1. Mutations

2. What Are Mutations? Changes in the nucleotide sequence of DNA
May occur in somatic cells (aren’t passed to offspring)
May occur in gametes (eggs & sperm) and be passed to offspring

3. Are Mutations Helpful or Harmful?
Mutations happen regularly
Chemicals & UV radiation cause mutations
Many mutations are repaired by enzymes

4. Are Mutations Helpful or Harmful?
Some type of skin cancers and leukemia result from somatic mutations
Some mutations may improve an organism’s survival (beneficial)

5. Types of Mutations

6. Chromosome Mutations May Involve:
Changing the structure of a chromosome
The loss or gain of part of a chromosome

7. Chromosome Mutations Five types exist: Deletion Inversion
breakage of chromosomes
Deletion
Inversion
Translocation
Duplication
Incorrect number of chromosomes
Nondisjunction
chromosomes don’t separate
properly during meiosis

8. Alterations of Chromosome Structure
A deletion occurs when a chromosome fragment
lacking a centromere is lost during cell division.
This chromosome will be missing certain genes.
A duplication occurs when a fragment
becomes attached as an extra
segment to a sister chromatid.
Images from: Biology; Campbell and Reese; Pearson Education, Inc., publishing as Benjamin Cummings
Slide from: Slide show by Dr. Chuck Downing

9. Alterations of Chromosome Structure
Chromosomal translocations between nonhomologous chromosome are also associated with human disorders.
Chromosomal translocations have been implicated in certain
cancers, including chronic myelogenous leukemia (CML).
CML occurs when a fragment of chromosome 22 switches
places with a small fragment from the tip of
chromosome 9.
Normal chromosome 9
Reciprocal
translocation
Translocated chromosome 9
Philadelphia
chromosome
Normal chromosome 22
Translocated chromosome 22

10. Alterations of Chromosome Structure
An inversion occurs when a chromosomal fragment reattaches to the original chromosome but in the reverse orientation.
In translocation, a chromosomal fragment joins a nonhomologous chromosome.
See a Video
See a Video
Slide from: Slide show by Dr. Chuck Downing
Images from: Biology; Campbell and Reese; Pearson Education, Inc., publishing as Benjamin Cummings

11. Duplications and translocations are typically harmful
Cri du chat
Is a disorder caused by
a deletion in chromosome #5
Mental retardation
Small head
Unusual facial features
“cat cry”

12. PRADER-WILLI Syndrome
Victor Age 1 / Victor Age 2
Born floppy and pale At first refuse to nurse, but later eat until
they become obese
Tiny hands and feet Underdeveloped sex organs
Mildly retarded
Spectacular temper tantrums especially if
refused food
Exceptional proficiency with Jig-saw puzzles
Missing piece of chromosome #15

13. ANGELMAN’S SYNDROME Taut, not floppy Thin Hyperactive Insomniac
Small head
Move jerkily like puppets
Happy disposition
Severely mentally retarded
Rarer than Prader-Willi
Missing SAME piece of Chromosome #15
Colin Farrell’s son has
Angelman’s syndrome

14. Nondisjunction –
Failure of homologous chromosomes OR chromatids to separate at anaphase
Nondisjunction
Normal Meiosis

15. Nondisjunction
Results in ANEUPLOIDY = one or more chromosomes have extra or
missing copies
AFTER FERTILIZATION: Cell with only 1 copy of a chromosome
instead of 2
= MONOSOMY
Cell with 3 copies of a
chromosome instead of 2
= TRISOMY

16. Polyploidy -common among plants
Enduring understanding 3.C: The processing of genetic information is imperfect and is a source of genetic variation.
Essential knowledge 3.C.1: Changes in genotype can result in changes in phenotype c. Errors in mitosis or meiosis can result in changes in phenotype Evidence of student learning is a demonstrated understanding of each of the following: Changes in chromosome number often result in new phenotypes, including sterility caused by triploidy and increased vigor of other polyploids [See also 3.A.2]
Polyploidy -common among plants
Ex: Strawberries = octaploid wheat = hexaploid
Much less common in animals LETHAL in humans
Polyploids are more nearly normal in
phenotype than aneuploids.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

17. POLYPLOIDY Organisms with more than two complete sets of chromosomes
Can occur when a normal gamete fertilizes another gamete in which there has been nondisjunction of all its chromosomes.
Results in triploid (3n) zygote
OR if 2n zygote fails to divide after replicating its chromosomes Results in a tetraploid (4n) embryo
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

18. Down syndrome (Trisomy 21)
Most common chromosomal abnormality (1 in 800 births)
Similar facial features Slanted eyes / Protruding tongue Mild to severe mental retardation
50% have heart defects that need surgery to repair
Both older (35+ years) and younger (under 16 years) mothers are more at risk.

19. Sex chromosomes abnormalities
Human development more tolerant of wrong numbers in sex chromosome
But produces a variety of distinct syndromes in humans
XXY = Klinefelter’s syndrome male
XXX = Trisomy X female
XYY = Jacob’s syndrome male
XO = Turner syndrome female

20. Turner syndrome (X0) 1 in 5000 births
Turner syndrome (X0)
1 in 5000 births
Females have only one X chromosome
Small size
Broad chest
Slightly decreased intelligence
35% have heart abnormalities
Hearing loss common
Reproductive organs don’t develop at puberty

21. Klinefelter syndrome 1 in 2000 births live births
Klinefelter syndrome
1 in 2000 births live births
Males have extra X chromosomes
(Can be XXy, XXXy, or XXXXy)
Taller than average
Normal intelligence have male sex organs, but are sterile. may be feminine characteristics,
Often not discovered until puberty when don’t mature like peers
Presence of BARR BODIES

22. Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2006

23. Karyotype can show: Sex of baby Missing or extra chromosomes
Major deletions or translocations
Can’t see individual gene changes

24. Gene Mutations Change in the nucleotide sequence of a gene
May only involve a single nucleotide
May be due to copying errors, chemicals, viruses, etc.

25. Types of Gene Mutations
Include:
Point Mutations
Substitutions
Insertions
Deletions
Frameshift

26. Point Mutation Change of a single nucleotide
Includes the deletion, insertion, or substitution of ONE nucleotide in a gene

27. Point Mutation
Sickle Cell disease is the result of one nucleotide substitution
Occurs in the hemoglobin gene

28. Frameshift Mutation Inserting or deleting one or more nucleotides
Changes the “reading frame” like changing a sentence
Proteins built incorrectly

29. Frameshift Mutation Original: The fat cat ate the wee rat.
Frame Shift (“t” deleted):
The fat caa tet hew eer at.

30. Amino Acid Sequence Changed