cytoplasmicinheritence-200703130538 (1).pdf

In 1950 Dr. Sangers and his colleagues suggested the possible role of cytoplasm in
certain cases of inheritance .
Example – in Chlamydomonas inheritance of certain characters is controlled by the
non-chromosomal genes.
• The cytoplasm in such cases contains self-perpetuating hereditary particles
formed of DNA. These may be mitochondria, plastids or foreign organisms etc.
• The total self-duplicating hereditary material of cytoplasm is called plasmon and
the cytoplasm units of inheritance are described as plasmagenes.
• Plasmagenes are located in DNA present in mitochondria and in chloroplast.

1. CYTOPLASMIC INHERITANCE
OR
EXTRACHROMOSOMAL
INHERITANCE

2. INTRODUCTION
•In 1950 Dr. Sangers and his colleagues suggested the possible role of cytoplasm in
certain cases of inheritance .
Example –in Chlamydomonas inheritance of certain characters is controlled by the
non-chromosomal genes.
•The cytoplasm in such cases contains self-perpetuating hereditary particles
formed of DNA. These may be mitochondria, plastids or foreign organisms etc.
•The total self-duplicating hereditary material of cytoplasm is called plasmon and
the cytoplasm units of inheritance are described as plasmagenes.
•Plasmagenesare located in DNA present in mitochondria and in chloroplast.

3. Total hereditary material
Plasmon( all hereditary
material in
cytoplasm)extra
chromosomal
Plastogenes( in plastid)
Kinetogenes(in
kinetosome)
Chondriogene(in
mitochondria)
Centriogenes(centrioles)
Genome(all hereditary
material in nucleus)
genes
Types of hereditary material in living
organisms

4. The crosses exhibiting following types of results
may suggest extrachromosomal inheritance:-
Differences in
reciprocalcross
results
Maternal
influence
Infection like
transmission
Indifference to
nuclear
substitution
Inconsistent with
theSegregation
and non Mendelian
segregation

5. Criteria for cytoplasmic inheritance
The cases of cytoplasmic inheritance are found to exhibit maternal influence.
There is very little cytoplasm is contained in sperm and most of the
cytoplasm is contributedto the zygoteby ovum or egg.
Hence, if there are hereditary units in the cytoplasm, these willbe
transmitted to the offspring through the egg.
The offspring, therefore, will exhibitmaternal influence.

6. Three types of cytoplasmic inheritance
Maternal inheritance
Organellar inheritance
Inheritance involving infectious
particles

7. Examples of Maternal inheritance
1. Maternal influence on Shell Coiling in Snail Limnaea:
•Snail exhibit two types of coiling of their shell:
Dextral coiling
•The shells coiled towards right.
Dominant (D)
Sinistral coiling
•Those coiled towards left.
RECESSIVE (d)

8. The experiment of Boycott, Diver and Gastric and explanation given by Sturtevant
indicate that the character of coiling is determined by the gene of the mother and
not by the individual's own gene.
If a dextral female is crossed with
sinistral male, all the F1 Snails possess
dextral shell. Surprisingly even in F2
also all the offspring possess dextral
shell irrespective of the fact that a
few of them possessed recessive
genes and were supposed to develop
sinistral coiling.
In areciprocal cross between sinistral
female and dextral male, and the F1
offspringwhich according to their
genotype were supposed to be
dextral, were found to develop
sinistral shell coiling and in
F2generation all the offspring
developed dextral coiling.

9. Abnormal observations ofreciprocal crosses
•Some of the snails which are homozygous for sinistralcoiling have
dextral coiling similar to the mother.
•Some of the snailswhich havegene for dextral character display
sinsitralcoiling like the mother.
It clearly indicates that maternal genotype through her egg
cytoplasm dictates the shell coiling of the offspring.

11. Inheritance involving infective
particles
In some cases, cytoplasmic inheritance is associated
with infective particles, like parasite, symbiotic or
viruses which are present in the cytoplasmic of an
organism.
There are cases, where cytoplasmic inheritancedepends
on extrachromosomal particles which are not essential
for cell function and thereforemay be presentor absent.
Such, dispensableparticles are not only inherited but are
also infective, since they canbe introduced into new
hosts without the need of actual process of reproduction.

12. Kappa particles in Paramecium
•Sonneborn(1943) described the inheritance of some cytoplasmic
particles known as kappa and their relation to nuclear gene in
Paramecium.
•There are two strainsof Paramecium
•The killer secretes a toxic substance
Called paramecinwhich kills the sensitive.
•The paramecinofkiller strain contain large number of kappa
particles in their cytoplasm.
•The product ofkappa particles is dependent on a dominant allele K,
that killer strains areKK or Kk and sensitive strains are ordinarily
kk.
Killersensitive

15. Breasttumour In Mice
•The mammary cancer in mice has been found to be
maternally transmitted.
•Studied byBitiner
•Whenfemales mice crossed with normal maleswithout
cancer susceptibility almost 90% of the
offspringdeveloped breast cancer.
•When males from this tumour susceptible strain were
mated to normal females all the offspringwere normal.
•These results are suggestive of cytoplasmic inheritance.

17. Organellar
inheritance
•The true cytoplasmic inheritance is one
which involves plastids (chloroplast) and
mitochindria.
•Thus cytoplasmic inheritance is again of two
types:
1.Plastid inheritance
2Mitochondriainheritance
•The cytoplasmic inheritance is governed by
genes which are found in chloroplast and
mitochondria.
•The genes whichgoverncytoplasmic
inheritance arecallled palsma genesor
cytoplasmic genes or cytogene or
extranuclear genes.

18. Leaf varigation in Mirabilis
jalapa
•The conclusive evidence for cytoplasmic inheritance was first
presented by Carl Correns in Mirabilis jalapa (four 'o' clock palnt) in
1909.
•He studiedinheritanceof leaf varigation in M. jalapa.
•Varigation refers to the presence ofwhite or yellow spote of
variable sizeon the greenbackgroundof leaves.
•In M. jalapa, leaves may be green, white or varigated. Some
branches mat have only green, onlywhite and only varigated
leaves.
•Correns made crosses in allpossible combinations amongthe
flowersproduced on these three types of branches.

19. •Flowers on wholly green branches produce
seeds that grow intonormalplants.
•Flowers on varigated branchesyield offspring of threekinds
green, white and variegatedin variable proportions.
•Flowersfrom brancheswholly white produces seeds
thatgrow into whiteplantsthatis withoutchlorophyll.

22. Cytoplasmic
male sterility
The inheritance of some characters is governed by
mitochondrial DNA. The examples of mitochondrial inheritance
include cytoplasmic male sterility in plants, pokyness in
Neurospora, petite in yeast etc.
The cytoplasmic male sterility is controlled by plasma genes
associated with mtDNA ir cpDNA.
In other words, in maize cytoplasmic sterility is governed by
mitochondrial DNA. Cytoplasmic sterilityis found in several
othercrop plants, pearl millet,Sorghum, cotton, etc.
In certain other cases, althoughmale sterility is
whollycontrolledby cytoplasm, but a restorer gene if present in
thenucleus will restore fertility.

23. •For instance , if female parent is male sterile,
then genotype (nucleus) of male parent will
determine the phenotype ofF1 progeny.
•The male sterile female parent will have the
recessive genotype (rr) with respect to restore
gene. If male parent is RR, F1 progeny would be
fertile (Rr).
•On the other hand , if maleparents is rr , the
progenywould bemale sterile.
•If F1individual (Rr) is testcrossed , 50% fertile
and 50%male sterile progeny would be
obtained.

24. Inheritance of genetic
Male sterility in plants
25% 50% 25%

25. Significance
•Cytoplasmic inheritance has been useful in explaining the role of various
cytoplasmic organelles in the transmission of characters in different organisms.
•Studiesof cytoplasmic inheritance have played key role in mapping of
chloroplast and mitochondrial genome in several speciesexampleyeast,
Chlamydomonas, maize, human etc.
•The CMS cytoplasm can be easily transferred to various agronomic bases for
their usein the developmentof superior hybrids. Since CMS based hybrids
havedanger of uniformity, it isdescribe to utilize variousCMS sources.
•Role of mitochondria in the manifestation of heterosis is gaining
increasingimportance these days.

26. THANKS