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Mutations 1
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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
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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
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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
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Types of Mutations 5
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Chromosome Mutations May Involve:
Changing the structure of a chromosome The loss or gain of part of a chromosome 6
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Five types exist: Chromosome Mutations Deletion Inversion
Translocation Nondisjunction Duplication 7
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Deletion Due to breakage A piece of a chromosome is lost 8
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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
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Inversion Chromosome segment breaks off Segment flips around backwards
Segment reattaches 10
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Duplication Occurs when a gene sequence is repeated 11
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Translocation Involves two chromosomes that aren’t homologous
Part of one chromosome is transferred to another chromosomes 12
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Translocation 13
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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
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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
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Types of Gene Mutations
Include: Point Mutations Substitutions Insertions Deletions Frameshift 19
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Point Mutation Change of a single nucleotide
Includes the deletion, insertion, or substitution of ONE nucleotide in a gene 20
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Point Mutation Sickle Cell disease is the result of one nucleotide substitution Occurs in the hemoglobin gene 21
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Frameshift Mutation Inserting or deleting one or more nucleotides
Changes the “reading frame” like changing a sentence Proteins built incorrectly 22
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Frameshift Mutation Original: The fat cat ate the wee rat.
Frame Shift (“a” added): The fat caa tet hew eer at. 23
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Amino Acid Sequence Changed
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Gene Mutation Animation
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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
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POLYDACTYLE
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FYI
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Normal Male 2n = 46 30 30
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Normal Female 2n = 46 31 31
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Male, Trisomy 21 (Down’s) 2n = 47 32 32
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Female Down’s Syndrome
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Female with Down’s Syndrome
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Klinefelter’s Syndrome
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Sex Chromosome Abnormalities
Klinefelter’s Syndrome XXY, XXYY, XXXY Male Sterility Small testicles Breast enlargement
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XYY SYNDROME
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Sex Chromosome Abnormalities
XYY Syndrome Normal male traits Often tall and thin Associated with antisocial and behavioral problems
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Turner’s Syndrome 2n = 45 39 39
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Sex Chromosome Mutations
Turner’s Syndrome X0 Female sex organs don't mature at adolescence sterility short stature
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Sex Chromosome Mutations
XXX Trisomy X Female Little or no visible differences tall stature learning disabilities limited fertility
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