Cytoplasmic Inheritance:
Imagine genetic information passing from a mother to her child. It happens through tiny structures called organelles in the cell.
These organelles have their own set of instructions, separate from the cell’s nucleus.
Why is this important? Because it affects how traits are inherited!
Genomic Imprinting:
Think of it like a “parental tag” on genes. Some genes behave differently depending on whether they come from the mother or the father.
Epigenetics plays a role here—it’s like a switch that can turn genes on or off.
This process affects development and can lead to certain diseases.
Remember, these concepts help scientists understand how our genes work and why we’re unique! 🧬
Introduction
Maternal Inheritance
Organellar inheritance
Mitochondrial inheritance
Chloroplast inheritance
Inheritance involving kappa particle
INTRODUCTION
DNA or RNA is the Genetic materials carrying information from
one generation to another.
Besides these two nucleic acids the cytoplasm also
contributes to the inheritance of some characters in some
organisms.
Extra chromosomal inheritance is also defined as nonmendelian inheritance
Inheritance due to genes located in cytoplasm plasmagenes.
The genes are located in DNA present in mitochondria and in chloroplasts these
are called organellar genes. This type of inheritance is also called as
cytoplasmic inheritance.
The evidence of cytoplasmic inheritance was first presented by Carl Correns in
mirabilis jalapa.
In 1943, Sonnenborn discovered Kappa Particles in Paramecium and they are
inherited through cytoplasm.
In cytoplasmic inheritance the character of female parent is only transmitted to
the progeny
MATERNAL INHERITANCE
The character of only one of the two parents (usually female parent) is
transmitted to their progeny.
It is usually referred to as extra-chromosomal or maternal or uniparental
inheritance.
The transmission of cytoplasm differs between sex cells:
Sperm or pollen transfer little or no cytoplasm to the zygote, but Egg
Contributes almost all of the cytoplasm to the zygote
This pattern of mtDNA inheritance is well known as "maternal
inheritance.
ORGANELLAR INHERITANCE
The cytoplasmic organelles like plastids (chloroplast) and
mitochondria are involved.
The cytoplasmic inheritance is governed by the genes of
mitochondria and chloroplast.
The genes which involve in cytoplasmic inheritance are called
plasma genes or cytoplasmic genes or extra nuclear genes.
EXMAPLES FOR NON-MENDELIAN INHERITANCE
Plastid inheritance in Mirabilis
Kappa particles in Paramecium
Shell coiling in Snail
Cytoplasmic male sterility in Maize
Milk factor in mice
CHLOROPLAST INHERITANCE
LEAF VARIEGATION IN MIRABILIS JALAPA
The evidence for cytoplasmic inheritance was first presented by Carl
Correns in Mirabilis jalapa (Four ‘O’ clock plant).
He observed a strange pattern of inheritance and studied inheritance
of leaf variegation
In M. jalapa, leaves may be g
4. What is Cytoplasmic Inheritance?
It simply refers to the inheritance of traits that
are not controlled by nuclear genes
Instead they are determined by the
cytoplasm (or things in it, including
organelles)
The reasonable Cytoplasmic Genes
are located in specific organelles
{e.g. Chloroplast, Mitochondria}
It is also known as Non-Mendelian
Inheritance
5. Parental Contribution
Based on the parental cytoplasmic
contribution it is of two types -
Uniparental Inheritance:-
Where genetic material or traits are
inherited from a single parent (usually
mother) e.g. in humans, mtDNA is
inherited solely from the mother.
Biparental Inheritance:-
This can occur when there is a transfer
of extrachromosomal genetic material
from both the maternal and paternal
parents to the offspring. e.g. chloroplast
transmission in Pelargonium cultivars.
6. In 1909, Carl Correns reported some surprising result
from his study on four o’ clock plants (Mirabilis jalapa)
Maternal Inheritance
The blotchy leaves of these variegated plants
showed patches of green and white tissues.
But some branches carried only white and
some carried only green leaves.
They have been intercrossed in a variety of
different combinations by transferring pollen
from one flower to another
Carl Correns
8. How this results could be explained?
The difference in leaf color was
known to be due to presence of
either green or colorless chloroplast
These cytoplasmic organelles are
transmitted from the maternal side
but never from the pollen
The inheritance pattern might be
explained if these cytoplasmic
organelle are somehow genetically
autonomous
9. Chloroplast DNA
In 1962, the discovery that the chloroplast contains
ribosomes and performs protein synthesis revealed that
the chloroplast is genetically semi-autonomous
cpDNA is closed, circular and double stranded
Chloroplast genomes are 130-150kb
It has about 110 genes in it
Most genes are involved in Photosynthesis
This non-mendelian inheritance pattern was later traced to a gene named
iojap which codes for a protein required for proper assembly of the
chloroplast ribosome.
11. Organelle Heredity
The cytoplasmic organelles like plastids (chloroplast)
and mitochondria are involved in this type of
inheritance. It is governed by genes located in their-
cpDNA
mtDNA
Both the organelles have –
Their own ds circular DNA which lacks histone
70S ribosomes
Can move and reproduce in their own
Resembles bacteria
Endosymbiotic Theory
12. Mitochondrial Inheritance
in Human Disease
During fertilization sperm only contribute its
nucleus. Available mtDNA in zygote is that of
the mother. So if the egg contains mutant
mitochondria, children may have mitochondrial
disorder, like-
Leigh Syndrome:
Genetic mutation in mtDNA
Chronic lack of energy in the cells
Affects the central nervous system
Progressive degeneration of motor functions
Appears before age 2 and dies in most cases
13. Maternal Effect
There is no genetic influence of either the progeny or the
father in that character which shows such maternal effect.
Nuclear genotype of mother decides the phenotype of progeny.
In multicellular eukaryotes, maternal effect does not produce
the same result in reciprocal crosses.
This effect is often due to the mother supplying messenger
RNA or proteins to the egg.
It introduces the concept of phenotypic plasticity, an important
evolutionary concept
A maternal effect is a situation where the phenotype of an organism is
determined by the genotype of its mother in the early cleavage steps of
that progeny’s life
15. Rules of Extrachromosomal Inheritance
Extrachromosomal DNA does not follow the Mendelian pattern of inheritance
Ratios typical of Mendelian segregation are not found, because meiosis-based
Mendelian segregation is not involved.
The inheritance of extrachromosomal factors is independent of genes
located within the cell nucleus.
Extrachromosomal traits are inherited exclusively from the mother.
Phenotypic variation occurs easily.
Non-nuclear inheritance can occur in the cytoplasm of cells and involves
genes present in cytoplasmic organelles like mitochondria and plastids
16. Why are these Important?
Useful in explaining the role of various cytoplasmic organelles
in the transmission of characters
Facilitated the mapping of the chloroplast genome and
mitochondrial genome in numerous species
The evolution of organelle genomes is well understood
Used to study the evolution of sex determination mechanisms
in some species
Helped to study the diseases related to mutant mitochondria
Have opened the door to a new world of reproductive
medicine – “3 Parent Baby Technique”
18. History of Imprinting
in 1980s scientists tried to make embryos with only maternal DNA
(from two eggs) or only paternal DNA (from two sperm)
They found that these embryos did not develop normally and died early.
They also had different defects depending on which DNA they had.
This suggested that some genes were regulated differently depending
on whether they came from the mother or the father
19. Definition
Gene inactivation on selected chromosomal regions of autosomes is
called Genomic Imprinting.
This is the cause of preferential expression of one of the parental
allele.
Maternal imprinting refers to transcriptional silencing of the
maternal allele.
Paternal imprinting implies that the paternal allele is inactivated.
Imprinting occurs in the ovum or the sperm, before fertilization.
Mechanism of Genomic Imprinting can be explained by
EPIGENETICS
20. EPIGENETICS
Reversible heritable chemical modification of DNA or histone or nonhistone proteins
that does not alter DNA sequence itself is called EPIGENETICS
The term epigenetics means, above genetics' as the nucleotide sequence is unaltered
This is one of the recently discovered method of regulation of gene expression.
Epigenome: Constellation of covalent modification of DNA and histones that impact chromatin
structure and modulation of gene expression.
Epigenetic modifications include DNA Methylation, Post-translational modification of Histones.
21. DNA Methylation
It is usually restricted to Cytosine residues
in CpG dinucleotide of CpG islands
Enzyme responsible for methylation is
Methyl Transferases
Generally decreases the gene expression
It is a biological process that adds methyl groups to
DNA molecules and change the activity of a DNA
segment without changing the sequence
Gene promoters and regulation by methylation-
demethylations-
• Majority of gene promoters have high CG content.
• CpG islands are the common sites of methylation-
demethylations
⚫ Hence, methylation-demethylations plays an
important role in regulation of gene expression.
⚫ CpG islands of promoters are typically
unmethylated, it favors transcription.
25. Why studying Genomic Imprinting
is Important?
• It affects embryonic and fetal growth and
development
• It is related to the uterine resource extraction
and parental conflict
• It is essential for normal phenotypes and
diseases
• It can help us understand how other genes
bypass epigenetic reprogramming
• It involves different epigenetic processes (DNA
methylation and histone modifications)1
• It is controlled by imprinting control regions
(ICRs) that demonstrate differential DNA
methylation
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