Presentation on theme: "Announcements We have decided to halt our efforts with the yw crosses, due to uncooperative yw females, frustration, and lack of motivation (we KNOW the."— Presentation transcript:
1 AnnouncementsWe have decided to halt our efforts with the yw crosses, due to uncooperative yw females, frustration, and lack of motivation (we KNOW the expected results). There will be no assignment due for this lab activity. You are responsible for understanding the expected results and how to calculate recombination frequencies and map distance (ie. flylab 6).You should continue your X-linked crosses.Vote on when to review for exam 2 (10/17, 10/18) - Mon. evening or in class Wednesday. If we review in class Wed, then class meets Fri. If we review Mon., then class meets Wed.Is there a serious problem taking the exam on Thurs. or Fri.???Reminder that homework is due next Tues., Wed.Quiz in lab next week; be prepared - pick up lab7 overview and read it.Practice problems for Ch.8: 1,3,9,11; Ch.9: 4,8,10
2 Review of Last Lecture 1.Quick review of conjugation: F-, F+, Hfr 2. Transformation: a different process of recombination, can be used to map genes3. Bacteriophages are viruses that use bacteria as hosts; they can mediate bacterial DNA transfer - transduction4. Extrachromosomal inheritance: Phenotype of maternal parent is solely responsible for phenotype of offspring - example of maternal inheritance of chloroplasts
3 Outline of Lecture 16I. Two more examples of extrachromosomal inheritance: mitochondria and “maternal effect”II. Modes of sex determinationIII. Humans and sex determinationIV. Dosage compensation
4 I. Mitochondrial Heredity About 30,000 genes on 23 human chromosomes (3.3 billion base pairs/haploid cell)Mitochondrial Genome contains 37 genes:13 code for some of the proteins involved in oxidative respiration22 tRNA genes2 rRNA genessome proteins involved in mt protein synthesis16,569 base pairs, circular
5 Human Mitochondrial Diseases Are maternally inherited: only offspring of affected mothers are affectedShow deficiency in mitochondrial functionAre caused by a mutation in a mitochondrial geneExample: myoclonic epilepsy and ragged red fiber disease (MERRF)Deafness, dementia, seizuresPoint Mutation in a mitochondrial tRNA
6 Other Human Mitochondrial Diseases Leber’s Hereditary Optic Neuropathy (LHON)Sudden bilateral blindnessPoint mutation in small subunit of NADH dehydrogenaseKearns-Sayre Syndrome (KSS)Symptoms in eyes, muscles, heart, brainDeletion mutation in mtDNA
7 Maternal Effect: Snail Coiling Pattern of offspring determined by genotype of mother, regardless of phenotypeDDdddextralsinistralD egg, d spermD sperm, d eggDdDddextralsinistral
8 Maternal Effect Genes in Drosophila Development Discovered by Edward Lewis, Christiane Nusslein-Volhard and Eric Weischaus (Nobel Prize in Physiology or Medicine, 1995)Gene products deposited in egg by cells of mother’s ovary.These genes set up the first embryonic axes: dorsal-ventral and anterior-posterior and control later zygotic genes.
9 Gene Map of the Y Chromosome II. Sex DeterminationGene Map of the Y Chromosome
10 Modes of Sex Determination XX/XO (Protenor)absence of second X chromosome determines malenessas in Caenorhabditis elegansXX/XY (Lygaeus)presence of Y chromosome determines malenessin mammalssometimes females are heterogametic sex
14 Klinefelter Syndrome (47, XXY) Some male dev.but no sperm, andsome female dev. too.2 in 1000 male births
15 Turner Syndrome (45, X) Female dev. but no eggs. 1 in 3000 female births
16 The Odyssey of the Germ Cells Primordial Germ Cells are set aside early in embryonic developmentPMG’s migrate to embryonic kidney ridges:If cells are XY, medulla develops into testes under direction of male hormones around week 7If cells lack a Y, cortex develops into ovary, also under active hormonal controlActive gene expression required in either caseDuct differentiation:If XY, Wolffian ducts > epididymis and vas deferensIf no Y, Mullerian ducts > oviduct
17 The Human Y ChromosomeNRY is non-recombiningregion of Y
18 Testis-Determining Factor Was the object of an intense search.SRY gene on the Y chromosome was identified as the gene that codes for TDF:SRY is translocated to X in rare XX malesSRY is absent from Y in rare XY femalesThe “home run” experiment by Koopman et al. used transgenic mice.
19 The Transgenic Sry Experiment: How It Was Done Reference: Nature 351:117 (1991)Nuclei of fertilized XX eggs were injected with Sry gene, then the eggs were transplanted to surrogate mothers.Sry gene then randomly incorporated into a chromosome and was inherited in subsequent cell divisions.Animals karyotyped after development to adult.
20 Genotypically Female Mice Transgenic for SRY are Phenotypically Male XY maleXX male
21 IV. Dosage Compensation Shouldn’t XX females produce twice the amount of X-linked gene products as XY males?No, because XX females “compensate” by inactivating one of their X chromosomes to make a single “dosage” of X-linked genes.
22 Barr Bodies are Inactivated X Chromosomes in Females
23 The Lyon Hypothesis of X Inactivation Proposed by Mary Lyon and Liane Russell (1961)Inactivation of X chromosome occurs randomly in somatic cells during embryogenesisProgeny of cells all have same inactivated X chromosome as original, creating mosaic individual
24 Lyon-Hypothesis: X-inactivation A precursor cell to all coat colorcellsRandom inactivation
25 Mosaicism Reveals the Random Inactivation of one X chromosome Regions wheresweat glandsare absent.
26 Bilateral Gyandromorph (both Male and Female Genotypes) Occurs from loss of one X (with wildtype alleles) at1st mitotic division during development, oriented bilaterally.Female (XX) half:heterozygous for bothmarkersMale (XO) half:white,miniature wing