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