Not all traits are going to be located on
chromosomes that are in the nucleus. This
is where we are going to look at exceptions
to the chromosomal theory of inheritance because
these things are not going to exhibit Mendelian
style inheritance patterns. The example here,
first of all, is looking at mitochondria.
We know that mitochondria contain their own DNA
and when we have a sperm fertilized in egg
clearly, the sperm doesn't have room for much
cytoplasm and so the egg is the contributor
of all the cytoplasm and thus all of the mitochondria
and thus all of the mitochondrial DNA. We
have identified that there are a number of
genes on the mitochondrial chromosomes that
end up being expressed and we can trace this
maternal inheritance through multiple generations
to identify relationships between individuals.
Mitochondrial DNA has to follow female lineage.
And the other place that we will see exceptions
to chromosomal theory is in the blossoming
field of epigenetics. Epigenetic factors are
any factors that influence gene expression
that are epi, above the genome. We have the
DNA sequence. We have all the genes on our
nuclear DNA, but as you learn later on, there
are many regions of our genome that are not
expressed as genes. They don't code for proteins.
However, we now know that these regions we
used to call junk DNA have a lot of impact
on the expression of genes and in the environment
has a large impact on these epigenetic factors.First
of all, we will look at a couple of different
mechanisms in which DNA packing is impacting
whether genes can be expressed and as well
as that DNA methylation, which affects somewhat
how the genes pack, but also we can see that
there are dietary impacts. The kind of stuff
we are consuming can actually impact how genes
are expressed, which is kind of revolutionary.
This is new stuff and then we can also see
that the environment impacts if we were in
expose to lots of teratogens or very high
levels of stress, the environment can certainly
cause changes to the epigenome and affect
gene expression and later on in this series,
you will learn a little about transposable
elements. Jumping genes, they can go from
one place to other in the genome and impact
gene expressions. These are all epigenetic
factors. Also multiple parts of the genome
are involved in regulating gene expression.
One example, we will see here is small RNA
sequences that interact with DNA as it packs.