Extra credit problem for Lecture 4 An agouti mouse is crossed to a white mouse and all the F1 offspring are agouti An F1 female is crossed to an F1 male and the offspring are 11 agouti 5 white 4 black Q Test the hypothesis that the original parental genotypes were BBCC and bbcc Give the 2 value the df the P value and state whether or not you reject the hypothesis Cytogenetics Chromosome Mutations Aberrations Evolution Chromosomes Prokaryote Eukaryote Eukaryotic chromosomes Human karyotype Why do we care Many diseases and birth defects are a direct result of missing broken or extra chromosomes Down Syndrome Cri du chat Syndrome Patau Syndrome Mutations at the level of the homologous pair EUPLOIDY true ploidy meaning two members of each homologous pair ANEUPLOIDY not true ploidy meaning more or fewer members than two of each homologous pair MONOSOMY one homolog partner is missing TRISOMY three homologs NULLISOMY one entire homologous pair is missing Monosomy and Trisomy Down Syndrome How does it happen Nondisjunction Each chrom has two chromatids Trisomy Patau Syndrome 1 20 000 births severe mental retardation heart and organ defects polydactyly death by the age of one year Chromosomal Abnormalities Occurring in Human Fetuses spontaneously aborted fetuses with the fetuses with the abnormality that Type of Abnormality abnormality survive to term All abnormalities 50 5 Autosomal Trisomies 16 7 5 0 13 18 21 4 5 15 All others 13 8 0 Trisomies of Sex chromosomes XXX XXY XYY 0 3 75 Monosomy for X XO 8 7 1 Structural Abnormalities 20 45 Structural Changes Deletions deficiencies Duplications Inversions Translocations Deletions deficiencies w How can chromosomes break Ionizing radiation production of free radicals which act like little atomic cannon balls blasting through strands of DNA or c somes Chemical insult Why do they rejoin Break points of chromosomes are highly reactive sticky whereas normal ends of c somes are capped by telomeres which do not readily bond to other molecules Breaks that occur will affect both newly formed chromatids all daughter cells arising from them Breaks that occur may affect only one chromatid Thereafter only the progeny carrying the broken chromatid will be affected Cri du chat Syndrome Mental retardation Slow motor skill development Low birth weight and slow growth Small head microcephaly Partial webbing of fingers or toes Wide set eyes hypertelorism High pitched cry Structural Changes Deletions deficiencies Duplications Inversions Translocations Duplication Duplications Bar eye caused by duplication Duplications source of evolutionary novelty Duplication is a source of new genes over evolutionary time e g gene families like globins and MHC genes Structural Changes Deletions deficiencies Duplications Inversions Translocations Inversions
View Full Document
Unlocking...