GCD 3022 1st Edition Lecture 11Outline of Last Lecture I. Genomic Imprintinga. Definitionb. Three stagesc. Example: Igf-2 in miceII. Imprinting and DNA methylationa. Imprinting of genesb. MethylationIII. Extranuclear Inheritancea. Definitionb. Mitochondriac. ChloroplastsIV. Maternal Inheritancea. Definitionb. The four o’ clock plantOutline of Current Lecture I. Maternal Effecta. Nurse Cellsb. DrosophilaThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.c. Water Snailsi. F1 genotypes and phenotypesii. F2 genotypes and phenotypesiii. Percentage of F2 that are dextral iv. F3 generationv. Phenotypic ratio of F3 generationII. Epigenetic Inheritancea. Examples of epigenetic inheritanceb. Genomic imprintingIII. Igf2+ and Igf2- and genomic imprintinga. Scenario 1b. Scenario 2c. Imprinted genesd. Scenario 3IV. Types of Inheritancea. Example 1b. Example 2c. Example 3V. De novo DNA methylationVI. The Lyon HypothesisVII. Barr BodiesVIII. Reciprocal Crossa. Definitionb. Reciprocal cross scenarioc. Maternal inheritanceCurrent LectureI. Maternal Effecta. Nurse cells: able to express both alleles present in the maternal genome. The only time this makes a difference in the outcome of the offspring is if the mother is heterozygous. b. Drosophila: a drosophila embryo dies during early embryogenesis due to a recessive maternal effect called bicoid. The wild-type is bic+. The genotypes of the embryo’s mother and grandmother would have to be bic-bic- and bic+bic- respectively because the grandmother would have to pass on the recessive allele to the mother of the generation in question. Since the offspring died, that means that it’s phenotype reflected the mother’s genotype, which would have had to have been bic-bic-. c. Water Snails: A sinistral male (dd) and dextral female (DD) mate to produce offspringi. What are the genotypes and phenotypes of the F1 generation?1. The result of a cross between two homozygotes (DDxdd) will result in all Dd offspring. Since this is a maternal inheritance pattern, the F1 generation will all be dextral. ii. If the F1 progeny are allowed to mate with one another,1. What are the possible F2 genotypes and what ratios would be expected?a. The genotypic ratio would e 1DD:2Dd:1dd (using a Punnettsquare of DdxDd)2. What percentage of the F2 snails will have a dextral coiling pattern? a. Mating the F1 progeny to each other will yield an F2 generation that all have a dextral coiling pattern because all of the F1 females carried a D allele. iii. If the F2 generation is allowed to interbreed to produce an F3 generation1. What percentage of sinistral heterozygotes in the F3 generation had a mother with the dd genotype?a. The genotype of the progeny is not important. If the snail is sinistral it’s the mother who had to be dd so that answeris 100%.2. What is the phenotypic ratio of dextral:sinistral in the F3 generation?a. 3:1 (dextral to sinistral)II. Epigenetic Inheritancea. Examples of epigenetic inheritance: imprinting, X inactivationb. Genomic imprinting: although two copies of the gene in both female and male parents appear wild type by sequence analysis, only the maternal allele is expressed in the offspring. III. Igf2+/Igf2- and genomic imprintinga. Scenario 1: if an Igf2-/Igf2- female is crossed to an Igf2-/Igf2+ male, what is the predicted outcome?i. Half the offspring would be normal, and half would be dwarf. b. Scenario 2: If an Igf2+/Igf2+ female is crossed to an Igf2-/Igf2- male, what is the predicted outcome?i. All the offspring would be dwarf.c. Imprinted genes: provide examples of epigenetic inheritance and are near differentially methylated regionsd. Scenario 3: you cross a dwarf female mouse with a normal male mouse and get 50% dwarf and 50% normal F1 progeny. You then randomy select 10 different pairs of normal sized male and female mice from the F1 generation and mate them to each other to generate an F2 generation. In each individual mating you always get a 50:50 ratio of dwarf to normal mice. i. Note: the IGF2 gene is an imprinted gene where the copy inherited from the male is active and the copy from the female is silenced. Igf2 is the wild type and Igf2- is the recessive (mutant) allele. 1. What were the genotypes of the male and female mice in the P1 generation? a. Since half the progeny are dwarf and the male is the only parent that influences how the Igf2 gene is expressed, thenthe male parent must be heterozygous in order to achieve 50% of the F1 progeny as dwarf. (try making a Punnett square)b. The female parent is dwarf, so she can be either homozygous recessive or heterozygous (where she inheritsthe recessive allele from her father). c. Try making a table of the possible F1 progeny if the motherwas heterozygous and if she was homozygous. Count the ratio of phenotypes (dwarf:normal) for both tables and compare to determine the more likely genotype of the mother.IV. Types of inheritancea. Example 1: phenotype of the offspring is totally dependent on the genotype of the mother maternal effect.b. Example 2: phenotype of the offspring follows the phenotype of the mother maternal inheritance.c. Example 3: phenotype of the offspring is dependent on the genotypes of the mother and the father Mendelian inheritance.V. De novo methylationa. In what types of cells would you expect de novo DNA methylation that regulates imprinting to occur?i. De novo methylation would not occur in somatic cells, but would occur in germ cells. VI. The Lyon hypothesisa. Attempts to explain the molecular mechanism of dosage compensation (X-inactivation)VII. Barr bodiesa. The number of Barr bodies in an individual is determined by the number of X chromosomes present. An individual with an XXX genotype would have 2 Barr bodies (n-1). VIII. Reciprocal Crossa. Definition: two parallel crosses that involve the same genotypes of the two parents, but their sexes are opposite in the two crosses. For example, the reciprocal cross of female: BB x male: bb is female: bb x male: BB. b. A gene is found as a wild-type dominant allele (B) and recessive mutant allele (b).What would be the expected outcomes (genotypic and phenotypic) of reciprocal crosses if a true-breeding wild-type individual was crossed to a true breeding mutant individual?i. If the gene was inherited in a simple autosomal pattern of inheritance:1. The result of one cross will be the same as the