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.