GCD 3022 1st Edition Lecture 10 Outline of Last Lecture I Introduction a Maternal effect and epigenetic inheritance b Extranuclear inheritance II Maternal Effect a Definition b Explanation c Example water snail III Epigenetic Inheritance a Definition b Explanation of Causes c Dosage Compensation i Definition d X inactivation i Barr body 1 Table ii Lyon hypothesis iii Mechanism Outline of Current Lecture These 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 I Genomic Imprinting a Definition b Three stages c Example Igf 2 in mice II Imprinting and DNA methylation a Imprinting of genes b Methylation III Extranuclear Inheritance a Definition b Organelles c Mitochondria d Chloroplasts IV Maternal Inheritance a Definition b The four o clock plant c Cellular explanation Current Lecture I Genomic Imprinting a A segment of DNA is marked and the effect is maintained throughout the life of the organism inheriting the marked DNA i Follows a non Mendelian pattern of inheritance ii Monoallelic expression Depending on how the genes are marked the offspring expresses either the maternally inherited or paternally inherited allele not both iii Permanent in the somatic cells of an animal but marking of alleles can be altered from generation to generation II III b Three Stages imprinting is an epigenetic process at the cellular level i Establishment of the imprint during gametogenesis ii Maintenance of the imprint during embryogenesis and in the adult somatic cells iii Erasure and reestablishment of the imprint in the germ cells c Example Igf 2 in mice i Igf 2 gene encodes a growth hormone called insulin growth factor 2 A functional Igf 2 gene is necessary for normal size ii Imprinting results in the expression of the paternal but not the maternal allele paternal allele is transcribed into RNA maternal allele is not transcribed iii Igf 2m is a loss of function allele that does not express a functional Igf 2 protein results in dwarfism depending on if the mutant allele was inherited from the father or mother Imprinting and DNA methylation a Imprinting of genes i Involves a marking process called methylation ii The imprinting of several genes involves an imprinting control center ICR located near the imprinted gene which is methylated in the oocyte or the sperm not both iii The ICR contains binding sites for one or more transcription factors that regulate the imprinted gene b Methylation i During gamete formation either the oocyte egg or the spermatocyte sperm is methylated not both this depends on the gene in question ii If one is methylated it is called de novo methylation and causes an inactivation of transcription from that gamete when it attempts to pass the genetic information on to the offspring iii Ex if the sperm is methylated then the paternal chromosome that is inherited by the offspring will not exhibit the paternal phenotype for that gene and will exhibit the maternal phenotype Extranuclear Inheritance a Inheritance patterns inheriting genetic material outside the nucleus names mitochondria and chloroplasts Also known as cytoplasmic inheritance i Genetic material is located in a region called the nucleoid can contain several copies of the chromosome and an organelle can contain more than one nucleoid ii Genome is composed of a single circular chromosome containing doublestranded DNA b Mitochondria organelle of extranuclear inheritance in animals IV i Main function of mitochondria is oxidative phosphorylation to produce ATP energy for the cell ii Genetic material in mitochondria is referred to mtDNA carries relatively few genes mostly rRNA and tRNA for oxidative phosphorylation iii Most mitochondrial proteins are encoded by genes in the nucleus These proteins are made in the cytoplasm then transported into the mitochondria c Chloroplasts organelle of extranuclear inheritance in plants i Main function of chloroplasts is photosynthesis ii Genetic material is referred to as cpDNA about 10x larger than mitochondrial genome of animal cells iii cpDNA carries between 110 and 120 different genes also tRNA and rRNA genes polypeptides required for photosynthesis iv As with mitochondria many proteins are encoded by genes in the nucleus These proteins are made in the cytoplasm and transported into the chloroplast Maternal Inheritance a Phenotype of the offspring depended solely on the maternal parent and not at all on the paternal parent different than maternal effect b Four o clock plant pigmentation in this plant shows this type of non Mendelian inheritance i Discovered by Carl Correns ii Leaves can be green wild type white mutant or variegated called heteroplasmy green white patches iii Phenotype of the leaves can be explained by the types of chloroplasts found in leaf cells If variegated the leaf starts out green and turns variegated while maturing due to the irregular distribution to daughter cells