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Unformatted text preview: XXY males exhibit Klbtefelter syndrome, a condition in which the individual has abnormally small males, is sterile, and is usually of normal intelligence. Males with an extra Y chromosome do not exhibit any well-defined syndrome. Trisomy X results in fe- males who are healthy and distinguishable only by karyotype. Monosomy X individuals Gilli} exhibit Turner syndrome and are phenotypically female. sterile individuals with short stature and usually normal intelligence. Structural alterations oi chromosomes, sudi as dele- tions or iranslocations, maybe associated with specific human disorders. The cri do do: syndrome is caused by a deletion in chromosome 5; cluonic myelogenous leukemiaisacancerthatisassociated wilhareciprccal duomosomal banslocation. I INTERACTIVE UUESTH‘JH 15.3 what I: an explanation for the observation that most as: chromosome aneuploidies have less deleterious effects than do sutosomal aneuploidies? h 155 Some inheritance patterns are Exceptions to the standard chromosome theory Gerramic Benefiting A few dozen traits in mammals havebeenidentified thatseemtodependonwhich parent supplied the alleles for the trait. In this genomic iniprinting, which occurs during gamete formation, certain gerres are imprinted or not, depending on whether ova oraperm are being produced. Imprinted aflelesarenotexpressedintleofispdngi'iihenthis generation makes gametes. old maternal and paternal imprints are removed, and alleles are imprinted accordingtothesexof theparent.Most ofthe mam- malian genes subject to imprinting identified so far are involved in embryonic development. The addition oi methyl groups may inactivate the imprinted gene.r assuring that the developing embryo has only one “five new Inheritance of Organ-relic Genes Exceptions to Mendelian iniieritance are found in the case of extrane— ci‘ear genes located on small circles of DNA in mito- chondria and plant plastids, which are transmitted to oflspringin thecytoplasm oftheovum. Somerarehu- man disorders are caused by mitochondrial mutations, and maternally inherited mitochondrial defects may centribute to diabetes. heart disease. and Alzheimer’s disease. Clmpter 15: The Chromosomal Basis ofl'rtlten‘brrace 115 l-‘l’ord [iris-is aneu- = withth l[enerraticlridyir: a chromosomal aberra- tion in which certain chromosomes are present in extra copies or are deficient in number} cyto- = cell [cytogoisiic mops: diarrs of chromosomes that locate genes with respect to chromosomal fea- hares} hemo- = blood (lieutenants: a human genetic disease caused by a sex-linked recessive allele, characteo ized by excessive bleeding following injury} mono» = one omnwsomic: a chromosomal condition in whichaparticularoellhasonlyonecopyofacluo- mosome, instead of the normal two; the cell is said to be irionosomic for that chromosome} non- - not; dis- = separate {condemns-lion: anaccident ocfmeiosis or mitosis in which both members ofa pair of homologous chromosomes or both sister chromatids fail to move apart properly) poly- = many (polyploidy: a chromosomal alteration in which the organism possesses more than two com- plete chromosome sets] rue-=agairccom =t0gEthEIjb’ln'=tWOalfll'l-IIIEI:N" oonabinsnr: an offspring whose phenotype differs from that of the parents} trans- = across {tmasiocatiam attachment ofa chromo- somal fragment to a nonhomologous chromo- some} iri- = three; aoma- = body [bisoieicr a chromosomal condition in which a particular cell has an extra copy of one chromosome. instead of the normal two; the cell is said to be uisomic for that chromo— am) 5' iriic in re ‘i’n Ll r bin owl oil gs l. Mendel's law of independent assorlment applies tog-cries thatareondifferentcluomosomcs. How- ever, two of the genes Mandel studied were actu- ally located on the same chromosome. Explain why genes located more than 5D map units apart behave as though they are not linked. How can onedetermine whether these genesarelinked and what the relative distance is behveen them? 2. You have found a new mutant phenotype in fruit flies that you suspect is recessive and sexaljniked. 3. Various human disorders or syndromes are related to chromosomal abnormalities. What explanation can you give for the adverse phenotypic efiects as- sociated with these chromosomal alterations? ...
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