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Unit: Molecular Genetics

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1 Unit: Molecular Genetics
Lecture #5 Mutations Unit: Molecular Genetics

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 mutations seem to be due a mistake in base pairing during DNA replication. Mutagens- chemical or physical agents in the environment that cause mutations.

4 Examples of chemical mutagens: certain
pesticides, a few natural plant alkaloids, tobacco smoke, and environmental pollutants. Examples of physical mutagens: some forms of electromagnetic radiation, such as X-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 base sequence changes permanently. If a gene in one cell is altered, the alteration can be passed on to every cell that develops from the original one. If the mutation is in a gamete, the alteration will be passed on to every cell in the individual.

6 Effects of Mutations The effects of mutations on genes vary
widely. Mutations may be…. Neutral (have little or no effect on the organism) 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 gene function/ protein function)

7 Beneficial Effects Some 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
4/26/2017 Example of a beneficial mutation - Polyploidy Polyploidy 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
4/26/2017 Most Crop Species are Polyploid Polyploids (like the one on the left) are often larger and stronger than their diploid ancestors (strawberry on right). G. Podgorski, Biol 1010

10 Harmful Effects Some 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 Mutations All mutations fall into two basic groups 1. Gene Mutations - Mutations that produce changes in a single gene 2. Chromosomal Mutations - Mutations that produce changes in whole chromosomes.

13 1. Gene Mutations Point 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.

15 There are different types of Point mutations

16 a. Substitutions In a substitution, one base is changed to a different base. Substitutions usually affect no more than a single amino acid, & sometimes they 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 cat After 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 acid b. Nonsense- code for a stop, which can shorten the protein Silent- 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 point mutations that can occur and the effect those mutations may have on the protein the 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
Deletion This type of mutation involves the loss of all or part of a chromosome.

25 Chromosomes and Inheritance
4/26/2017 A Boy with Cri-du-Chat Syndrome – a Debilitating Disorder Caused by Chromosome Deletion G. Podgorski, Biol 1010

26 Symptoms Cry that is high-pitched and sounds like a cat Downward slant to the eyes Low birth weight and slow growth Low-set or abnormally shaped ears Intellectual disability Partial webbing or fusing of fingers or toes Slow or incomplete development of motor skills Small head (microcephaly), Small jaw (micrognathia) Wide-set eyes Outlook Intellectual 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 5 4/26/2017 G. Podgorski, Biol 1010

28 Duplication This type of mutation produces an extra copy of all or part of a chromosome.

29 3. Inversion This type of mutation reverses the direction of parts of a chromosome.

30 Translocation This type of mutation occurs when part of one chromosome breaks off & attaches to another.

31 Chromosomes and Inheritance
4/26/2017 Translocations Lead to a Number of Human Cancers In Burkitt’s lymphoma, a chromosome translocation causes a cell cycle-promoting gene to always be active. G. Podgorski, Biol 1010

32 Chromosomes and Inheritance
4/26/2017 Aneuploidy 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
4/26/2017 Down Syndrome is Caused by Trisomy for Chromosome 21 Aneuploidy 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? 4/26/2017 Chromosome Non-Disjunction in Meiosis causes Aneuploidy G. Podgorski, Biol 1010

35 Chromosomes and Inheritance
The Frequency of Chromosome Non-Disjunction And Down Syndrome Rises Sharply with Maternal Age 4/26/2017 The phenomenon is clear – the explanation isn’t. G. Podgorski, Biol 1010

36 Chromosomes and Inheritance
4/26/2017 Sex Chromosome Aneuploid Conditions are Common Klinefelter syndrome G. Podgorski, Biol 1010

37 Take 2 minutes to summarize the different types of chromosome mutations that may occur in an individual.

38 Detection/ Diagnosis There 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
4/26/2017 Tests used to search for chromosomal defects in early pregnancy - Amniocentesis and Chorionic Villus Sampling G. Podgorski, Biol 1010

40 Chromosomes and Inheritance
4/26/2017 Pre-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.

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