Source of Genetic Variation & Genetic Disorders

Source of Genetic Variation & Genetic Disorders Mutations

Objectives: Mutations • Identify the primary mechanism for genetic change and differences among organisms. • List the kinds of mutations. • Describe the characteristics of each mutation. • Identify a mutation present in given DNA strands. • Vocabulary • Mutation • Point mutation • Insertion mutation • Deletion mutation • Silent mutation • Missense mutation • Frameshift mutation • Nonsense mutation • Duplication mutation • Inversion mutation • Translocation mutation • Gene rearrangement

The Role of Mutations • Mutation is a fundamental and inevitable aspect of heredity. • Without it we would never see new traits… called genetic diversity. Mutations Cro-magnon  Homo Sapien

Three Outcomes of Mutations…Some Facts… • Can have no impact and may not be detectable. • These have no effect and are lost in the dominant – recessive allele interaction. • Carriers of some mutations don’t know they have them & don’t display as a physical trait. • A very small percentage can be good, or advantageous, and make life easier or better • These are how it’s believed species evolve. • Most mutations that are detected are so because they are deleterious…meaning they result in something bad & many times death. • These are still very low in number.

Mutation: The Basis of Genetic Change • In genetics, a mutation is a change in the structure or amount of the genetic material of an organism. • What is this “genetic material”? = DNA • So: Mutation = change in DNA. • A genetic mutant is an individual whose DNA or chromosomes differ from some original, previous, or normal state.

Mutation: The Source of Genetic Change • Mutation has had a profound affect on life. • For the most part, mutations are the source of GENETIC VARIATION among the same and different species. • Variation is the differences, sometimes subtle, observed between organisms of the same and different species. • Genetic variation is also, technically, the course of genetic issues; disorders and sometimes cancer. • As it is, every unique version of every gene (or every gene for that matter) began as a mutation of some original gene.

Several Kinds of Mutations • DNA and chromosomes are involved in many processes, so there are many kinds of mutations. • Most mutations involve a misplacement of a SINGLE nucleotide in a DNA segment. • A mutation may change the results of a gene (when the gene is translated and transcribed), but not all mutations do so. • Different kinds of mutations are recognized as either changes in DNA or changes in the results of genes.

Several Kinds of Mutations Mutations as Changes in DNA • During DNA replication, the wrong nucleotide may be paired or placed in a sequence. 1. Point mutation: • A point mutation is a change of a single nucleotide in a sequence from one kind of base to another. • POINT: TAC TGC ATG  TAC TGA ATG 2. Insertion or Deletion: • Rarely, mutations can cause the insertion (adding) or deletion (removing) of one or more nucleotides in a sequence. • INSERTION: TAC TGC ATG  TAC ATG CAT G • DELETION: TAC TGC ATG  TAC _GC ATG…

Several Kinds of Mutations Mutations as Changes in Results of Genes • Changes in a DNA sequence may affect the results of genes in many ways. 1. Silent Mutation: • A mutation is silent when it has no effect on a gene’s function because it makes the same amino acid sequence. • SILENT: DNA TAC TGC ATG  TAC TGT ATG • mRNA AUG ACG UAC  AUG ACA UAC • AA met thr tyr  met thr tyr • Point mutations are often silent because the genetic code is redundant • (some amino acids have multiple codons).

Several Kinds of Mutations 2. Missence (Replacement) Mutation: • Results when a codon is changed (bases are switched) such that the new codon codes for a different amino acid. • MISSENCE: DNA TAC TGC ATG  TAC CGC ATG • mRNA AUG ACG CUA  AUG GCG UAC • AA met thr tyr  met ala tyr

Several Kinds of Mutations 3. Nonsense: • Results when an internal codon is changed to a “stop” signal. • In this case, the resulting string of amino acids may be cut short, and the protein may fail to function. NONSENSE : DNA TAC TGC ATG  TAC TGC ATT • mRNA AUG ACG UAC AUG ACG UAA • AA met thr tyr  met thr STOP …

Several Kinds of Mutations 4. Frameshift: • The reading frame of a sequence is the original sequence from the start to the end of the gene. • The reading frame depends on the starting point for reading (the start codon). • This sets up the rest of the gene’s codons. • An insertion or deletion can shift the reading frame, or cause a frameshift. • In frameshift mutations, the remaining sequence may be “read” as different codons. FRAMESHIFT: DNA TAC TGC ATG  TAC ATG CAT G • mRNA AUG ACG UAC AUG UAC GUA C • AA met thr tyr  met tyr val …

Chromosomal Mutations Sometimes mutations result in large scale changes in the arrangement of genes in chromosomes. Chromosomal Mutations • In eukaryotic cells, various affects creates the chance of large-scale mutations in the arrangement and availability of genes at the chromosomal level. • There are 5 main types of chromosomal mutations.

Chromosomal Mutations Chromosomal Mutations • A deletion occurs when a piece of a chromosome is lost. For example: At the end of meiosis, one of the cells will lack the genes from that missing piece. Such deletions are usually harmful. 2. A duplicationoccurs when a piece remains attached to its homologous chromosome after meiosis. One chromosome will then carry both alleles for each of the genes in that piece.

Most proteins can function normally with only one amino acid change. • The more amino acids changed, the more of an affect on the trait. What is the WORST? No affect Little affect • What is the worst? • Remember: Structure determines function • Tough to say as each scenario is unique, however, the more bases changed in the gene will have more of an impact on the amino acids in the trait. Major Affects

Source of Genetic Variation & Genetic Disorders