X.Extra-nuclear.ppt

7/27/2019 X.Extra-nuclear.ppt

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VIII. Extranuclear Inheritance(Extra-chromosomal inheritance

organelle heredity

cytoplamsic inheritance)

It involves DNA in mitochondria or chloroplast.


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The genes in mitochondria or chloroplasts are

transmitted with cytoplasm of germ cells.

Transmission is often from mother to children,

because during gamete formation, the functionalegg contains large amount of cytoplasm.

Cytoplasmic inheritance often involves genetic

materials carried by mitochondria - organelle

heredity.


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DNA on mitochondria is a circular structurecalled mtDNA.

Human mtDNA contains 16569 base pairs and

holds 37 genes.


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Because most of mitochondria DNA products are

related with energy production, any mutation cancause serious consequence.

For Exp., Kerns-Sayre Syndrom (KSS)

Disorder in hearing, vision and heart.

Multiple deletion mutation of mtDNA at different

locations.

Female eggs normally contain many mitochondria.

Sperms only have a few.


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Infectious Inheritance:

Some infectious agents can be inherited

through cytoplasmic inheritance.


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Occasionally, a virus can infect a host cell and

replicate in host cytoplasm for several generations.

Such virus can be passed through ooplasm to

progeny cells or offspring and display an altered

phenotype.

For Exp. A cancerous RNA virus can infect

oocytes Also, HVB can be maternally inherited.

HIV?


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Maternal effect

The maternal genotype has a strong influence onthe early embryo development.

Some genes of the female gamete can betranscribed and the gene products present in the

ooplasm. Following fertilization, these proteins

influence the early embryonic development.

Mutations in these genes can have lethal effect on

embryo development.


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Gene Imprinting or Genomic Imprinting

(p191 Concept close up)

Human tumor in the inner ear is inherited in a

paternal way.

The gene is autosomal, both sexes can carry it.

Which parent gives the gene is an important

factor.


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Only when it is carried on father's chromosome,

the gene would be expressed. When the gene ispassed by the mother, it is blocked by some kind

of inhibition - gene imprinting.

DNA methylation is possible mechanism for

gene imprinting.

Gene imprinting is an event where DNAmethylation inactivates certain genes.


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Another human example: Huntington disease,

caused by a dominant allele.If father provided it, early onset;

If mother provided it, later onset

Imprinting is not a permanent event. An allele that

is inactivated in one generation can be an active

allele in the next generation.

X.Extra-nuclear.ppt

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