Extra credit problem for Lecture #6Sex Determination in Drosophila and other organismsPowerPoint PresentationX chromosome: Autosome BalanceSlide 5Slide 6Slide 7Other kinds of sex determinationSlide 9In some organisms, sex is not ‘determined’ at all!Coral GobyAnd some species are all female!Genomic ImprintingSlide 14Disease can result from imprintingGenetic Linkage and MappingSlide 17Slide 18Slide 19Slide 20Meiosis: Prophase ICloser lookNotationDihybrid CrossSlide 254 gamete types, equally frequentF2 of dihybrid cross when genes not linkedExtra credit problem for Lecture #6How is sex determined in Drosophila melanogaster?For extra credit question, please use the index cards provided. •Print your name and section # at top of card.•Thanks!Sex Determination in Drosophila and other organismsX chromosome: Autosome BalanceIn Drosophila, sex is determined by the ratio of the number of X chromosomes to the number of sets of autosomesOther kinds of sex determination•Grasshoppers, crickets, roaches: XO•Bees, ants, wasps: haplodiploidy•Snakes: ZZ/ZW•Lizards: both XX/XY and ZZ/ZW systems•Crocodiles, most turtles, and some lizards, sex is determined by the incubation temperature during a critical period of embryo development. This is known as temperature-dependent sex determination (TSD).Some lizards? Turtles Lizards, Turtles, CrocodiliansIn some organisms, sex is not ‘determined’ at all!Some fish change sex as they get older or larger. In clown fish, largest group member is female, second largest is male, and all others are non-breeding. Sometimes the largest fish in the group will become male, all others will be female (wrasses).Coral GobyGobiodon histrioMonogamous pairsIf mate dies or leaves, resident will court next fish to come by, one will change sex to accommodate.And some species are all female!Asexual Cnemidophorus species are all female; reproduce via parthenogenesis.Diploid or triploid eggs develop directly from oocytes via pre-meiotic endomitosis, no cellular/nuclear division.At meiosis, identical rather than homologous chromosomes pair, and then segregate.All offspring are females genetically identical to their mothers. Cnemidophorus species tend to have extremely low levels of genetic diversity.From A. J. Collum, Creighton Univ, http://biology.creighton.edu/faculty/cullum/CnemmyInfo.htmlGenomic ImprintingDifferential expression of genetic traits depending on whether the trait has been inherited from a mother or a father.Disease can result from imprintingQuickTime™ and aTIFF (LZW) decompressorare needed to see this picture.QuickTime™ and aTIFF (LZW) decompressorare needed to see this picture.QuickTime™ and aTIFF (LZW) decompressorare needed to see this picture.Paternal SNRPN Gene inactive bymutationPaternal SNRPN gene active(chrom. 15)Maternal SNRPN Gene inactive by imprintingFertilizationQuickTime™ and aTIFF (LZW) decompressorare needed to see this picture.Both copiesinactivePrader-WilliSyndromeShort statureMild retardationPoor muscle toneCompulsive eatingGenetic Linkage and MappingMeiosis: Prophase ICloser lookNotation—•—————A__•_______AaAaDiploidAdultHaploid gametes(single chromatid)—•—————Two homologouschromosomes,four chromatids total__•_______A__•_______a__•_______a1/2 A : 1/2 aDihybrid CrossAA BB Female aa bb Male A B a b—•————— ——•————— —•————— ——•————— P: —•————— ——•————— —•————— ——•————— A B a bGametes: Egg (A B) Sperm (a b) A B a b—•————— ——•———— —•————— ——•————A B—•————— ——•————— F1: —•————— ——•————— a bafter the S phaseF1 adult4 gamete types, equally frequent A B—•————— ——•———— A b—•————— ——•———— a B—•————— ——•———— a b—•————— ——•———— A B—•————— ——•————— F1: —•————— ——•————— a bParentalRecombinantRecombinantParentalF2 of dihybrid cross when genes not linked•What proportion of the gametes of the double heterozygote are recombinant?50
View Full Document
Unlocking...