  DeletionAC * DEF  DuplicationABBC * DEF  InversionAED * CBF  TranslocationABC * 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 21 st chromosomes  Turner Syndrome – single X chromosome  Klinefelter’s Syndrome – XXY chromosomes

Significance of Mutations Most are neutralMost are neutral Eye colorEye color Birth marksBirth marks Some are harmfulSome are harmful Sickle Cell AnaemiaSickle Cell Anaemia Down SyndromeDown Syndrome cancerscancers Some are beneficialSome are beneficial Sickle Cell Anaemia to MalariaSickle Cell Anaemia to Malaria Immunity to HIVImmunity to HIV You can do some research on the last pointYou 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 5 th 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.