Extra nuclear inheritance

Extra nuclear inheritance

1. CYTOPLASMIC INHERITANCE

2. Cytoplasmic inheritance??? Extranuclear inheritance or cytoplasmic inheritance is the transmission of genes that occur outside the nucleus. OR A form of non Mendelian inheritance in which a trait was transmitted from the parent to offspring through nonchromosomal, cytoplasmic means.

3. Introduction Mendelian inheritance patterns involve genes that directly influence the outcome of an organism’s traits and Obey Mendel’s laws. Most genes in eukaryotic species follow a Mendelian pattern of inheritance however , there are many that don’t.

4. Introduction Additional pattern of inheritance that deviate from a Mendilian pattern include… Maternal effect & epigenetic inheritance. Involve genes in the nucleus. Extranuclear Inheritance Involve genes in organelles other than the nucleus. Mitochondria Chloroplast Plasmid

5. Cytoplasmic Inheritance… The acquisition of traits or conditions controlled by self-replicating substances within the cytoplasm , such as mitochondria or chloroplasts. The phenomenon occurs in plants and some animals but has not been demonstrated in humans.

6. What is in the cytoplasm that could contain DNA??? Mitochondria Chloroplast

7. Mitochondria : Animal mitochondrial genomes are 13-18 kb in size. Fungal mitochondrial genomes are ~75 kb. Higher plant mitochondrial genomes are 300-500 kb. Each mitochondrion has 5-20 copies of the mitochondrial chromosomes. Human cells have a range of numbers of mitochondria: Liver cells have 1000 mitochondria per cell. Skin cells have 100. Egg cells have up to 10 million. Human mitochondria have 37 genes.

8. Chloroplast: Chloroplast genomes are 130-150 kb in size. Chloroplasts have more genes than mitochondria (110 vs. 37). Most genes are involved in photosynthesis. Corn has 20-40 chloroplasts per cell, with each chloroplast having 20-40 chromosomes (can make up 15% of DNA)

9. Endosymbiotic hypothesis: Free living prokaryotes ancestors of chloroplasts and mitochondria invaded plant and animal cells but provide useful function and so a symbiotic relationship developed over time. Differences in sexes: The transmission of cytoplasm differs between sex cells : – Male contribution: Sperm or pollen transfer little or no cytoplasm to the egg – Female contribution: Egg contributes almost all of the cytoplasm to the zygote

10. Maternal Inheritance: Maternal inheritance - the female phenotype in a cross is always expressed in its offspring Explanation: • Is a result of the expression of a gene found in the genome of an organelle • For most species, all of the organelle DNA that is found in an embryo is from the female. • This is the biological basis of maternal inheritance . Infectious Heredity: A parasite living in the cytoplasm is passed onto the offspring through the mother (maternal inheritance } Cause=Sigma (A virus found in the cytoplasm.)

11. Organelle chromosomes: A zygote inherits its organelles from the cytoplasm of the egg Maternal Inheritance: The patterns of inheritance is not associated with meiosis or mitosis because the organelles are in the cytoplasm not in the nucleus. Organelles have circular chromosomes.

12. Maternal Inheritance: Experiments were performed by Correns on the four o'clock plant • The plant has green, variegated (white and green) or white leaves • Normal flowers develop at different locations on the plant • Crosses were made among the flowers associated with each leaf color (results in table below) Female Male Progeny phenotype Green Green, Variegated or White Green Variegated Green, Variegated or white Variegated White Green, Variegated or White White

13. Maternal Inheritance: Results: The progeny cross always exhibited the color of the leaf of the female Trait expresses the maternal inheritance.

14. Extranuclear inheritance: “Transmission of genes that occur outside the nucleus found in most eukaryotes and is commonly known to occur in cytoplasmic organelles such as mitochondria and chloroplasts from cellular parasites like viruses or bacteria .” Types of Extranuclear inheritance: Vegetative segregatio n Uniparental inheritance Biparental inheritance

15. Vegetative segregation: Vegetative segregation results from random replication and partitioning of cytoplasmic organelles as with chloroplasts and mitochondria during mitotic cell divisions and results in daughter cells that contain a random sample of the parent cell’s organelles e.g . mitochondria of a sexually replicating yeast cells.

16. Uniparental Inheritance: Occurs in Extranuclear genes when only one parent contributes organelles DNA to the offspring e.g . Uniparental gene transmission is the maternal inheritance of human mitochondria at fertilization via the egg . The father’s mitochondrial genes are not transmitted to the offspring via the sperm . Chloroplast genes can also inherit Uniparentally during sexual reproduction. The mechanisms of Uniparental inheritance from species to species differ greatly and are quite complicated. For instance, chloroplasts have been found to exhibit maternal, paternal and Biparental modes even within the same species.

17. Biparental Inheritance: Occurs in Extranuclear genes when both parents contribute organelle DNA to the offspring . It may be less common than Uniparental Extranuclear inheritance, and usually occurs in a permissible species only a fraction of the time. An example of Biparental mitochondrial inheritance is in the yeast. When two haploid cells of opposite mating type fuse they can both contribute mitochondria to the resulting diploid offspring.

18. Cytoplasmic Inheritance examples… Killer particles in paramecium: These were identified by T.M sonneborn and his associates. Some races of paramecium aurelia produce a substance that has lethal effect on members of other races Such species were “killers” and particles responsible were “kappa” particles. These particles contain DNA, RNA, & protein. There are two types of kappa particles: Replicating form Killer form These particles produce substance called “paramecin”. These particles though inherited from cytoplasm, the maintenance depends on presence of gene “k” in nucleus.

19. Cytoplasmic Inheritance examples… Coiling in snails(predetermination ): Water snail Limnaea - some species where shell coils to right (dextral) and some other where shell coils to left (sinistral). Few species show both, where the mothers control it. Dextral is dominant to sinistral.

20. Cytoplasmic Inheritance examples… Milk factors in Mice: J.J Bittner identified extra nuclear factors controlling susceptibility of mice to mammary cancer. It behave like virus & transmitted through milk of mother to young mice. Mice receiving from mother were more susceptible than those which were fed from foster mother whose milk did not have these factors. This factor is transmitted through milk &other body fluids as saliva & semen. Totally mothers nourish the ebmryo for several months before birth & can exert some influence on young one. Phenocopy- environmentally induced change.

21. Cytoplasmic Inheritance examples… Male sterility in plants: This type is due to pollen failure. Rhodes MM found this in Maize. It persists after subsequent crossing s with fertile lines, which indicates maternal inheritance. It is attributed to cytoplasmic plasma genes transmitted by female gametes. This is useful in plants.

22. Cytoplasmic Inheritance examples… CO 2 sensitivity in dropsophila: L Heritier & Tessier found some true breeding dropsophila to be sensitive to CO 2 Dropsophila are generally insensitive to CO2, but when exposed become uncoordinated with legs paralysed. A particle “genoids” or “sigma” has been identified in the cytoplasm of somatic & reproductive cells of sensitive files. Genoids are transmitted through egg cytoplasm, sometimes through sperms also. It behaves like virus & has properties of plasma gene but non chromosomal.

23. Significance of cytoplasmic inheritance… Development of cytoplasmic male sterility several crop plants like maize. Pearl millet, sorghum, cotton etc. 2. Role of mitochondria in the manifestation of heterosis. 3. Mutation of chloroplast DNA and mitochondrial DNA leads to generation of new variation.

24. Quantitative Inheritance: “The process in which the additive action of numerous genes results in a trait.” Examples: Height Weight IQ Growth rate in farm animals. In addition to quantitative inheritance, inheritance of these traits is often referred to as "cumulative gene action" or " polygenic-inheritance” Some features show continuous variation & some show discontinuous variation.

25. Continuous variation: Human height is an example of continuous variation. Height ranges from shortest to tallest person. A characteristic that changes gradually over a range of values show continuous variation. e.g. Height Weight Foot length

26. Continuous variation:

27. Discontinuous variation: Human blood group is an example of discontinuous variation. A characteristic with only a limited value show discontinuous variation. e.g. Gender( male or female) Blood group(A, B, AB, O) Eye color

28. Discontinuous variation:

29. Quantitative Inheritance: “Genetic inheritance of a character (as human skin color) controlled by polygenes with each allelic pair of genes at a given locus having a specific quantitative effect .” Introduction to quantitative genetics: Quantification of the correspondence between phenotypic and genotypic values. Quantitative geneticists are often focused on partitioning the phenotypic variance into genetic and non genetic components . Classical quantitative genetics started with a simple model: Phenotype = Genetic Value + Environmental Effects

30. Partitioning of phenotypic & genotypic variance… “Phenotype is an organism's expressed physical traits.” It is determined by an individual's genotype and expressed genes, random genetic variation, and environmental influences . Examples: Examples of an organism's phenotype include traits such as color, height, size, shape and behavior . Phenotypes indicated in the pea pod images to the right include pod color, pod shape , pod size, seed color , seed shape, and seed size.

31. Partitioning of phenotypic & genotypic variance… Genotype is the genetic makeup, as distinguished from the physical appearance, of an organism or a group of organisms. Examples: • The gene responsible for eye color. • The gene responsible for hair color. • The gene responsible for height.

32. Multiple factor hypothesis… Two or more different pairs of alleles ,with presumed cumulative effect, govern the quantitative traits . those alleles which contribute to the trait involved are called contributing , effective or active alleles; those alleles which do not appear to do so are non-contributing non- effective, null alleles . A gene, individually exerting a slight effect on the phenotype is called polygene. sine there are usually many genes of this kind for one quantitative trait is called multiple factor hypothesis.

33. Qualitative Genetics Quantitative Genetics Characters of kind. Characters of degree. Discontinuous variation; distinct Continuous variation Single gene effects. Polygenic control; effects of single genes too slight to be detected. Concerned with individuals mating & progeny. Concerned with population of organisms consisting all kind of mating. Analyzed by making counts and ratios. Statistical analyses give estimate of population parameters such as mean & standard deviation. Example: round or wrinkled seed of peas Example: skin color in man.

34. Polygenic Inheritance: A polygenic trait is one whose phenotype is influenced by more than one gene. Traits that display a continuous distribution, such as height or skin color, are polygenic. The inheritance of polygenic traits does not show the phenotypic ratios characteristic of Mendelian inheritance . E ach of the genes contributing to the trait is inherited. Many polygenic traits are also influenced by the environment and are called multifactorial.

35. Trangressive variation: The appearance, in a segregating generation, of individuals showing expression of a trait outside the extremes defined by the parent of the cross that was used to generate the population. Example: In a cross between a large golden Hamburg chicken and small Sebright bantam variety, the F progeny was intermediate between the two parents as could be expected in a polygene system . But surprisingly in the F2 generation (obtained by a cross between F, individuals) some of the birds were either larger than the golden Hamburg parent or (some) were smaller than the Sebright bantam parent.

36. Modifying Genes: A gene that alters or influences the expression function of another gene including the suppression or reduction of the usual function of the modified gene . Also called modification allele . Example: Mice homozygous for the recessive mutation piebald exhibit a white-spotted coat caused by the defective development of neural crest-derived melanocytes. severity of white spotting varies greatly, depending on the genetic background on which s is expressed. A backcross between two inbred strains of s/s mice that exhibit large differences in the degree of spotting was used to identify six genetic modifiers of piebald spotting on chromosomes 2, 5, 7, 8, 10, and 13.

37. Modifying Genes : The loci differed in their spatial contribution to spotting on the dorsal versus ventral surfaces of mice. non additive interactions were observed between loci on chromosomes 2 and 5. This study underscores the power of using genetic analyses to identify and analyze loci involved in modifying the severity of phenotypic traits in mice.

38. Examples of polygenetic inheritance… Kernel color in wheat: There are two genes which control wheat kernel color. The phenotypes will vary from a dark red color to a light tan color (called white) . The darkest kernels are produced from a plant that has 4 dominant alleles. The lightest kernels are produced from a plant that has 4 recessive alleles. Intermediate color are produced from having 3 or 2 dominant alleles

39. Examples of polygenetic inheritance… These categories are listed from darkest to lightest in color . Dark Red Medium Red Light Red/White Medium White White

40. Examples of polygenetic inheritance… Skin color in human: C.B . Davenport reported the inheritance of skin color in negro and white populations in U.S.A In U.S.A. the populations derived from marriages between negro and white individuals are known as mulattoes. The offspring from negro-white marriages give intermediate skin color in the first generation. When such individuals intermarry among themselves, all shades of skin colour are obtained. If two loci A and B are responsible for the skin colour, negroes can be represented by the genotype AABB and whites as aabb. Mulattoes will be AaBb with intermediate skin color.

41. Examples of polygenetic inheritance…

42. Examples of polygenetic inheritance… Eye color in Men: In human beings , the colour of eye is found to be determined by polygenes . T hese genes have been suggested by polygenes . T hese genes have been suggested to be x-linked . At least 9 lasses of eye colour are seen in humans . I n order of increasing amount of melanin pigmentation , these colors can be designated as light blue , medium blue , dark blue ,gray, hazel, green, light brown , medium brown & dark brown.