Presentation on theme: "Mutations. What Are Mutations? MUTATION = A change in the nucleotide sequence of DNA May occur in somatic cells (aren’t passed to offspring) May occur."— Presentation transcript:
4. Nondisjunction Failure of chromosomes to separate during meiosis Causes gamete to have too many or too few chromosomes Example : Down Syndrome (Trisomy 21) – caused by ___ copies of chromosome 21
Gene Mutations Change in the nucleotide sequence of a gene May only involve a single nucleotide May be due to copying errors, chemicals, viruses, etc.
Types of Gene Mutations Include: Point Mutations Substitutions Frameshift Insertion Deletion
1. Point Mutation Change of a single nucleotide Usually includes the substitution of ONE nucleotide in a gene
Point Mutation Sickle Cell disease is the result of one base substitution Occurs in the hemoglobin gene
Point Mutation (substitution) Original: The fat cat ate the wee rat. Point Mutation (“a” subs for “t”): The fat caa ate the wee rat.
Point Mutation (substitution) The fat caa ate the wee rat. Is the sentence still understandable? Would a point mutation likely cause big problems? What do the simple, three- letter words above represent?
Frameshift Mutation Inserting or deleting one or more nucleotides Changes the “reading frame” like changing a sentence Can cause proteins to be built incorrectly
Frameshift Mutation Original: The fat cat ate the wee rat. Frame Shift (“a” added): The fat caa tat eth ewe era t.
Does it still make sense? If a gene mutation does not change the amino acid, it’s called a SILENT mutation. If a gene mutation changes the amino acid, it’s called a MISSENSE mutation. If a gene mutation changes the amino acid to a “stop” codon, it’s called a NONSENSE mutation.
What is the probability of child V being affected? What is the chance that child V will be a carrier for the disease? If 3 rd generation child Y marries a normal male, what is the probability that they will have 2 child carriers?