Genetic mutations, chromosomal and point mutations

1. Mutations all
AP Students
need to know

2. Mutations caused by
whole/part chromosomes

3. Chromosomal mutations
• In nondisjunction, pairs of
homologous chromosomes
do not separate normally
during meiosis
• As a result, one gamete
receives two of the same
type of chromosome, and
another gamete receives
no copy

5.  Having an abnormal number of
chromosomes is a condition known
as aneuploidy
 Having 3 copies of a particular
chromosome is called a trisomy
 Having 1 copy of a particular
chromosome is called a monosomy

6. Polyploidy is a
condition in which
an organism has
more than two
complete sets of
chromosomes
Recent research
has shown that
this Chilean
rodent is a
tetraploid
Very rare among
animals
Common in plants,
some fish, some
amphibians

7.  Polyploidy - having more than two complete
chromosome sets
 The normal state is having 2 of each chromosome
(homologous pairs)
 When organisms have 3 or 4 of each chromosome, that is
called polyploidy
 Triploidy (3n), tetraloidy (4n), hexploid (6n), octapolid (8n)
 Very uncommon in animals
 Some fish and amphibians, mostly
 Quite common in plants

8. Down
Syndrome
 Caused by a trisomy of chromosome 21
 1/700 births in US
 The result of nondisjunction during meiosis I
 Risk increases with the age of the mother
 Mental retardation, increased risk of other diseases, shortened
life span, underdeveloped and likely sterile

9. Trisomy 18 – Edward’s syndrome low birth
weight, mental retardation, extra fingers and toes

10. Trisomy of sex
chromosomes
• Klinefelter
syndrome is the
result of an extra
chromosome in a
male, producing
XXY individuals
• Monosomy X, called
Turner syndrome,
produces X0 females,
who are sterile; it is the
only known viable
monosomy in humans

11. Quick Think
Gene dosage, the number of active
copies of a gene, is important to
proper development.
Identify and describe two disorders
that are the result of improper gene
dosage

12. Alterations of Chromosome Structure
 Chromosomal mutations
include
 Deletion
 Inversion
 Duplication
 Translocation
 Often occur during meiosis
 Chromosomes break &
rejoin incorrectly

13. Deletion mutations
 A piece of
chromosome is
lost during
meiosis
 Cri du chat is
one condition
that results -
distinctive cry,
severe
retardation,
shortened life
span

14. Inversion Mutations
 A double break where
the piece reattaches, but
backwards
 Hemophilia is a inversion
on the X chromosome

15. Duplication mutation
 A piece breaks off
from one
chromosome and
reattaches to the
sister chromatid
 Fragile X syndrome
is caused by this,
2nd most common
form of mental
retardation after
Downs syndrome

16. Translocation mutation
 A piece breaks off one chromosome and
reattaches to a different chromosome
 Burkitt’s lymphoma is caused by this

17. Sex-linked mutations in
humans

18. Colorblindness
 Colorblindness
 Recessive
 X chromosome
 Men are more likely to be colorblind than
women…WHY

19. Hemophilia
 Recessive, X-linked
 Prolonged bleeding when injured
 Clots slow to form
 Caused by a mutation for a gene on
the X chromosome that codes for a blood clotting
protein
 Can be treated but not cured
Bleeding
(bruising) after an
injection

20. Duchenne muscular
dystrophy
 Recessive, X-linked
 1/3500 males in US
 Progressive weakening of
muscles
 Loss of coordination
 Death by early 20s
 Mutation in the gene that codes
for a muscle protein (dystrophin)

21. Point Mutations
Small changes in the DNA
sequence

22. Point Mutations
 point mutation = a change in a
single base pair in a gene
 They can have catastrophic
consequences, or none at all
 3 main types:
Substitution
Insertion
Deletion

23. Substitution mutations
 A base pair is replaced with a different base pair

24. Substitution
 Think of it like a sentence:
 Normal sentence would read
 THE DOG BIT THE CAT
 A point mutation might make the sentence read:
 THE DOG BIT THE CAR
This changes the meaning of the sentence, but not
dramatically.

25. Example: sickle cell anemia

26. Advantages of sickle cell
 AA – no sickle cell, susceptible to the worst effects of
malaria
 Aa – no sickle cell, but call pass recessive allele to
offspring, some protection from malaria
 aa – sickle cell disease
 This is called The Heterozygote Advantage

28.  Changing a single
base may not cause
any change at all:
 The changed base may
still code for the same
amino acid
 Proline is coded for by
CCC, CCA, CCG, and
CCU,
This is called a silent
mutation

29. Insertions & Deletions
•Insertion - add extra letters
•Deletions – delete letters
•called frameshift mutations
• The 3 letter reading frame is
shifted

30. Frameshift Mutations
 Think of it as a sentence again:
 THE DOG BIT THE CAT
 Adding an extra letter makes it:
 THH EDO GBI TTH ECA T
 It changes the entire sentence to nonsense. This
kind of mutation has a more dramatic effect on the
DNA sequence and is usually lethal

31. 1.
2.
3.
 What kind of mutation is represented
by 1, 2, and 3?
 Will mutation 1 affect the resulting
protein?

32. Tay-Sachs
 Frame shift mutation – 4 added nucleotides (insertion)
 Autosomal, recessive

33. Cystic Fibrosis
 Deletion frameshift mutation – 3 missing letters,
autosomal recessive

34. Breast/Ovarian Cancer
 BRCA I and BRCA II – usually a deletion mutation
 Autosomal dominant

35. Huntington’s Disease
 Autosomal dominant
 >37 CAG repeats on the short arm of chromosome 4