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Mutations. A Few Words on Mutations. Mutations can be neutral, positive, damaging or lethal Can occur at the single base or chromosomal level Naturally occurring mutations are RANDOM can introduce new traits most mutations are harmful. Causes of Mutations. • radiation • chemical - PowerPoint PPT Presentation
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Mutations
A Few Words on Mutations
• Mutations can be neutral, positive, damaging or lethal
• Can occur at the single base or chromosomal level
• Naturally occurring mutations are RANDOM– can introduce new traits– most mutations are harmful
Causes of Mutations
• radiation• chemical• high temperature• age
Chromosomal Mutations
• Structural– Change in length or arrangement of nucleotides
on chromosomes
• Nondisjunction– Change in chromosome number– Caused by errors in meiosis
Structural Chromosomal Mutations
• Cause birth defects or cancer• Can be one of the following:– Deletions– Duplications– Inversions– Translocations
Deletion
• When part of a chromosome is deleted, usually due to unequal crossing over.
Cri-Du-Chat Syndrome• 1 in 216,000 births
• 46 chromosomes
• #5 Deletion of lower arm
Symptoms:
Moon-shaped face
Heart disease
Mentally retarded
Malformed larynx
Normal lifespan
Duplication
• When part of a chromosome is duplicated, again usually due to unequal crossing over.
Duplication
• Huntington’s– incidence: 1/10,000
in U.S.–nervous system
degenerates
– late onset–may not show
symptoms until past reproductive age
Inversion
• An inversion is a type of mutation where a sequence of nucleotides in the DNA is reversed, or inverted
Translocation
• Mutuation when a there is a rearrangement of parts between nonhomologous chromosomes
Burkitt LymphomaTranslocation of the Myc gene on chromosome 8
Normal Myc genes control cell growth and division•Translocated Myc genes don’t function properly•Leads to cancer of the lymph nodes
Nondisjuction
• Error in meiosis in which chromosomes fail to separate.
• Can happen in Meiosis I or Meiosis II
Changes to Chromosome Number
• Monosomy 2n-1– 45 chromosomes– Turners (XO)
• Trisomy 2n+1– 47 chromosomes– Down syndrome(trisomy 21), Klinefelters (XXY),
Triple X (XXX), Jacobs (XYY)• Polyploidy (Triploid, Tetraploid, etc)
Down Syndrome: Trisomy
Down Syndrome
1 in 1,250 births
47 chromosomesXY or XX
#21 Trisomy Nondisjunction
1 in 31,000 births
46 chromosomesXY=97%
XX=3%
#14/21 Translocation
Down SyndromeShort, broad hands Stubby fingersRough skinImpotency in malesMentally retardedSmall round faceProtruding tongueShort lifespan
Turners Syndrome1 in 5,000 births
45 chromosomes X only
#23 MonosomyNondisjunction
96-98% do not survive to birthNo menstruationNo breast developmentNarrow hipsBroad shoulders and neck
Klinefelter Syndrome1 in 1,100 births
47 chromosomesXXY only
#23 Trisomy Nondisjunction
Scarce beard
Longer fingers and arms
Sterile
Delicate skin
Low mental ability
Normal lifespan