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Bi205-10 Extranuclear inheritance

Bi205-10 Extranuclear inheritance. Plant cell stained with DAPI-a fluorescent stain for DNA (blue). Chloroplast naturally fluoresce red. nucleus. chloroplast. Chloroplasts and mitochondria have circular genomes. How was cytoplasmic inheritance discovered?.

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Bi205-10 Extranuclear inheritance

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  1. Bi205-10 Extranuclear inheritance

  2. Plant cell stained with DAPI-a fluorescent stain for DNA (blue). Chloroplast naturally fluoresce red. nucleus chloroplast

  3. Chloroplasts and mitochondria have circular genomes.

  4. How was cytoplasmic inheritance discovered? C. CORRENS (1909) and E. BAUR (1909, 1910) described crossings, for which the Mendelian laws did not apply.

  5. Looked at inheritance of variegated leaves

  6. Some plants have different types of leaves on different branches. Allow them to self pollinate and collect. Cross pollinate to check results.

  7. Regardless of the type of pollen that was used to fertilise the flowers: Branches with white leaves gave only white leaf progeny. Branches with green leaves gave only green progeny. Branches with variegated leaves gave green, white and variegeted progeny.

  8. conclusion • Phenotype does not depend on nuclear genotype (pollen not involved) • Must be dependent on cytoplasm of female organs in the flower. • Cytoplasmic inheritance.

  9. Caused by segregation of different types of chloroplasts Leaf variegation

  10. Today we know that the white patches are caused by a mutation in chloroplast genes coding for chlorophyll pigments.

  11. Cytoplasmic male sterility in (CMS) maize • Observed by Marcus Rhoades in 1933. • Maize has both male (tassel) and female flowers (cob). • CMS plants fail to produce viable pollen in tassels, but are fertile as females. • Used in agriculture to generate hybrids with desirable characters.

  12. Mitochondrial DNA • Predominantly maternally inherited in plants and animals • Haploid (one copy in each individual) • No recombination • Location of oxidative phosphorylation (OXPHOS), which is vital for metabolic activity of somatic cells and gametes • mtDNA encodes 13 of 67 components of the OXPHOS system

  13. CMS phenotype shows maternal inheritance. • All progeny of CMS plants have CMS. • Crossing CMS plants to male fertile plants for many generations does not produce male fertility. • CMS results from a mutation in a mitochondrial gene whose function is vital for pollen maturation.

  14. Interaction between nuclear and cytoplasmic genes • In certain crosses involving CMS-T plants male fertility can be restored by alleles of two nuclear genes known as restorer of fertility genes (Rf1 and Rf2) • Dominant alleles at both Rf1 and Rf2 are necessary to restore fertility.

  15. Maternal inheritance of mtDNA mother father m2 m1 m1 m1 All children inherit their mother’s mtDNA type

  16. Wallace, D.C. 1999. Mitochondrial diseases in man and mouse. Science283:1482-1488. • ADPD • late-onset Alzheimer’s • CEPO • chronic progressive external ophthalmopelia • LHON • Leber’s hereditary optic neuropathy • NARP • neurogenic muscle weakness, ataxia, and retinitus pigmentosa.

  17. mtDNA and Male Fertility Sperm are motile and powered by mitochondria; even small reduction in power may reduce sperm mobility and reduce fertility.

  18. Traits carried by infectious agents Tracy Sonneborn (1904-1981) working on single celled protosaon, Paramecium.

  19. Paramecium conjugation • Macro and Micro nucleus • Macro nucleus is polyploid and disintegrates during conjugation • Micronucleus is diploid and undergoes meiosis giving rise to 4 micronuclei in each cell, 3 of which disintegrate • remaining nucleus undergoes mitosis get 2 haploid micronuclei per cell • nuclei in two conjugating cells swap then fuse giving rise to 1 diploid nucleus per cell • additional mitotic divisions and nuclear fusion will give rise to macro and micro nuclei in each cell

  20. http://www.sparknotes.com/biology/microorganisms/protista/section2.rhtmlhttp://www.sparknotes.com/biology/microorganisms/protista/section2.rhtml

  21.  Sonneborn discovered and studied killers, Paramecia that produced a toxin that could kill other strains of paramecia yet that are resistant to their own toxin. • Crosses showed the presence of nuclear genes necessary for the perpetuation of the killer trait and also showed the presence of an essential cytoplasmic element that he called "kappa.“ • Strains that lost kappa became sensitive to the toxin. • Kappa proved puzzling to Sonneborn for many years, but it was finally shown in other laboratories that kappa is an example of a symbiotic bacterium able to live only in Paramecium.

  22. Under certain circumstances a mating between a sensitive and a killer strain can be achieved • The sensitive cell survives and becomes a killer cell only if it receives cytoplasmic kappa particles • Kappa particles were later shown to be an endosymbiotic bacterium

  23. Endosymbiont theory on origin of mitochondria and chloroplasts http://en.wikipedia.org/wiki/Endosymbiotic_theory Proposed as early as 1883 but formalised and popularised by Dr Lynn Marguilis in 1960’s (published in 1970) Organelles originate by endocytosis and subsequent symbiosis between bacterial and eukaryotic cell.

  24. Opposite view • Autogenous model = eukaryotic cells evolved by specialisation of internal membranes derived from prokaryotic plasma membranes. In this model most endomembranous structures are believed to have differentiated from invaginations of the prokaryotic plasma membrane. The double-membrane organelles (mitochondria and chloroplasts) may have evolved by secondary invagination or more complex membrane folding.

  25. Evidence • Mitochondria and chloroplasts are not assembled by the cell but arise by the division of existing organelles by simple fission-like bacteria • They have their own DNA, RNA and ribosomes. DNA sequence of organelle genes resemble eubacterial sequence. • Organelle division occurs throughout the cell cycle not only in S phase • Organelles are surrounded by double membrane. The inner membrane differs from other membranes in the cell. • Several examples of bacteria and algae that can establish symbiotic relationships with eukaryotic cells.

  26. Current Endosymbiont Bacterial cell Photosynthetic Cyanobacteria in cytoplasm of flagellated protozoan Cyanophora.

  27. Maternally inherited cytoplasmic factors • Produce inheritance patterns strictly dependent on the genotype of the mother, known as maternal effects. • Phenotype does not depend on the genotype of the individual or genotype of the father.

  28. Coiling in the snail Limnea peregra The direction of shell coiling is controlled by a single gene. The phenotype of an individual is determined by the genotype of its mother. Right (dextral) coiling (D) is dominant to left (sinistral) coiling (d).

  29. Maternal effect genes • The genotype of a mother determines the structure of the eggs that she produces. • Cytoplasmic factors present in the egg. • Control early stages of development.

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