Unit Chunk 2C – Genetic Mutations Day One – Genetic Mutations A genetic mutation is: Any change in DNA, in a gene or a chromosome, and any abnormal change in genetic material. Some mutations are inherited by the next generation, and some are not passed on to offspring. If a mutation occurs in a body cell the mutation will NOT be passed on to the organism’s offspring. If a mutation occurs in the production of a sex cell (gamete), the mutation CAN be passed on to an offspring and affect the offspring’s phenotype (physical traits) and genotype (alleles). EQ: What two principal factors cause genetic mutations? Genetic Mutations are caused by: 1. Changes in the environment OR mutagens: a. ultraviolet radiation b. pollutants and chemicals c. tar from tobacco 2. Errors during DNA replication, transcription, or translation These can be beneficial, harmful or deadly, or not affect organisms in any way. There are two types of genetic mutations: Gene Mutations & Chromosome Mutations Gene Mutations are mutations that affect only one gene or only a few genes on one chromosome. There are two types of gene mutations: Point Mutations & Frameshift Mutations EQ: Define a point mutation, and explain what these gene mutations may cause. Point Mutation – one nucleotide base is replaced by another--a single base is changed at one point on the gene or DNA segment THE FAT CAT ATE THE RAT THE FAT HAT ATE THE RAT Point or Substitution mutations usually affect no more than a single amino acid because only one base on one codon is changed. Point Mutations may cause insignificant phenotype changes, deadly diseases, or may not affect an organism in any way. Whether or not this happens depends on what the point mutation codes for--the same amino acid, a different amino acid, or for no amino acid--a stop codon. The result of a Point Mutation--whether or not an organism is affected by the change on its gene-- is expressed in these mutation terms: * Missense Mutation * Nonsense Mutation * Silent Mutation Day Two – Point Mutations EQ: Define a missense mutation, and describe its effects. Missense Mutation - the substituted base creates a changed codon that codes for a different amino acid, and an altered protein is produced. Diseases caused by missense mutations: Sickle Cell Anemia - blood disease Epidermolysis bullosa - fragile skin disease Liddle syndrome - high blood pressure disease Missense Mutations ARE NOT ALWAYS HARMFUL OR DEADLY! Some of these mutations are insignificant physical changes. EQ: Define a nonsense mutation, and describe its effects. Nonsense Mutation - the substituted base creates a changed codon that codes for a Stop, and ends the amino acid chain too early. This produces a shorter protein that usually does not function properly. Diseases caused by nonsense mutations: Cystic fibrosis - secretory gland disease Duchenne muscular dystrophy - muscle degeneration disease Hurler/Hunter syndrome - damaged organs & physical deformities Nonsense Mutations ARE ALWAYS HARMFUL OR DEADLY! WHY?? EQ: Define a silent mutation, and describe its effects. Silent Mutation - the substituted base creates a changed codon that codes for the same amino acid as the original nucleotide(s), so there is NO change to the protein being produced. theThere are no diseases caused by silent mutations, because the protein made is same one called for in the original codon. Silent mutations have NO effect on the organism—no change occurs. EQ: Define a frameshift mutation, and describe its effects. Frameshift Mutation – The addition or deletion of a nucleotide base that causes a shift in the entire grouping of codons. These mutations shift the reading frame of the genetic code and change the amino acid sequence so that the protein made may not be able to perform its function. Diseases caused by Frameshift mutations: Cystic fibrosis - secretory gland disease Tay-Sachs disease - deterioration of nerve cells and of mental and physical abilities Link to certain cancers and HIV retrovirus Frameshift Mutations ARE ALWAYS HARMFUL OR DEADLY! WHY?? Will a Frameshift mutation ever result in a silent mutation? What kinds of Point mutations will not harm an organism? Day Three – Sex-Linked Genes Gene Mutations That Are Inherited Sex-Linked Genes * The X chromosome and the Y chromosome determine sex. * Genes/alleles located on these chromosomes are called sex-linked genes. * More than 100 sex-linked genetic disorders have now been mapped to the X chromosome, and most of these are point mutations on recessive alleles. * The Y chromosome is much smaller than the X chromosome and so contains less genes. For a recessive trait to be expressed in females, there must be two copies of the allele, one on each of the two X chromosomes. Males have just one X chromosome. Thus, ALL X-linked alleles are expressed in males, the dominant AND the recessive phenotypes! EQ: Explain why sex-linked disorders on recessive alleles are much more common in males than in females. This is why sex-linked genetic disorders on recessive alleles are much more common in males than in females. Males either have the disease (homo rec) or not (homo dom). Males cannot be carriers – they cannot be heterozygous. Males have a 50/50 chance of having the disease. Females must have two recessive alleles to have the disease, and females who don’t have the disease are either Homo dom or they are Heterozygous--carriers of the genetic disorder but do not get the disease. Females have a 1 in 4 chance of having the disease. Hemophilia The X chromosome carries genes that help control blood clotting. A recessive allele in either of these two genes may produce hemophilia. In hemophilia, a protein necessary for normal blood clotting is missing. Hemophiliacs can bleed to death from cuts and may suffer internal bleeding if bruised. Possible inheritance of hemophilia allele: Day Four – Chromosome Mutations & Beneficial Mutations EQ: Define a chromosome mutation. Chromosome Mutations are mutations that change the number and structure of entire chromosomes. These mutations may change the locations of genes on a chromosome or the number of copies of some genes on a chromosome. Chromosomal mutations often give rise to birth defects and congenital conditions that may develop during an individual's lifetime. Most infants born with these mutations do not survive into adulthood. Down Syndrome * Chromosome 21 does not separate correctly. * These babies have 47 chromosomes instead of 46. * Children with Down Syndrome develop slower, may have heart and stomach illnesses and vary greatly in their degree of intelligence. * Down’s syndrome occurs in peoples of all races Cri-du-chat Deletion of material on 5th chromosome Sex Chromosome Abnormalities * XYY Syndrome *Some normal male traits *Often tall and thin *Associated with antisocial and behavioral * XXX Syndrome (Trisomy X) *Some normal female traits *Tall stature *Learning disabilities *Limited fertility Significance of Mutations Most are neutral and do not affect us. *Eye color *Birth marks Some are the cause of genetic disorders that are harmful or deadly. * Sickle Cell Anemia * Down Syndrome * Cancer Some are the cause of genetic changes that are beneficial. * Lactose Tolerance * Immunity to HIV * Evolution and Natural Selection Beneficial Mutations Selective Breeding: Humans take advantage of certain beneficial mutations in plants and animals to breed organisms with these specific traits. Genetic Diversity Evolution and Natural Selection result from mutations that enable populations of organisms to survive from one generation to the next despite changes in ecosystems. EQ: Are beneficial mutations Missense, Nonsense, or Silent mutations? Explain. EQ: If beneficial mutations did not occur, what would probably happen to organism populations? EQ: Why is genetic diversity created by beneficial mutations necessary for life on Earth? EQ: Make and defend a claim based on evidence that inheritable genetic variations may result from: 1) new genetic combinations through meiosis, 2) errors during DNA replication, and/or 3) mutations caused by environmental factors.