Mutations

A. What Are Mutations?

• Changes in the nucleotide sequence of DNA

• May occur in somatic cells – (aka. Body cells) - aren’t passed to offspring

• May occur in gametes- (aka. eggs & sperm) can be passed to offspring

B. Are Mutations Helpful or Harmful?

• Mutations happen regularly • Most mutations are neutral and

have no major impact• Chemicals & UV radiation

cause mutations• Many mutations are repaired

by enzymes

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); mutations influence evolution by natural selection

C. Types of Mutations

1. 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.

Types of Gene Mutations• Include:–Point Mutations–Substitutions–Insertions–Deletions–Frameshift

Point Mutation

• Change of a single nucleotide• Includes the deletion, insertion, or

substitution of ONE nucleotide in a gene

Point Mutation

• Sickle Cell disease is the result of one nucleotide substitution• Occurs in the

hemoglobin gene

Frameshift Mutation

• Inserting or deleting one or more nucleotides

• Changes the “reading frame” like changing a sentence

• Proteins built incorrectly

Frameshift Mutation

• Original:–The fat cat ate the wee rat.

• Frame Shift (“a” added):– The fat caa tet hew eer at.

Amino Acid Sequence Changed

Cystic Fibrosis (CF)

• Monogenic• Cause: deletion of only 3 bases on

chromosome 7• Fluid in lungs, potential respiratory failure• Common among Caucasians…1 in 20 are

carriers– Both parents have to be carriers of the mutated

gene.

Gene Mutation Animation

Chromosome Mutations

• May Involve:–Changing the

structure of a chromosome– The loss or gain

of part of a CHROMOSOME, not a gene

2. Chromosome Mutations

• Five types exist:–Deletion–Inversion–Translocation–Nondisjunction–Duplication

Deletion

• Due to breakage• A piece of a chromosome is

lost

Inversion

• Chromosome segment breaks off

• Segment flips around backwards

• Segment reattaches

Duplication

• Occurs when a gene sequence is repeated

Translocation

• Involves two chromosomes that aren’t homologous

• Part of one chromosome is transferred to another chromosomes

Translocation

Nondisjunction• Failure of chromosomes to separate

during meiosis• Causes gamete to have too many or too

few chromosomes• Disorders:– Down Syndrome – three 21st chromosomes– Turner Syndrome – single X chromosome– Klinefelter’s Syndrome – XXY chromosomes

Chromosome Mutation Animation

Types of Gene Mutations

Original

Deletion

Duplication

Inversion

TranslocationA B H I J

A C D E

A B B C D E

A C B D E

A B C D E

F G C D E

Karyotype – Used to identify gender and chromosomal genetic disorders

Normal Male

282n = 46

Karyotype Song – To the tune of I wish I had an oscar meyer wienner.

• A karyotype is a picture of condensed chromosomes.

• The homologs are paired up and there are 22 autosomes.

• Add in a pair of sex chromosomes and take a careful look.

• If there is one too many or one too short, a nondisjunction happened and a disorder took.

Normal Female

302n = 46

Down’s Syndromeor Trisomy 21

Male, Trisomy 21 (Down’s)

322n = 47

Symptoms of Down Syndrome• Upward slant to eyes.• Small ears that fold over at the top.• Small, flattened nose.• Small mouth, making tongue appear large.• Short neck.• Small hands with short fingers.

Symptoms of Down Syndrome• Low muscle tone.• Single deep crease across center of palm.• Looseness of joints.• Small skin folds at the inner corners of the eyes.• Excessive space between first and second toe.• In addition, down syndrome always involves some

degree of mental retardation, from mild to severe. In most cases, the mental retardation is mild to moderate.

Klinefelter’s Syndrome

362n = 47

Kleinfelter’s syndrome(or Klinefleter’s)

• Disorder occurring due to nondisjunction of the X chromosome.

• The Sperm containing both X and Y combines with an egg containing the X, results in a male child.

• The egg may contribute the extra X chromosome.

XXY

• Males with some development of breast tissue normally seen in females.

• Little body hair is present, and such person are typically tall, have small testes.

• Infertility results from absent sperm.• Evidence of mental retardation may or may not

be present.

• Klinefleter’s

Turner’s Syndrome

402n = 45

Turner’s• Turner syndrome is associated with

underdeveloped ovaries, short stature, webbed, and is only in women.

• Bull neck, and broad chest. Individuals are sterile, and lack expected secondary sexual characteristics.

• Mental retardation typically not evident.

• Chromosomal or monogenic?