Germ Cell vs. Somatic Cell Mutations Germ Cell vs. Somatic Cell

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

Point Mutations cont. 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.

Point Mutations

Chromosomal Mutations 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 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

Down's Syndrome 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

Klinefelter's Syndrome Trisomy of sex chromosomes; XXy male Feminine Characteristics, Infertile George Washington? No Children – Sterile? Dental Problems Height – Very tall for generation Still Inconclusive

Turner's Syndrome Monosomy of Sex Chromosomes; XO female Infertile Dwarfism Overweight Some mental retardation Webbed Neck

Edward's Syndrome 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

Edward's Syndrome

Patau's Syndrome Trisomy 13 Cleft Lip and Palate Polydactyl – more than ten fingers/toes 1/6000 births Most die within first year

Cri-du-chat “Cat’s Cry” Syndrome Deletion of a portion of Chromosome 5 Mental Retardation

Causes of Mutations 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.