Mutations

Germ Cell vs. Somatic Cell

Gene Mutation: affects either one nucleotide or one codon

Substitution: one nucleotide is replaced with a different nucleotide resulting in a new codon If the new codon codes for same amino acid – no

effect is show. (Silent Mutation)

If the new codon codes for a different amino acid or stop codon. (causing mis-sense or non-sense mutations)

Ex: Sickle Cell Anemia Substitution: Adenine replaced by Thymine in a single codon;

results in a defective form of hemoglobin

Point mutations are small (but significant) changes.often in a single nucleotide base.

Frame-shift Mutation: caused by additions and deletions of one nucleotide; all codons after mutation are grouped incorrectly Mutation at beginning of gene is worse than near the end of

gene

Frame shift mutations result from either addition or deletion of one or two nucleotide bases. When this occurs the "reading frame" is changed so that all the codons read after the mutation are incorrect, even though the bases themselves may be still present.

Germ-Cell: occurs in gametes; only affect offspring

Somatic Cell: affects body cells; only affects organism

Lethal: causes death; often before birth (miscarriages)

Chromosome: changes to part or the whole chromosome; cannot be repaired by enzymes

Deletion: loss of a piece or whole chromosome Inversion: segment of chromosome breaks off

and reattaches in the reverse order on same chromosome

Translocation: piece of chromosome breaks off and reattaches to a nonhomologous chromosome

Down’s Syndrome: Trisomy 21; 3rd 21 can translocate to chromosome 13 (young mothers)

Duplication: part of chromosome attaches to homologous chromosome giving two copies of gene on that chromosome

Nondisjunction: failure of a chromosome to separate from its homologous chromosome during anaphase of meiosis; one gamete receives extra copy of chromosome other gamete does not receive one

Karyotype: chromosomes are stained and photographed under the microscope, cut from photo and arranged by size and shape; can detect chromosomal abnormalities

Monosomy: a zygote with only 45 chromosomes; one copy of a chromosome

Trisomy: three copies of a chromosome; 47 chromosomes total Both result from

nondisjunction

Trisomy 21 Mild to severe mental

retardation Distinct Facial Features Heart Defects Fingerprints – Sworl Most Common Birth

Defect – 1/700 births Mother’s Age over 40 –

1/80 Problems during

Oogenesis

Trisomy of sex chromosomes; XXy male

Feminine Characteristics, Infertile

George Washington? No Children – Sterile? Dental Problems Height – Very tall for

generation Still Inconclusive

Monosomy of Sex Chromosomes; XO female

Infertile Dwarfism Overweight Some mental

retardation Webbed Neck

Trisomy 18 Elfin Appearance Low set ears Malformation of many

organs – specifically heart/lungs “Blue Babies” due to

lack of oxygen

90% die within first 6 months

Trisomy 13 Cleft Lip and

Palate Polydactyl – more

than ten fingers/toes

1/6000 births Most die within

first year

“Cat’s Cry” Syndrome

Deletion of a portion of Chromosome 5

Mental Retardation

• Spontaneous Mutations – Occur naturally within a cell, although at a normally low rate.

• Induced Mutations – caused by a mutagen introduced into the cell.

• Include:• Physical - agents that forcibly break nucleotide

sequences and cause changes to one or both strands of a DNA molecule.

• Chemical – molecules that enter a cell and induce permanent changes in the DNA.