HMB265H1 Lecture Notes - Pax6, Cooperative Binding, Epigenetics

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1 Apr 2011
School
Department
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LECTURE 22
Final Exam:
๎€April 12th from 2-4pm
๎€Both sections
๎€20-25% based on first semester
๎€Rest based on second semester
Tutorial
๎€Quiz โ€“ epigenetics and genetics
oLook over calculations for odds ratios and lod ratios
oQuantitative genetics calculations
Regulated gene expression
๎€All start with same types of cells, stem cells, containing same amount of genes,
DNA
๎€Genes regulated by other factors and proteins within genome
๎€Model organisms used to study development
oZebrafish
oNematode c elegans
oArabidopsis
oMouse
oFruit flies
oUsed to
๎€Small size so easily manipulated
๎€Look at flies and mice to drive development in humans
โ€ขPathways and genetic mechanisms conserved
โ€ขWhat occurs in flies, occur in humans
โ€ขGenomes sequenced so can find genes with mutant
phenotypes
All living forms are related
๎€Fly
๎€Loss of function of eyeless gene in drosophila = > no eye or small eye forming
๎€Pax-6 gene is homolog of eyeless
๎€Analog in humans called Aniridia
๎€MUTATIONS
oNo functional copies of aniridia eyes โ€“ embryos have no eye formation,
lethality in utero
๎€Homozygous loss of function leads to embryonic lethality
oHeterozygote โ€“ lack one or two irises
๎€One wildtype only
Knockout โ€“ reverse genetics
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๎€To see what genes are important in what pathways? What defects result? Genes
important for what?
๎€Forward geneticsโ€ฆmutagenize model organisms
oCross mutant mice with wildtype mice to perform phenotypic analysis
๎€Drosophila so important
oBest genetic model organism THUS best model to study function of genes
in development
oEmbryo to adult = 10-11 days at 23 degrees C
oGenes positioning relationship btw axis conserved among species
๎€Correct formation of axises in embryo lead to normal adult fly
1995 โ€“ Nobel prize for discoveries concerning early development of drosophila
embryos
๎€Found the genes controlling axis and that they were conserved
Different classes of drosohpila genes important for patterning of embryo
๎€Anterior posterior pattern development focused today
oFirst class is maternal effect genes
๎€Maternal effect mRNAs deposited in early embryo by mother
๎€These genes direct formation of anterior, posterior axis in fly
๎€Genotype of mother important
โ€ขIf mother has at least one wildtype copy of maternal effect
gene, then will have functional maternal affect protein
โ€ขIf lack protein, then embryo will lack functional maternal
affect protein, resulting in mutant embryo
โ€ขFather does not matter โ€“ true for many species, including
humans
โ€ขMotherโ€™s genes that set up axis
oMust have at least one wildtype copy in order to have
normal maternal affect proteins
๎€Present in concentration gradient
โ€ขBicoid = maternal effect gene, deposited and localized to
anterior portion of drosophila embryo
โ€ขGradient
oEmbryo synsinitia
๎€Nuclear division without cytoplasmic division
๎€One embryo has many nuclei, but not cellular
division
๎€So easy for RNAs deposited to diffuse from
one end to other
๎€If bicoid at anterior end, see gradient of
expression from antieror to posterior
๎€Very little expression when get past embryo
๎€Embryos lacking bicoid protein because
mother had no functional copies of gene
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Document Summary

quiz epigenetics and genetics: look over calculations for odds ratios and lod ratios, quantitative genetics calculations. all start with same types of cells, stem cells, containing same amount of genes, genes regulated by other factors and proteins within genome. model organisms used to study development: zebrafish, nematode c elegans, arabidopsis, mouse, fruit flies, used to. Look at flies and mice to drive development in humans: pathways and genetic mechanisms conserved, what occurs in flies, occur in humans, genomes sequenced so can find genes with mutant phenotypes. Loss of function of eyeless gene in drosophila = > no eye or small eye forming. mutations: no functional copies of aniridia eyes embryos have no eye formation, lethality in utero. homozygous loss of function leads to embryonic lethality: heterozygote lack one or two irises. Forward genetics mutagenize model organisms: cross mu tant mice with wildtype mice to perform phenotypic analysis.

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