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AnnouncementsSex Chromosomes and Sex DeterminationPowerPoint PresentationSlide 4Human Y chromosomeSlide 6Genetically, what determines gender in mammals?XX (+SRY) miceDosage CompensationX InactivationWhich X gets inactivated?Slide 12Genetic MosaicsTortoiseshell (calico) coat colorSlide 15Slide 16Slide 17Carbon CopyX inactivation is different in marsupialsSex chromosome aberrationsAnnouncementsHomework due 9:00 Thursday–only your first grade will count!Review Session Sunday 3:00 to 4:00 PM124 Burrill Hall Exam Tuesday 9:00 AM, in Lecture roomSex Chromosomes and Sex DeterminationX and Y are clearly not homologous chromsomes.How do they segregate normally at Meiosis?During what part of Meiosis do they pair and then segregate?Human Y chromosome•Yellow: pseuoautosomal regions•Red: genes with homologs on the X chromosome•Blue: genes without homologus on the XGenetically, what determines gender in mammals?Presence of a single gene (SRY) that usually, but not always, occurs on the Y chromosome.If the Y chromosome is missing (this gene deleted) or has a non-functional mutation in the gene, an XY individual can be a perfectly normal female.If the SRY gene becomes translocated to another chromosome, an XX individual can be a phenotypically normal (but sterile) male.XX (+SRY) miceDosage CompensationDo males have half as much of the products of genes on the X as do females?X InactivationInterphase: Chromomes can’t be stained, but a dark-staining body is visible in the nuclei of cells of female mammals Barr Body: Inactive XWhich X gets inactivated?Mary Lyon & Lianne Russell (1961) proposed that one or other of X becomes inactivated at a particular time in early development. Within each cell,which X becomes inactivated is ____________.As development proceeds, all cells arising by cell division after than time have _______ _________________.In 64-cell embryosAdult female mammals are ___________ for genes on the X chromosome.Genetic MosaicsCalico cats are almost always ____________.One X chromosome carries the allele for black coat colorThe other X chromosome carries the allele for orange coat colorIn 64-cell embryos, one of each pair of X chromosomes and its genes are _____________ ________________.Daughter cells inherit active or inactive X chromosomes, creating a cat with patches of coat colorXOXoTortoiseshell (calico) coat colorallelealleleTortoiseshell (calico) coat colorTortoiseshell (calico) coat colorCarbon CopyX inactivation is different in marsupialskangaroos, wombats, bandicoots, opossumsSex chromosome aberrations47,XXY Klinefelter syndrome45,X Turner Syndrome (XO)malefemaletall statureshort staturetestes do not maturerudimentary ovariessterilesterilelowered IQ is commonIQ typically normal1/700 male births1/3000 female births47,XYY Double-Y syndrome47,XXX Trisomy-X syndromemaleabove average height, otherwise phenotypicallynormal. At one time, it was claimed that XYY males are proneto violent or antisocial behavior, based on elevatedincidence of 47,XYY among incarcerated men. Nowthought to be due to higher incidence of moderatemental retardation than for XY males.many phenotypically normalthe frequency of lowered IQ is higher than amongXX


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UIUC IB 201 - Sex Chromosomes and Sex Determination

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