Transcript Mutations
MUTATIONS Biology I Brandon High School What is a Mutation? A mutation is a permanent change in the DNA sequence of a gene. Mutations in a gene's DNA sequence can alter the amino acid sequence of the protein encoded by the gene. There are two main types of mutations: 1. Chromosomal Mutations 2. Gene Mutations TYPES OF MUTATIONS • Gene Mutation • Point Mutation • Frameshift Mutation • Chromosomal Mutation • • • • • Deletion Duplication Inversion Translocation Nondisjunction GENE MUTATIONS • Small scale: one gene is affected • Any change to the DNA sequence of a gene: Nucleotides/Bases may be added, missing, or changed CHROMOSOMAL MUTATIONS • Any change in the structure or number of chromosomes • Large scale: Affect many genes WHAT ARE CHROMOSOMES? • Humans have 23 pairs of chromosomes, with one chromosome from each parent. • The chromosomes are coiled up DNA. • Under normal conditions all of the chromosomes are inherited in tact. POINT MUTATIONS~ THESE AFFECT ONE NUCLEOTIDE, BECAUSE THEY OCCUR AT A SINGLE POINT IN THE DNA SEQUENCE & SUBSTITUTES ONE NUCLEOTIDE FOR ANOTHER. DNA: mRNA: AA: DNA: mRNA: AA: Example TAC GCA TGG AAT AUG CGU ACC UUA Met Arg Thr Leu Substitution TAC GTA TGG AAT AUG CAU ACC UUA Met Hist Thr Leu POINT MUTATION • One base (A, T, C, or G) is substituted for another • Can Cause: Sickle-cell anemia • 3 Possible Consequences: • nonsense mutations: code for a stop, which can translate the protein • missense mutations: code for a different amino acid • silent mutations: code for the same amino acid FRAME SHIFT MUTATIONS~ THESE INCLUDE INSERTING A EXTRA NUCLEOTIDE OR DELETING A NUCLEOTIDE, WHICH SHIFTS THE “READING FRAME” OF THE GENETIC MESSAGE DNA: mRNA: AA: DNA: mRNA: AA: TAC GCA TGG AAT AUG CGU ACC UUA Met Arg Thr Leu Insertion TAT CGC ATG GAA T AUA GCG UAC CUU A Ile Ala Tyr Leu Environmental factors including radiation, chemicals, and viruses, can cause chromosomes to break; if the broken ends do not rejoin in the same pattern, this causes a change in chromosomal structure. DELETION • Deletion – one or more genes are removed. • This is a type of mutation in which an end of a chromosome breaks off or when two simultaneous breaks lead to the loss of a segment. DUPLICATION • Duplication is the copying of a chromosomal segment. INVERSION • Inversion: a segment that has become separated from the chromosome is reinserted at the same place but in reverse order CHROMOSOMAL TRANSLOCATION A chromosomal segment is removed from one chromosome and inserted on another chromosome NONDISJUNCTION • Chromosomes FAIL TO SEPARATE correctly during meiosis NONDISJUNCTION • Produces gametes (and therefore a baby) with one missing chromosome or one extra chromosome NONDISJUNCTION (IN MEIOSIS II) FERTILIZATION NONDISJUNCTION • Every cell in that baby’s body will have __ copies of this chromosome instead of___. • This condition is called ____________. • Trisomy 21 = Individual has _____ copies of chromosome # ________ NONDISJUNCTION • Every cell in that baby’s body will have 3 copies of this chromosome instead of 2. • This condition is called __________. • Trisomy 21 = Individual has _____ copies of chromosome # ________ NONDISJUNCTION • Every cell in that baby’s body will have 3 copies of this chromosome instead of 2. • This condition is called TRISOMY • Trisomy 21 = Individual has __ copies of chromosome # ____. NONDISJUNCTION • Every cell in that baby’s body will have 3 copies of this chromosome instead of 2. • This condition is called TRISOMY • Trisomy 21 = Individual has 3 copies of chromosome # 21. TRISOMY 21 - DOWN SYNDROME KARYOTYPES • A picture of chromosomes in the body. • Chromosomes pairs 1-22 are called autosomes • Chromosome pair 23 are called the sex chromosomes • Due to nondisjunction • Chromosome makeup is XXY • Creates a sterile male KLINEFELTER’S SYNDROME TURNER’S SYNDROME • Due to nondisjunction • Monosomy- the condition in which there is a missing chromosome. • Sex chromosome make up is X only • Females that will not undergo puberty. EDWARD’S SYNDROME • Due to nondisjunction • Extra number 18 chromosome (trisomy 18) • Traits: Low ears, kidney and heart defects PATAU’S SYNDROME • Extra number 13 chromosome (trisomy 13) • Traits: Deformed eyes, ears and lips KEY POINT #1 Too much or too little DNA is bad!