Biology I Brandon High School Mutations Biology I Brandon High School

There are two main types of mutations: 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: Chromosomal Mutations Gene Mutations

Types of mutations Gene Mutation Chromosomal 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. This is a normal karyotype of human chromosomes. A karyotype is a picture of chromosomes lined up to look at and compare.

 Point mutations~ these affect one nucleotide, because they occur at a single point in the DNA sequence & substitutes one nucleotide for another. Example DNA: TAC GCA TGG AAT mRNA: AUG CGU ACC UUA AA: Met Arg Thr Leu  Substitution DNA: TAC GTA TGG AAT mRNA: AUG CAU ACC UUA AA: 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

DNA: TAC GCA TGG AAT mRNA: AUG CGU ACC UUA AA: Met Arg Thr Leu  Frame shift mutations~ these include inserting a extra nucleotide or deleting a nucleotide, which shifts the “reading frame” of the genetic message DNA: TAC GCA TGG AAT mRNA: AUG CGU ACC UUA AA: Met Arg Thr Leu  Insertion DNA: TAT CGC ATG GAA T mRNA: AUA GCG UAC CUU A AA: Ile Ala Tyr Leu

Chromosomal M U T A T I O N S  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

Klinefelter’s Syndrome Due to nondisjunction Chromosome makeup is XXY Creates a sterile male

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

Too much or too little DNA is bad! KEY POINT #1 Too much or too little DNA is bad!