Another Question on Genomic Imprinting

[Dan]

Annie,

If I understand it correctly, neither paternally imprinted nor
maternally imprinted alleles are expressed upon inheritance due to the
methylation of Cytosine in the DNA.

If that is the case, for the statement in the lecture notes
"Maternally imprinted genes are not transcribed because the embryos
have no Dad version". (are you saying that the main reason maternally
imprinted genes are not expressed is due to the fact that no Dad
version is present, or is it because of the methylated cytosine in DNA
in the regulatory region of the mom's allele) ?? Thanks... sorry to
ask so many questions :)

Dan

[Annie]

Hi Dan,
Sorry for the confusion!

> If I understand it correctly, neither paternally imprinted nor
> maternally imprinted alleles are expressed upon inheritance due to the
> methylation of Cytosine in the DNA.

In a given organism, maternally imprinted alleles are not expressed
from the mom's chromosomes, but ARE expressed from the dad's
chromosomes. Likewise, paternally imprinted alleles are not expressed
from the dad's chromosomes, but ARE expressed from the mom's
chromosomes.

Thus, the organism still expresses a given gene, but it expresses only
the paternal copy (in the case of maternally imprinted genes), or only
the maternal copy (in the case of paternally imprinted genes).

>
> If that is the case, for the statement in the lecture notes
> "Maternally imprinted genes are not transcribed because the embryos
> have no Dad version". (are you saying that the main reason maternally
> imprinted genes are not expressed is due to the fact that no Dad
> version is present, or is it because of the methylated cytosine in DNA
> in the regulatory region of the mom's allele) ?? Thanks... sorry to
> ask so many questions :)

The Maternally imprinted genes are not being transcribed because they
are methylated, and hence silenced. Normally, the organism would be
transcribing this allele from the chromosome it inherited from its
dad, but in this case, the organism never received a dad version.

Hope this helps!
-Annie