Blueprint of Life Topic 19: Mutations

1. Blueprint of LifeTopic 19: Mutations Biology in Focus, HSC Course Glenda Childrawi, Margaret Robson and Stephanie Hollis

2. DOT POINT(s) • discuss evidence for the mutagenic nature of radiation • explain how mutations in DNA may lead to the generation of new alleles • explainhow an understanding of the source of variation in organisms has provided support for Darwin’s theory of evolution by natural selection

3. Introduction A mutation is a change in the genetic material of a cell— a change in the sequence of nucleotides of DNA. All mutations do not arise in the same manner—some mutations arise spontaneously whereas others are induced. evolution.berkeley.edu

4. Introduction Mutations differ in their effect—some mutations may produce no phenotypic change, whereas others produce little phenotypic effect or significant effect. handmadebymother.blogspot.com

5. Introduction Mutations that are heritable (can be passed on to future generations) are the direct source of all new alleles. christinaa14.wordpress.com

6. Types of Mutations Mutation is a collective term for change in the DNA. The different types of mutation can be distinguished according to three things: 1. the amount of genetic material changed: while most mutations affect only a single gene (gene mutations), there are some mutations that move whole blocks of genes to other parts of a chromosome or to another chromosome entirely. These are called chromosome mutations. pinterest.com

7. Types of Mutations A chromosome mutation is an unpredictable change that occurs in a chromosome. These changes are most often brought on by problems that occur during meiosis (cell division process of gametes) or by mutagens (chemicals, radiation, etc.). ahsmediacenter.pbworks.com

8. Types of Mutations 2. the effect of mutation on phenotype: mutations that do change the phenotype of an individual may be harmful, beneficial or neutral in their effect on the individual and its survival. The phenotypic difference that a mutation produces may be present in the individual only (somatic), or may be transmitted to future generations (gametic). www.mun.ca

9. Types of Mutations Changes in DNA sequences that may occur in somatic body cells are called somatic mutations and can only be passed on to daughter cells within an individual, when the cells carrying the mutation divide by mitosis, e.g. mutations leading to skin cancer in a person. www.rollitup.org

10. Types of Mutations Gametic mutations are those where the mutation occurs in the sexual reproductive cells which give rise to gametes (germ-line cells) and these mutations are heritable— that is, they can be transmitted to future generations, e.g. diseases such as cystic fibrosis (gene mutation) or Down Syndrome (chromosome mutation). pinterest.com

11. Types of Mutations 3. the origin of the mutation: spontaneous mutations arise randomly as a result of an error in a natural process such as DNA replication in cells, whereas induced mutations arise as a result of an environmental agent such as a chemical or radiation that increases the chances of changes to nucleotide sequences. www.livinginstrata.com.au

12. Mutagens Environmental agents that cause mutations are termed mutagens and research has shown that exposure to these substances over a long period of time increases their harmful effects (more so than simply giving a larger dose). www.menshealth.co.uk

13. Mutagens The process of inducing a mutation is termed mutagenesis. There are many mutagens known, including: ■ chemical mutagens: — ingested chemicals: alcohol; tar in tobacco smoke; chemicals in diet—especially charred and fatty foods and food additives and preservatives (e.g. nitrites) — irritants and poisons: organic solvents such as benzene, cleaning products; asbestos, coal tars; pesticides; hair dyes, certain medications www.hackforums.net

14. Mutagens ■ biological mutagens: some viruses and micro-organisms (e.g. hepatitis B virus, HIV, Epstein-Barr virus) directly influence the genetic material in cells, changing the functioning of genes and triggering cancers www.llnl.gov

15. Mutagens ■ mutagenic radiation: — ionising radiation: radioactive materials from nuclear reactions such as radiation from atomic bombs, toxic spills (e.g. that at Chernobyl), radiation used in medicine (e.g. X-rays, gamma radiation) — ultraviolet (UV) radiation: sunlight (and also the UV lights in tanning salons). www.greenbizletter.com

16. Mutagens Today there are strict regulations on the amounts of mutagens that may be present in products or to which people may be exposed. Some chemicals are totally banned and others may be added in very small amounts. Radiation doses are also regulated. www.two-views.com

17. Mutagens The old fashioned idea of consuming things ‘in moderation, not in excess’ may have its merits, since it is the frequency and length of exposure, rather than the amount in each dose, that is harmful. blindgossip.com

18. The Mutagenic Nature of Radiation During the late 1800s and early 1900s, many scientists were involved in studying radiation. Since the harmful effects of radiation were unknown then, scientists, such as Marie Curie, who were exposed to large amounts of radiation over prolonged periods of time developed various illnesses. mariecurietpe.unblog.fr

19. The Mutagenic Nature of Radiation Marie Curie worked with ionising radiation for most of her career and died from leukaemia due to overexposure to radioactive emissions. Many years later survivors of the 1945 bombing of Hiroshima suffered physical mutations as a result of radioactive output from the nuclear explosion. www.biography.com

20. The Mutagenic Nature of Radiation More recently, victims of the nuclear meltdown in Chernobyl in 1986 have suffered high levels of infertility and genetic mutations, as well as non-cancerous side effects such as cardiovascular and respiratory conditions. Do you think there will be any future problems from the recent Japan nuclear meltdown in 2011? pinterest.com

21. Mutations May Lead to New Alleles Mutations alter genes by changing the nucleotide sequence in DNA. As a result one or more genes may be affected. If a gene is altered from its original form the two variations of the gene are termed alleles of that gene. biology.about.com

22. Mutations May Lead to New Alleles These changes to the genes may result in the production of new proteins. Most new proteins have little effect on the organism, but a few will lead to genetic disorders and inherited diseases (e.g. a changed allele for the haemoglobin gene, results in the disease sickle cell anaemia). evolution.berkeley.edu

23. Mutations May Lead to New Alleles Changes to genetic material in somatic cells are not passed on to offspring— the new allele may cause a defect in an individual, but will not affect future generations. However, mutations in germ-line cells (gameticmutations) produce alleles that can be inherited and may therefore have significant effects on populations and so are important in evolution. www.biologyreference.com

24. Gene Mutations On a molecular level, mutations may involve: ■ base substitution (point mutation): one pair of nucleotides (e.g. A-T) is substituted for another pair (e.g. G-C). ■ frame shift (macromutation): extra bases are added to or deleted from a strand of DNA, changing the whole sequence of nucleotides ■ a sequence within a gene may be duplicated or translocated (moved). rosalind.info

25. Chromosomal mutations On a molecular level, if whole chromosomes become rearranged (deleted, duplicated or translocated and attached to another), a change in chromosome number may arise. This usually occurs as a result of chromosomes not separating out correctly during meiosis (that is, non-disjunction). The resulting cells may have one chromosome less than normal or one extra chromosome. www2.pearsonsuccessnet.com

26. Chromosomal mutations The effect of a chromosomal mutation could result in disorders such as Down syndrome, where individuals have three copies of chromosome 21. This has numerous phenotypic effects (e.g. slanting eyes; flat back of the head; short, broad hands; widely spaced toes; growth failure; and mental retardation). noahsdad.com

27. Chromosomal mutations Most gene mutations produce recessive alleles because they prevent the gene from producing a functional protein. Because of this, we could all be carrying large numbers of mutations in our genome and be completely unaware of them. smithlabsafety.wikispaces.com

28. Chromosomal mutations If the changed recessive alleles occur in the homozygous form in individuals (or a dominant allele is present in even one copy) the mutation can affect the phenotype of the individual. This phenotypic change may be of advantage to the organism (e.g. pesticide resistance in an insect), or it may be harmful (e.g. it may cause a disease such as haemophilia). pinterest.com

29. Chromosomal mutations Some phenotypic changes that do not affect the individual adversely (or in a positive way) may accumulate. They may become beneficial or harmful to the organism and affect the overall survival of a population if selective pressure arises as a result of sudden environmental change (e.g. colouration in the peppered moth). www.wired.com

30. Darwin Revisited Mutation is the basic source of all variation. Understanding mutagenesis allows us to explain how variations arise. The understanding that mutations affect the base sequence of DNA allows us to understand how they can be passed from one generation to the next. It supports Darwin’s theory of evolution because it provides a mechanism to explain how heritable variation arises. skepticalteacher.wordpress.com

31. Darwin Revisited A mutation will result in a change in phenotype that may be negligible in its effect, or it may confer some advantage or disadvantage to the organism. Mutations therefore provide the diversity of genetic material that results in variation in phenotype. blog.arkive.org

32. Darwin Revisited If mutations can be inherited, they provide the variation on which natural selection acts, for evolution to occur. For evolutionary purposes, a mutation can be redefined as a heritable change in the genetic material. www.rpdp.net

33. Activity/Homework -Students to read Darwin Revisited article a