MUTATIONS Chapter 12: pages 345 – 349

Mutation Goals Explain the difference between chromosomal and gene mutations 2

Mutations MUTATION: an inheritable change in genetic information. Can be spontaneous or caused by x-rays, ultraviolet light, or radioactive substances. Gene mutations: any chemical change that affects the DNA molecule 3

Gene Mutations Point Mutation – involves a single nucleotide; such as the substitution of one nucleotide for another. Can change one amino acid for which the gene codes Sickle Cell Anemia 4

Gene Mutations Frameshift Mutations – when a nucleotide is inserted or deleted resulting in the grouping of nucleotides being shifted. Can cause tremendous changes to a polypeptide chain. Mutation Repair 5

Gene Mutations 6

Chromosomal Mutations involve a change in the structure of a chromosome normal chromosome one segment repeated three repeats

Duplication Gene sequence that is repeated several to hundreds of times Duplications occur in normal chromosomes May have adaptive advantage Useful mutations may occur

Deletion Loss of some segment of a chromosome Most are lethal or cause serious disorder

Deletion Cru-Du-Chat Cru-Da-Chat Cry

Inversion A linear stretch of DNA is reversed within the chromosome segments G, H, I become inverted

Translocation A piece of one chromosome becomes attached to another nonhomologous chromosome Philadelphia chromosome arose from a reciprocal translocation between chromosomes 9 and 22

Translocation one chromosome a nonhomologous chromosome nonreciprocal translocation

Chromosomal Mutations 14

Chromosomal Mutations Non-disjunction occurs when chromosomes fail to separate properly during meiosis. missing chromosomes (Monosomy) too many chromosomes (Polyploidy). Usually fatal in animals and therefore humans, although some like trisomy 21, are not fatal, but result in serious abnormalities. Can result in hardier varieties in plants. 15

alignments at metaphase II nondisjunction at anaphase I gametes anaphase II alignments at metaphase II nondisjunction at anaphase I chromosome alignments at metaphase I

Autosomal Nondisjunction

Downs Syndrome

Patau Syndrome Trisomy 13 Serious eye, brain, circulatory defects as well as cleft palate 1:5000 live births

Edwards Syndrome Trisomy 18 Every organ is affected 1:10,000 births Life expectancy few months (full trisomy 18)

Sex Nondisjunction

Sex Nondisjunction Turner Syndrome Inheritance of only one X (XO) 98% spontaneously aborted Survivors are short, infertile females No functional ovaries Secondary sexual traits reduced May be treated with hormones, surgery

Sex Nondisjunction

Sex Nondisjunction Klinefelter Syndrome XXY condition Results mainly from nondisjunction in mother (67%) Phenotype is tall males Sterile or nearly so Feminized traits (sparse facial hair, somewhat enlarged breasts) Treated with testosterone injections

Sex Nondisjunction

Sex Nondisjunction XYY Condition Taller than average males Most otherwise phenotypically normal Some mentally impaired Once thought to be predisposed to criminal behavior, but studies now discredit