mutations. a few words on mutations mutations can be neutral, positive, damaging or lethal can occur...
Post on 25-Dec-2015
221 Views
Preview:
TRANSCRIPT
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 Lymphoma
Translocation 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
top related