- What he means by the anatomy of a pedigree is what does it look like, what
are the features of that particular pedigree and let’s take a look at some of the
features that we should think to encounter in a pedigree and we’ll see male,
female individuals that are going to be involved in mating and giving rise to
progeny. This is in the slide so males are squares and females are round, etc.
- Progeny is shown in order of birth, the earliest born to the most recent born
going left to right.
- Going over to the other side then is the number of children of a given sex
which can be indicated in abbreviated forms of pedigrees.
- We have affected individuals (displaying trait) displayed with a filled either
square or circle and heterozygous individuals for autosomal recessive traits are
shown by the half filled square or circle.
- Every now and then within a pedigree we’ll find dizygotic (fraternal twins)
and every now and again we’ll find monozygotic twins shown in a similar
manner but a link between the two of them to show NOT THAT THEY
MATED but that they’re identical twins.
- So for sex unspecified again b/c historically it wasn’t known. For example
that the individual was predeceased & one didn’t know what sex the individual
was & speaking of which of course death is going to be a feature of some of
these as well so death is a square or a circle with a line through it & every now
& then you will have either a chosen or spontaneous abortion or stillbirth &
generally sex is unspecified in this particular instance.
- This individual is sometimes also called the pro-band, that is the propositous
or the person proposing to have the pedigree done, the person who is wanting
to find out about their genetic heritage generally.
- Then finally, we have a method of identifying persons within a pedigree so
instead of referring to them by name, give them numbers and we have the
propositous with the arrow as individual number 2 in this particular pedigree.
- Normally for the examples we’ll be provided with, this is exactly how the
pedigree would be shown with these #s to talk about generation I, individual 1,
generation II, individual 3 for example is what they will ask us about.
- Here is a special case here, this is inbreeding so for those of us that know our
Latin languages, con sanguineous is with blood so it is mating with a blood
relative & that is shown by a double line & he will come back to that in a
couple of slides.
- Here is an important one we won’t deal with today and that is carrier of a sex-
linked recessive trait so these are traits that are carried not on autosomal
chromosomes but on sex chromosomes.
- Sometimes the pedigrees look slightly different and he is just giving us a
heads up on this regard, we are pretty well tied in to using pedigrees available
from literature and sometimes they look slightly different so he wanted to just
give us a heads up. Sometimes we’ll see these designators for some of the
things that he has talked about in the previous slide, he won’t go over them
- Adoption indicated by a dotted line so nonrelated individuals. Identical twins
indicated by a slightly different mechanism in this example here.
- In this instance it is called the proband but it is the same as the propositous.