1. The document discusses various examples of extra-chromosomal or cytoplasmic inheritance, including chloroplast mutations in four o'clock plants causing leaf variegation, mitochondrial mutations in yeast, and maternal effects on shell coiling in snails.
2. It also describes infective heredity through kappa particles transmitted cytoplasmically in Paramecium. The kappa particles can kill sensitive Paramecium strains and are transmitted from parent to offspring depending on nuclear genes.
3. Cytoplasmic inheritance involves transmission of hereditary material like genes located in organelles like chloroplasts and mitochondria, rather than in the cell nucleus, and can be purely maternal.
3. The Mendelian inheritance pattern mostly advocates the
characters transmittance from parents to offspring via the
gametes and the later on this has been confirmed by the courtesy
of the chromosomes present in the nucleus. But in due course,
evidence of the transmission of characters was explored by
Correns while the investigation of characters in Mirabilis jalapa
and later on by Baur in Pelargonium zonale. They termed this
inheritance pattern as Plastid inheritance. Later on, a number of
geneticists like Rhoades, Sonneborn, Ruth Sager and Rs & Plaut
also demonstrated this type of inheritance pattern on the different
other experimental materials. This is now defined as cytoplasmic
inheritance pattern .In this consequences, the character of only
one of the two parents( usually the female one) is transmitted to
the progeny. As a result, reciprocal crosses exhibit consistent
differences for such characters and there is lack of segregation of
traits in the subsequent generations.
4. Genes in the chromosomes have undoubtedly been proved to be
responsible for the transmission of the various hereditary
characters which in turn are located in the nucleus. But in recent
years , there have been found some evidences which suggest that
inheritance of characters occur by some self-perpetuating or
replicating bodies like plastids and mitochondria which possess
their own equipment for synthesizing for DNA and proteins
present in the cytoplasm and not in the chromosomes present in
the nucleus. This particular type of mechanism in which
cytoplasmic particles or inclusions take part in transmission of
characters from generation to generation constitutes cytoplasmic
inheritance. The total self reproducing hereditary material of
cytoplasm is termed as Plasmon like the genome (which refers to
the total gene complement of an haploid set of chromosomes) of
chromosomes and such units of cytoplasmic hereditary material
are called cytoplasmic genes or plasma-genes or Plasmons.
5. The cytoplasmic hereditary units are denoted by Greek letters-
alpha, beta, gamma, sigma and so on, in contrast to the
chromosomal genes which are denoted by Roman letters- a, b, c,
d and so on. While considering various examples of cytoplasmic
inheritance it has been assumed that the cytoplasm in the sperm
cell is present in very minute quantity and mostly it is in larger
quantity in the egg. So, we could expect that plasma-genes
mostly will transmit only through the egg cytoplasm rather than
minute sperm. Thus, plasma-genes for various sizes and
characters are likely to be supposed only in the egg cytoplasm.
(i) It is more or less maternal inheritance i.e., only female
contribute towards inheritance and therefore.
(ii) The result of reciprocal crosses are not the same. In these
features, extra-nuclear inheritance contrasts sharply from nuclear
inheritance. Only in few cases, mostly in plants, evidences have
been found that some traits or characters are transmitted through
cytoplasm. Such traits are transmitted through the female line
only. Each set of nuclear genes is sometimes
6. designated as genome and all the hereditary materials transmitted
through the cytoplasm is referred to as plasma-genes, cytoplasmic
genes, cytogeneses, extra nuclear genes or extra chromosomal
genes.
MATERNAL EFFECTS: The development of some characters in
several organisms is either governed or markedly influenced by
the genotype of the parent-known as maternal effects. Such
characters, are governed by nuclear genes. But due to maternal
effect, they show the following features:
1. Reciprocal differences in F1,
2. Which, in most cases , disappear in F2;
3. A considerable smaller variation in F2 as compared to that in
F3. In some extreme cases, there may be no segregation in F2.
In such cases, phenotypic segregation is evident only in F3
gebneration.Many important characters of both plants and
animals show maternal effects , of which some of the examples
are stated below for strengthening this biological uniqueness.
8. CHLOROPLAST INHERITANCE
Inheritance of plastid character due to plasmagenes located in
the plastid is known as plastid inheritance. Most of the studies
in this regard basically based on the studies of chlorophyll
variegation in leaves but recent studies based on RFLP and
SEM are extensively used to explore this thought. Variegation
refers to the presence of white or yellow spots on the variable
size on the green background of leaves. Mutant plasmagenes
affecting chloroplasts are found in the different cultivated
plants like barley, wheat, maize, pea, tobacco and many other
ornamental plants of economic importance. The present study
has been done on the leaves of four o’ clock plant either green ,
white or variegated leaves as stated below and this can confirm
the maternal inheritance to support the concept of plasmagenes.
9. Findings of Correns In Mirabilis jalapa
Leaf phenotype of the
branch used as Female
Leaf phenotype of the
branch used as male
Leaf phenotype of the
F1 progeny
Green Green Green
Do White Green
Do Variegated Green
White Green White
Do White White
Do Variegated White
Variegated Green Green. White &
variegated in variable
ratios in each of the case
Do White
do Variegated
10. EXPLANATION
Let us pay a glance to the previous table to explore the beauty
of the transmission of the leaf phenotype of the plant, Mirabilis
jalapa as observed by Correns. He made reciprocal crosses in
all possible combinations among the flowers of these three
types of branches.
1.When the flowers from the green branch used as female , all
the progeny were green irrespective of the phenotype of the
male parent.
2. Similarly, when the flowers from the white branch used as
female, all the progeny were white irrespective of the
phenotype of the male parent.
3. In the third consequences, the female variegated branches
determine the phenotype of the F1 irrespective of the male
parent phenotype. But in the progeny from the different crosses
involving flowers from variegated branches as the female
parent , green, white and variegated plants were recovered.
11. OBSERVATION & COMMENT
The results confirm the plasmagene directs the color
combination of the leaf of the aforesaid plant. Proplastids
generally produce the plastids. Proplastid having mutant
plasmagene differentiate into colorless abnormal plastids while
the normal allele develop normal plastid. The maternal
transmission of plasmagenes in higher plants can be explained
on the basis of unequal contribution of male and female
gametes to the cytoplasm of zygote. As per the biological
mechanisms of the sexual reproduction, egg cell has a
considerable amount of cytoplasm having several mitochondria
and proplastids while the male counterparts bear seldom
existence of the two organelles. Several mechanisms operated
by in vitro techniques of the cell fusions confirms the
Proplastid origin from female not male. This is the beauty of
the cytoplasmic inheritance from female counterpart.
13. Mitochondria, most important cell organelles deserve mentioning
as it is the power house of cell & store house of energy along with
its uniqueness as far as the self replicating nature due to the
presence of self DNA for its replication. It is originates from
preexisting mitochondria and it bears many plasmagenes in mt-
DNA. The information extracted from experiments confirmed that
mitochondria from only of the parents are transmitted to the
progeny. Therefore, characters controlled by the genes located in
mt-DNA shows cytoplasmic inheritance. Cytoplasmic Male
sterility (CMS) in different crops like maize, jowar, bajra are
some of the typical examples in this regard. Mitochondrial
inheritance in Yeast can enough to explain the inheritance of
characters in this regard as stated below. Mitochondrial genome in
Yeast varies in different strains up to 10000 bp in their genome
size . Extensive deletions can occur in mtDNA , in case of petite
mutants. All petite mutants lack mitochondrial function as it can
grow anaerobic ally but it may be lethal particularly for the
aerobic plants and animals.
14. All the petite mutants lack mitochondrial function and they are of
three types.
1. Nuclear petites- Produced by nuclear gene mutation and they
abolish mitochondrial function and follow Mendelian
inheritance,
2. Neutral Petites- Characterized by the absence of mtDNA ,
represent an extreme situation and are recessive in inheritance,
3. Suppressive petites- These mutants have much smaller
mtDNAs, complexity of their genome ranging from 0.2% to
36% of the normal genome. These petite may contain any
sequence of mtDNA and these copies may present as separate
circles, or as a multimeric molecule in which the copies are
arranged in tandem as direct or inverted repeats. some of the
petites are stable while others are unstable and further
rearrangements of their sequence occur.
When a suppressive or rho petite is crossed with a wild strain, in
certain portion of the petite is found and the wild DNA
15. The proportion of the progeny in which suppression occur
constitutes the degree of suppressiveness. The cause of the
suppression is highly suppressive petites is a preferential
replication of the petite genome. This may be due to presence of
a greater concentration of origin-like sequences called rep
regions, in petite mtDNA than in a wild type mtDNAs. Yeast
mtDNA has specific sequences involved in the replication
initiation but petite mtDNAs lacking this sequence . This
indicates that all segments of mtDNA in yeast can be
independently replicated since any sequence of mtDNA can be
present in a petite.
Not pnly in Yeast, mitochondria and its mutation in mtDNa has
very significant role in higher animals like human beings .
Leber’s Hereditary Optic Neuropathy( LHON), a sudden lost
blindness in adults is associated with the mutation of mtDNA
caused optic nerve death and it’s a consequence of maternal
transmission. Pearson Marrow-Pancreas syndrome is also caused
by this type of mtDNA mutation in humans.
18. Your heart is mostly in the left side while your liver is on the
right side. How does it happen ? Do the reverse situation
happen ? If you look at snail’s shell , the chances are of
coiling is at the right direction but very often you can find an
unlucky one that twists in the opposite direction. The chilarity
of snail shells is an outward manifestation of left-right
asymmetry and this has been explored with the help of the
maternal effects of the inheritance pattern as experienced by
the biological world as far as the inheritance of characters
pattern in the long passage of evolution. An extreme example
of this kind of maternal effects is known in the snail,
Limnaea. In this snail, the direction of the coiling of its shell
is controlled by a single gene D/d. The dominant allele D
produces roght-hande4d (=dextral) coiling while its recessive
allele d produces left handed (=sinestral) coiling . The
direction of shell coiling in an individual is governed by the
genotype of the female parent and not by own genotype.
19. One of the classical examples of intricate relationship between
maternal genotype and egg cytoplasm “phenotype” was studied
in snails by Sturtevant. He showed that there are two strains of
water snails (limnaea peregra) that differ each other in the
direction of coiling of shell.
Looking into the opening of the shell it can be seen that in one
strain the shell always coils to the left (sinistral) whereas in the
other strain the shell always coils to the right (dextral). In the
cross dextral ♀x sinistral ♂ all the F, progeny have dextial coils
implying that dextral is dominant over sinistral. However, in the
F1, x F1, cross (i.e., inbreeding), all the F1 snails are also dextral.
The reciprocal cross (dextral ♂ x sinistral ♀) produces F1,
progeny that are all left coiler. In this case F1, x F1, cross also
yields only dextral coils.
From these experiments it becomes clear that coiling of snails is
not determined by individuals’ own genes but by those of mother.
22. As stated earlier, there are three distinct classes of non-
Mendelian inheritance:
1. Inheritance of structure and patterns,
2. Inheritance due to parasites, symbionts and viruses,
3. Cytoplasmic inheritance.
A number of cases were once regarded as classical cases of
cytoplasmic inheritance but actually they are due to the
presence of parasites, symbionts and viruses. The Kappa
particles of Paramecium is one of the most interesting
episodes deserve mentioning in this regard to explore the
beauty of the biology of inheritance as stated below.
Paramecium is a unicellular. Eukaryotic ciliates widespread in
fresh water and the body is covered with ciliates, contains
two nuclei-micronuclei and macronuclei and possess
intracellular bacteria called kappa particles that bear huge
significance in this regard.
23. Sonneborn and his associates have explored the transmission of
cytoplasmic particles and their relation to nuclear genes in
Paramecium infusoria in 1943. Strains of P. aurelia can harbor
some 10 different Gram(-) bacteria species in cytoplasm, the best
known being called kappa particles. Maintenance of each
bacterial species requires a particular nuclear genes of the host
paramecium. The bacteria may be transferred from one to other
cell by conjugation. Certain strains are known as killer strains,
secrete into the water in which they live , a toxic substance
paramecin which injures and kills individual of the sensitive
strains of the same species. Killer strains contain in cytoplasm
large amounts of DNA particles which are called Kappa particles.
Kappa particles are called either- bright or non-bright depending
upon their appearance under the light microscope. Bright one are
believed to produce the toxin. All Paramecium cells lacking
kappa are sensitive to paramecin. Bright kappa is a symbionts
living in the cytoplasm of Paramecium and the normal
component of Paramecium cells.
24. Kappa particles show cytoplasmic transmission like plasmagenes.
Generally , there is no cytoplasmic exchange accompanying the
exchange of nuclei during conjugation in Paramecium. Therefore
, during conjugation between one killer and one sensitive
Paramecium, the sensitive cell does not receive any kappa
particles. As a consequence, the sensitive cell remains sensitive
after the conjugation and produces sensitive progeny. But
occasionally, cytoplasmic exchange does occur during
conjugation; in such cases, both animals that participated in
conjugation (exconjugants) receive kappa. But subsequent
propagation of kappa depends on their nuclear genotypes of these
animals. Kappa particles , like other bacteria , multiply through
fission. However kappa particles are able to multiply only in
animals having genotypes KK or Kk. In kk animals, kappa are
unable to multiply. As a result, they are eliminated from such
animals. The killer animals with kk genotype ultimately become
sensitive due to loss of their kappa particles.
26. We have learned the meaning of cytoplasmic inheritance.
Cytoplasmic DNA is found in certain cell organelles and can be
passed onto offspring strictly from the female, male, or a mixture
of both parents. Cytoplasmic inheritance examples are Iojap in
maize, pokiness in Neurospora, Oenothera, etc. There are two
types of cytoplasmic inheritance-Plastid and mitochondrial
inheritance. Cytoplasmic inheritance is useful in many ways such
as in explaining the role of various cytoplasmic organelles in the
transmission of characters, facilitating the production of hybrid
seeds, and many more. Mendel for the first time tried to explore
the cause and consequences of the characters of biological entities
along with their mode of transmission. He proposed the three set
of principles in this regard and this kind of transmission was
recognized as the nuclear transmission but Mendel never thought
about the contribution of cytoplasm in characters transmission and
he did not initially thought about the maternal effects in characters
transmission. But post-Mendelian research offered a recipe of
thought in this regard and it becomes an awesome ingredients.
27. References:
1. Google for images,
2. Principles of Genetics- Basu & Hossain,
3. A textbook of Botany (Vol III) Ghosh, Bhattacharya,
Hait
4. Fundamentals of Genetics- B.D. Singh,
5.A Textbook of genetics- Ajoy Paul
DISCLAIMER:
This presentation has been made to enrich open source of
information without any financial interest. The presenter
acknowledges Google for images and other open sources
of knowledge to develop this PPT.