-Let’s take stock:
-Recall: We started off with Mendel and we were looking at his traits
and the simple model he came up with for the explanation of how these
traits were inherited from generation to generation. And of course, just
by looking around the room and observing the diversity of people that
we see, Mendel’s simple model obviously can’t explain all. We have a
lot of variation that exists out there that must be explained and
accommodated within this basic set of laws that Mendel established.
-A pt. that needs to be made today is that Mendel wasn’t wrong.
What Mendel observed was what he could observed and what he
observed actually, the basic laws hold true for everything that we’re
going to look at. But what he looked at was a fairly unelaborated story,
what we’re going to do now is elaborate Mendel’s simple laws so that
we can accommodate this variation.
-Now, amongst those people who started to bring together what was
known about cell biology with Mendel’s laws, establishing a little bit of
a wrinkle in that now we understand the cellular basis for the
inheritance mechanism that Mendel referred to are these 4 individuals
who established the chromosomal theory of inheritance: Nettie Stevens,
E.B. Wilson, T.H Morgan, and Calvin Blackman Bridges.
-Today we’ll build upon their findings & move beyond a simple
explanation for sex-linked traits that we looked at at the end of the last
lecture & we want to move on from here. We’ll move on from an
important observation that’s based on the pedigree & indeed, it’s based
on the observations that Thomas Hunt Morgan made w/ regards to what
one could view as being the co-segregation of sex determination, so
looking at sex determination of a trait, the co-segregation of that trait w/
some sort of visible trait such as haemophilia or eye colour in the case
of Morgan’s flies. It wasn’t just that the trait accompanied the sexuality
of the organism – its sex – but rather, if you view the determination of
the sex of the individual as being a trait, it means that 2 traits were
moving along together.
-So far, we’ve acted like genes function as individual entities in the
genome but they’re joined up on chromosomes & one might expect that
the genes would move together just like we’ve seen: sex determination
and something like eye colour in flies segregating together.