2 What is a mutation?Now and then cells make mistakes in copying their own DNA, inserting the wrong base or even skipping a base as a strand is put together.Mutations are heritable changes in genetic information.
3 What causes mutations?Spontaneous Mutations. Some mutationsseem to be due a mistake in base pairingduring DNA replication.Mutagens- chemical or physical agents inthe environment that cause mutations.
4 Examples of chemical mutagens: certain pesticides, a few natural plant alkaloids,tobacco smoke, and environmentalpollutants.Examples of physical mutagens: someforms of electromagnetic radiation, such asX-rays and ultraviolet light.
5 If mutagens interact with DNA, they can produce mutations at high rates.Cells can sometimes repair the damage;but when they cannot, the DNA basesequence changes permanently.If a gene in one cell is altered, thealteration can be passed on to every cellthat develops from the original one.If the mutation is in a gamete, the alterationwill be passed on to every cell in theindividual.
6 Effects of Mutations The effects of mutations on genes vary widely. Mutations may be….Neutral (have little or no effect on theorganism)2. Beneficial (proteins with new or altered functions that can be useful to the organism in a different/ changing environment)Harmful (these mutations may disrupt genefunction/ protein function)
7 Beneficial EffectsSome of the variation produced by mutations can be highly advantageous to an organism or species. Mutations often produce proteins with new or altered functions that can be useful to organisms in different or changing environments. Without mutations, organisms cannot evolve, because mutations are the source of genetic variability in a species.
8 Chromosomes and Inheritance 4/26/2017Example of a beneficial mutation - PolyploidyPolyploidy occurs when all the chromosomes are present in three or more copies.Polyploidy is common in plants and rare in animals.G. Podgorski, Biol 1010
9 Chromosomes and Inheritance 4/26/2017Most Crop Species are PolyploidPolyploids (like the one on the left) are often larger and stronger than their diploid ancestors (strawberry on right).G. Podgorski, Biol 1010
10 Harmful EffectsSome of the most harmful mutations are those that dramatically change protein structure or gene activity. The defective proteins produced by harmful mutations can disrupt normal biological activities, and result in genetic disorders.
11 Take 2 minutes to summarize what mutations are, what causes them, and the effects mutations may have on an organism.
12 Types of MutationsAll mutations fall into two basic groups1. Gene Mutations - Mutations that produce changes in a single gene2. Chromosomal Mutations - Mutations that produce changes in whole chromosomes.
13 1. Gene MutationsPoint mutations - Mutations that involve changes in one or a few nucleotides.They are called ‘point mutations’ because they occur at a single point in the DNA sequence.They generally occur during replication.
14 Sickle cell disease is caused by a point mutation Symptoms of the disease include anemia, severe pain, frequent infections, & stunted growth.
16 a. SubstitutionsIn a substitution, one base is changed to a different base.Substitutions usually affect no morethan a single amino acid, & sometimesthey have no effect at all.
17 Insertion – a point mutation in which one base is inserted into the DNA sequence. c. Deletion- a point mutation in which one base is removed from the DNA sequence.
18 Insertion & Deletion point mutations are also called as ‘Frameshift mutations’ Frameshift mutations - mutations that shift the ‘reading frame’ of the genetic message.Frameshift mutations can change every amino acid that follows the point of the mutation and can alter a protein so much that it is unable to perform its normal functions.
19 Normal: the dog bit the cat Analogy for the effect a frameshift mutation can have on the reading frame.Normal: the dog bit the catAfter an deletion mutation: the dob itt hec at
20 Mutations can also be classified according to their effects on the protein (or mRNA) produced by the gene that is mutated.Missense- code for a different amino acidb. Nonsense- code for a stop, which can shorten the proteinSilent- code for the same amino acid (AA).Sense- mutation changes a stop codon to an amino acid codon, which can lengthen the protein.
22 Take 2 minutes to summarize what you have learned about gene mutations,focusing on the different types of pointmutations that can occur and the effectthose mutations may have on the proteinthe gene codes for.
23 2. Chromosomal Mutations These types of mutations change the number or structure of chromosomes.
24 There are 4 types of chromosomal mutations DeletionThis type of mutationinvolves the loss ofall or part of achromosome.
25 Chromosomes and Inheritance 4/26/2017A Boy with Cri-du-Chat Syndrome – a Debilitating Disorder Caused by Chromosome DeletionG. Podgorski, Biol 1010
26 SymptomsCry that is high-pitched and sounds like a catDownward slant to the eyesLow birth weight and slow growthLow-set or abnormally shaped earsIntellectual disabilityPartial webbing or fusing of fingers or toesSlow or incomplete development of motor skillsSmall head (microcephaly), Small jaw (micrognathia)Wide-set eyesOutlookIntellectual disability is common. Half of children with this syndrome learn enough verbal skills to communicate. The cat-like cry becomes less noticeable over time.
27 Chromosomes and Inheritance Cri-du-Chat is Caused by the Loss of the Short Arm of One Copy of Chromosome 54/26/2017G. Podgorski, Biol 1010
28 DuplicationThis type ofmutation producesan extra copy of allor part of achromosome.
29 3. Inversion This type of mutation reverses the direction of parts of a chromosome.
30 TranslocationThis type ofmutation occurswhen part of onechromosomebreaks off &attaches to another.
31 Chromosomes and Inheritance 4/26/2017Translocations Lead to a Number of Human CancersIn Burkitt’s lymphoma, a chromosome translocation causes a cell cycle-promoting gene to always be active.G. Podgorski, Biol 1010
32 Chromosomes and Inheritance 4/26/2017Aneuploidy occurs when one of the chromosomes is present in an abnormal number of copies.Trisomy and monosomy are two forms of aneuploidy.G. Podgorski, Biol 1010
33 Chromosomes and Inheritance 4/26/2017Down Syndrome is Caused by Trisomy for Chromosome 21Aneuploidy is remarkably common, causing termination of at least 25% of human conceptions.It is also a driving force in cancer progression (virtually all cancer cells are aneuploid).G. Podgorski, Biol 1010
34 Chromosomes and Inheritance What causes aneuploidy?4/26/2017Chromosome Non-Disjunction in Meiosis causes AneuploidyG. Podgorski, Biol 1010
35 Chromosomes and Inheritance The Frequency of Chromosome Non-Disjunction And Down Syndrome Rises Sharply with Maternal Age4/26/2017The phenomenon is clear – the explanation isn’t.G. Podgorski, Biol 1010
36 Chromosomes and Inheritance 4/26/2017Sex Chromosome Aneuploid Conditions are CommonKlinefelter syndromeG. Podgorski, Biol 1010
37 Take 2 minutes to summarize the different types of chromosome mutations that may occur in an individual.
38 Detection/ DiagnosisThere are genetic tests available for many of the human genetic disorders. DNA, RNA, chromosomes or proteins may be analyzed in order to make the diagnosis. Testing may be done for a variety of reasons, such as in order to determine if an individual carries a defective gene that runs in their family. Many genetic disorders can also be diagnosed in early pregnancy.
39 Chromosomes and Inheritance 4/26/2017Tests used to search for chromosomal defects in early pregnancy - Amniocentesis and Chorionic Villus SamplingG. Podgorski, Biol 1010
40 Chromosomes and Inheritance 4/26/2017Pre-Implantation Genetic Diagnosis (PGD)Removing a cell for diagnosis from a human embryo.As a part of in vitro fertilization, this technique may be used to search for chromosome and gene defects prior to implanting the zygote into the women’s uterus.G. Podgorski, Biol 1010
41 Take 2 minutes to summarize how genetic disorders may be diagnosed.