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Human Biology
Stephen Wright

LECTURE MARCH 22, 2011 Changes in chromosome number leading to alterations in phenotype Gene mutations are sources of change, diff genotypes Genome can be remodelled by large scale chromosomal changes o Many genes affected simultaneously o Detected by molecular and genetic analysis, microscopy EX. Downs syndrome Plant breeders often manipulate chromosome number to improve or enhance crops Euploidy organisms or cells that have complete set of chromosomes Diploid individuals humans have 2 sets of chromosomes normally If an individual lacks entire set of chromosomes If one entire set is missing, monoploidy results Polyploidy occurs in an individual that has more than normal number set of chromosomes o Triploid 3 sets o Tetraploid 4 sets o Notation is N o These are all euploidy Aneuploidy refers to changes in part of chromosome set, not entire set In other words, loss or gain of one or more chromosomes Monosomy when one specific chromosome is missing Trisomy causes Downs syndrome o Gain one extra chromosome Tetrasomy gain two extra specific chromosomes Differs from wildtype by PART OF CHROMOSOME SET Monoploids are different from haploids Normally haploid has one chromosome set wildtype is haploid in this case Monoploid arises due to aberrant euploidy Monoploidy Males of bees, wasps, etc. are monoploid o Develop by parthenogenesis o Single set of chromosomes bypass meiosis, producing gametes by mitosis Usually lethal in other systems and species o Unmask recessive lethals o Genetic lode individuals will have wildtype copy that will mask the recessive lethal allele Monoploidy cases recessive lethal are now unmasked So mutant phenotypes expressed
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