I Relating Mendelism A Physical Basis During Sexual Life Cycles 1875 Mitosis research by cytologist and 1890s Meiosis Chromosome Theory of Inheritance is a basic principle that states genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns B Gene To A Specific Chromosome Thomas Hunt Morgan embryologist from Columbia University says specific genes are on specific chromosomes He did not believe Mendelism or chromosome theory a Choice of Experimental Organism Morgan uses fruit flies to experiment because they breed quickly and produce hundreds at each mating It has only four chromosomes three pair of autosomes and one pair of sex chromosomes 1 Wild Type the normal phenotype for a character of an organism 2 Mutant Phenotype abnormal or mutated phenotype for a character of an organism b Discovery of Sex Linkage Morgan discovered that only male fruit flies possessed white eye meaning that the gene had to be sex linked Since females have two X chromosomes both of them has to have the allele for white eyes for them to acquire that phenotype The trait is recessive 1 Sex Linked Genes genes located on the sex chromosomes C Linked Genes Inherited Together When genes are linked together they generally resemble the phenotypes of the parents and the F1 generation Although major of the phenotypes match those of the parents all possible phenotypes were represented 1 Linked Genes genes that are passed together from parent to offspring as a unit D Genetic Recombinants Definitions The production of offspring with new combinations of traits inherited from two parents a Recombinants of Unlinked Genes There is a 50 frequency of recombinants for genes located on different chromosomes It occurs at metaphase I of meiosis on homologous chromosomes that have unlinked genes Ratio 1 1 1 1 1 Parental Types having the phenotype of the P generation 2 Recombinants new combinations of a specific character b Recombinants of Linked Genes When completely Ratio 1 1 0 0 with only the P generation phenotype E Recombination Data To Map Genetic Loci 1 Genetic Map 2 Linkage Map 3 Map Units 4 Cytological Maps II Sex Chromosomes A Chromosomal Basis of Sex B Sex Linked Genes a Sex Linked Disorders Disorders carried on the X or Y chromosome although majority are carried by the X chromosome The Y chromosome doesn t have a matching gene It is easier for a male to acquire a sex linked disorder because they only have one X chromosome while females have two that have to match in order to have a disorder 1 Color Blindness 2 Duchenne Muscular Dystrophy recessive gene disorder where muscles can t repair themselves because of missing dystrophin 3 Hemophilia recessive gene disorder where there is no factor 8 protein so blood doesn t clot b X Inactivation in Females 1 Barr Body the inactive X chromosome in each cell of a female It is later reactivated in the ovary cells that become ova III Errors and Exceptions A Alterations of Chromosome Number or Structure a Alterations of Chromosome Number 1 Nondisjunction a pair of homologous chromosomes do not separate properly during meiosis I or sister chromatid fail to separate in meiosis II 2 Aneuploidy abnormal chromosome number 3 Trisomic the cell has an extra chromosome 2n 1 4 Monosomic the cell is missing a chromosome 2n 1 5 Polyploidy a cell contains more than one set of homologous pairs 3n or 4n b Alterations of Chromosome Structure 1 Deletion removes a chromosomal segment 2 Duplication repeats a chromosomal segment 3 Inversion reverses a segment within a chromosome 4 Translocation moves a segment from one chromosome to another nonhomologous one c Human Disorders 1 Down Syndrome extra chromosome 21 causing mental retardation and other health problems XXX 2 Turner s Syndrome female doesn t have a second X chromosome so she will not go through puberty XO 3 Klinefelter s Syndrome male has an extra X chromosome so he will be sterile XXY 4 Jacob s Syndrome male has an extra Y chromosome he will be sterile and have mental retardation XYY 5 Triple X female has an extra X chromosome normal health B Phenotypic Effects 1 Genomic Imprinting genes are expressed in a parent of origin meaning depending on the parent the chromosome was retrieved determines the physical expression or disease 2 Fragile X Syndrome abnormal X chromosome the tip is hanging by a thin thread which causes mental retardation in both male and females C Extranuclear Genes 1 Mitochondria and plastids in plants reproduce by replications by the way of extranuclear DNA found in the organs themselves They do not follow the Mendelian inheritance belief because their way of distribution does not follow the same rules The maternal mitochondria is the same in all of its offspring
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