Mutations 1

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 2

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

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) 4

Types of Mutations 5

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

Five types exist: Chromosome Mutations Deletion Inversion Translocation Nondisjunction Duplication 7

Deletion Due to breakage A piece of a chromosome is lost 8

Chromosome Mutations Cri-du-chat Deletion of material on 5th chromosome Characterized by the cat-like cry made by cri-du-chat babies Varied levels of metal handicaps

Inversion Chromosome segment breaks off Segment flips around backwards Segment reattaches 10

Duplication Occurs when a gene sequence is repeated 11

Translocation Involves two chromosomes that aren’t homologous Part of one chromosome is transferred to another chromosomes 12

Translocation 13

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 14

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Chromosome Mutation Animation 17

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. 18

Types of Gene Mutations Include: Point Mutations Substitutions Insertions Deletions Frameshift 19

Point Mutation Change of a single nucleotide Includes the deletion, insertion, or substitution of ONE nucleotide in a gene 20

Point Mutation Sickle Cell disease is the result of one nucleotide substitution Occurs in the hemoglobin gene 21

Frameshift Mutation Inserting or deleting one or more nucleotides Changes the “reading frame” like changing a sentence Proteins built incorrectly 22

Frameshift Mutation Original: The fat cat ate the wee rat. Frame Shift (“a” added): The fat caa tet hew eer at. 23

Amino Acid Sequence Changed 24

Gene Mutation Animation 25

HOX GENES A series of genes that control the differentiation of cells and tissues in the embryo. Hox genes determine an animal’s basic body plan

POLYDACTYLE

FYI

Normal Male 2n = 46 30 30

Normal Female 2n = 46 31 31

Male, Trisomy 21 (Down’s) 2n = 47 32 32

Female Down’s Syndrome 33 33

Female with Down’s Syndrome

Klinefelter’s Syndrome 35 35

Sex Chromosome Abnormalities Klinefelter’s Syndrome XXY, XXYY, XXXY Male Sterility Small testicles Breast enlargement

XYY SYNDROME

Sex Chromosome Abnormalities XYY Syndrome Normal male traits Often tall and thin Associated with antisocial and behavioral problems

Turner’s Syndrome 2n = 45 39 39

Sex Chromosome Mutations Turner’s Syndrome X0 Female sex organs don't mature at adolescence sterility short stature

Sex Chromosome Mutations XXX Trisomy X Female Little or no visible differences tall stature learning disabilities limited fertility