L10 Bizarre Deviants Pt1

L10 Bizarre Deviants Pt1 - Bizarre Deviants! Non-Mendelian...

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Unformatted text preview: Bizarre Deviants! Non-Mendelian inheritance Pt. 1 1 Last Time Breaking the Law of Independent Assortment What is linkage? Creating maps Frequency of recombination Determining the order of genes on chromosome 2 Bizarre deviants! The Maternal Effect Genetic examples Molecular basis for inheritance Maternal effect in flies Epigenetic Inheritance Dosage compensation Molecular basis for dosage compensation 3 Maternal Effect Mom’s genes count, dad’s and offspring’s genes don’t Classic example: direction of coiling of snail shells http://imagecache2.allposters.com/images/ pic/HAD/5705~Maternal-AffectionPosters.jpg 4 Shells can be left or right coiled P F1 5 Reciprocal cross P F1 http://floridasoftwater.com/imgs/services/Confused_Guy.jpg 6 “Is coiling direction due to a maternal effect?” Hypothesis: If Mom is D, then offspring are dextral If Mom is d, then offspring are sinistral Dad’s genes have no effect on phenotype Alfred Sturtevant http://www.nature.com/ng/journal/v34/n3/images/ng0703-242-I1.jpg 7 Is the hypothesis supported? YES! F1 Dd F2 Dd F3 3:1 dextral: sinistral 8 The maternal effect mechanism 9 But how does this affect body plan? D protein product - controls orientation of mitotic spindle at 2 cell stage. Dextral Sinistral 10 Maternal effect genes: bicoid Bicoid - Drosophila gene that specifies “front” (anterior) from back (posterior) anteroposterior axis dorsoventral axis 11 Fly development Morphological changes during fly development Egg Larvae Adult 12 Bicoid expression pattern RNA localization Protein localization 13 bicoid mutants Lack of bicoid - no anterior specified 14 Tips for detecting the maternal effect Do reciprocal crosses! Examine phenotype of offspring relative to the genotype of the mother dd DD DD dd 15 Epigenetic inheritance Genes are turned ‘off’ in a way that permanently alters their expression in an individual Two kinds of epigenetic inheritance: 1. dosage compensation (today) 2. genomic imprinting (next time) 16 How is this possible? www.pbs.org 17 Dosage compensation Mammals: XX XY Flies: XX XY http://loeppert.net/images/fly_icon.jpg http://www.serendipitykids.ie/shop/images/girl%20icon.jpg 18 random X inactivation paternal X inactivation http://www.alerttoday.com/wp-content/uploads/2007/12/wonder-woman.jpg http://imagecache2.allposters.com/images/pic/PTGPOD/541447~Australian-Kangaroo-Posters.jpg 19 X-inactivation Barr body = condensed X chromosome inactive active 20 Female mammals are functionally mosaic One of two X chromosomes becomes randomly and irreversibly inactivated during early development and is stably inherited by daughter cells 21 Both X chromosomes are active early in development (8 cell stage) One X is inactivated 22 How is X inactivated? Normal female Normal male Turner Syndrome (female) Triple X Syndrome (female) Klinefelter Syndrome (male) Chromosomes XX XY X0 # X’s 2 1 1 # Barr bodies 1 0 0 XXX XXY 2 2 2 2 23 X-inactivation center (XIC) XIST RNA http://spot.colorado.edu/~strauswm/images/Xist_Bodies.gif 24 X-inactivation center (XIC) Tsix is only expressed from active X chromosome Xist is only expressed from inactive X chromosome 25 X-inactivation center (XIC) TF? X active (strong) X inactive (weak) 26 Genes on inactive X are not completely ‘off’ pseudoautosomal genes: Located on both Y and X Regions of homology Region of pairing during meiosis 27 Summary The Maternal Effect - offspring express phenotype of mother regardless of offspring’s genotype Result of diploid nurse cells, which load protein and RNA into the egg cell Maternally loaded bicoid RNA specifies anterior end of developing fly embryo Epigenetic Inheritance - modified genes change expression (and phenotype) X-inactivation (dosage compensation) results in phenotypically mosaic females 28 Ungraded problems Go through Chapter 7 S1 Try Chapter 7 C2, C4 Try Chapter 7 E1, E6 29 Next Time Bizarre Deviants Pt2: More epigenetic inheritance Extranuclear inheritance http://www.willowaynurseries.com/Images/EuonymusGoldSplash.jpg 30 ...
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