Presentation on theme: "Mutations. What Are Mutations? Changes in the nucleotide sequence of DNA May occur in somatic cells (aren’t passed to offspring, only to descendant cells)"— Presentation transcript:
What Are Mutations? Changes in the nucleotide sequence of DNA May occur in somatic cells (aren’t passed to offspring, only to descendant cells) May occur in germ-line cells (eggs & sperm) and be passed to offspring
Are Mutations Helpful or Harmful? Mutations happen regularly Almost all mutations are neutral Chemicals & UV radiation cause mutations Many mutations are repaired by enzymes
Types of Mutations
Point Mutations Change in the nucleotide sequence of a one or a few base pairs May be due to copying errors, chemicals, viruses, etc.
Types of Point Mutations Include: –Substitutions –Frame-shift Mutations (Insertion, Deletion)
Substitution One or more nucleotides are changed to a different base. AAC GCC AGC AAG GCC AGC Can cause an amino acid to be changed…or not!
Frame-shift Mutation Inserting or deleting one or more nucleotides Changes the “reading frame” like changing a sentence Proteins built incorrectly
Frameshift Mutation Original: –The fat cat ate the wee rat. Frame Shift (“a” added): – The fat caa tet hew eer at.
Amino Acid Sequence Changed
Gene Mutation Animation
How Would the Phenotype Change?
Missense Substitution Sickle Cell disease is the result of one nucleotide substitution Occurs in the hemoglobin gene
Nonsense Substitution Thallasemia is the result of a stop codon substitution that shortens the gene Occurs in the hemoglobin gene
Silent Mutation The Genetic Code is repetitive – there are 64 codons that code for 20 amino acids. A silent mutation makes no change in amino acid sequence:
Deletion Cystic fibrosis (mucus in the lungs) is the result of one nucleotide deletion Causes a frame- shift!
Insertion Huntington’s Disease (nerve cell deterioration) is the result of many nucleotide insertions (CAG repeats)
Chromosome Mutations May Involve: –Changing the structure of a chromosome –The loss or gain of part of a chromosome
Deletion Due to breakage A piece of a chromosome is lost Insertion An additional piece of chromosome is added
Deletion Cri-du-Chat is caused by a deletion in one of the chromosomes. Causes an abnormal larynx
Duplication Occurs when a gene sequence is repeated
Inversion Chromosome segment breaks off Segment flips around backwards Segment reattaches
Translocation Involves two chromosomes that aren’t homologous Part of one chromosome is transferred to another chromosomes
Nondisjunction 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