BIO 305 1st Edition Lecture 8 Outline of Last Lecture I. Sex DeterminationII. Dosage CompensationIII. Sex Determination in Drosophila and HoneybeesOutline of Current Lecture I. Extranuclear InheritanceII. Chloroplast vs. Mitochondrial Genome and InhertanceIII. Other forms of Non-Mendelian Inheritance: A. Three Examples: Neurospora S. Cerevisae, and HumansB. Mitochondrial DNA MutationsC. Maternal Effect and Shell CoilingIV. Vocab and Sample QuestionsCurrent LectureI. Extranuclear InheritanceKnow the three types of Non-Mendelian Inheritance (cytoplasmic inheritance, maternal effect, and imprinting) and how the affect the ratio of phenotypes of progeny.Cytoplasmic Inheritance: The mitochondria and the chloroplast contain DNA (mtDNA and cpDNA, respectively)Three rules of Cytoplasmic Inheritance:1) Ratios typical of Mendelian segregation do not occurReason: Segregation via meiosis does not occur, thus neither does ratio2) The children show only one of the parent’s phenotype.Reason: Reciprocal crosses show uniparental inheritance because zygotes receivecytoplasm from the mother3) Parental leakage occurs at low levels and is transientReason: Mechanisms that degrade paternal and mt/cpDNA may existExample: Variegated 4-o-clock plantsThe plant shows some leaves that are green, some that are white, and others that are patchy. This is because some of the leaves have normal, functioning chloroplasts (thus green and photosynthetic), others are variegated and have mixed chloroplasts (white/green), and the others have mutant non-functional chloroplasts (white and non-photosynthetic)Reasoning: (Rule 2) Chloroplasts are inherited via the seed cytoplasm, thus the ovule source determines the phenotype. Assuming pollen contributes no information, you get 3 typesof eggs from a variegated plant: normal, mutant, and mixed. Normal – chloroplasts only, Mutant – chloroplasts only, variegated – bothExample: Life Cycle of Green Algae ChlamydomonasGreen algae are a unicellular haploid organism with two different mating types (mt+ and mt-) They also possess a single chloroplast with many copies of cpDNA. When the mating types mt+ and mt- undergo syngamous mating and fuse, they undergo meiosis, and the gametes segregate in Mendelian ratios.BUT certain traits, such as antibiotic resistance are passed only through the mt+ parent.Reason: There is biased segregation of the chloroplast type, inactivation of cpDNA from mt-This reciprocal cross between streptomycin resistant and sensitive green algae shows how the resulting ratios are affected depending on whether the mt+ parent was resistant or sensitive:a) For nuclear segregation, you see a 1:1 ratio of mt+ to mt-, but for extranuclear segregation: allthe progeny are resistantb) For nuclear segregation, you see a 1:1 ratio of mt+ to mt-, but for extranuclear segregation: all the progeny are sensitiveII. Chloroplast Genome vs. Mitochondrial InheritanceCHLOROPLAST- 100-225 kb in size- circular with multiple copies- encodes some proteins of photosynthesis, DNA/RNA polymerization, tRNAs, and rRNAs- uniparental inheritance that is usually maternal- RNAs not capped often in “operons”, someintrons- Translation factors, similar to prokaryotes- Other features: Plastid genetic code GUG, UUG, AUU, CUG can initiate translation- have more genes than mitochondrial genomesMITOCHONDRION- 16 kb (smaller)- circular - 13 genes involved in oxidative phosphorylation + other genes (rRNA, tRNAs)- maternally inherited (oocyte cytoplasm to egg transmission) and doesn’t recombine!- mRNAs not capped- Translation elongation factors similar to bacterial but no Shine-Delgarno sequenceOther Key features: only females can transmit defected genes to offspring in mostspeciesBoth male and female offspring can be affectedPhenotype often related to defect in energy productionThe Mitochondron: Gene products are essential to mitochondrial function, those entering the organelle are derived from the cytoplasm and encoded by nuclear genes. Also, mitochondrion genes can be translated differently (Ex: UGA  Trp in mitochondrion, but the standard translation would be UGA  Ter)Applications of Mitochondrial DNA- Easy to isolate and copy (PCR)- Maternal inheritance and no recombination (thus clones of mother only)- However, in some species there is a mutation rate for mtDNAUseful for forensics (the mtDNA should be more exactly identical to a suspect, Maternity analysis (maternal inheritance only), Conservation genetics (cloning techniques), phylogenetic analysis (no recombination, easier to classify species into groups)Two general patterns of mitochondrial inheritance:1) Mitochondrion are inherited in a maternal fashion2) The mitochondria within an individual may or may not be genetically identical (homoplasmy/heteroplasmy)III. Non-Mendelian InheritanceA. Three Examples:Ex: Neurospora with [poky] mutation has altered mtDNA that leads to slow growth, this phenotype is cytoplasmically inherited. In reciprocal crosses, all spores in the ascus will thus match that of the mother because the mother has the nucleiEx: In S. cerevisiae, each parental cell is of equal size and contributes mitochondria to the diploid cell. Shown are the outcome of crosses involving the three types of petite mutations affecting mitochondrial function:1) Segregational – nuclear mutation and mendelian inheritance2) Neutral – lacks most mtDNA and cytoplasmic Inheritance3) Suppressive – mutant mtDNA acts dominant and cytoplasmic inheritanceEx: In humansMitochondria and their genome are transmitted from a mother to all her offspring. Thus in a pedigree, if a female is affected, should see that all her children are affected (if unaffected, all children unaffected)More notes: all diseases resulting from changes in mitochondrial DNA are fundamentallythe result of malfunctions of the respiratory chain for oxidative phosphorylationThe phenotypic effects of mitochondrial mutations reflect the extent to which a tissue relies on oxidative phosphorylation, whose sensitivity in order of greatest is:central nervous system  skeletal muscle  heart muscle  kidney  liverB. Mitochondrial DNA MutationsMutant mtDNA genomes are maintained in a heteroplasmic (multi-organelle) state and will onlycause the disease phenotype if they exceed a certain percentage of the total mtDNA genomes presentInheritance in a pedigree appears sporadic (random and few)Explanation of Pedigree: The numbers below show