Transcript Human Pedigrees

Human Pedigrees
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Pedigrees are a convention for keeping
track of human genetic traits used to infer
genotype.
Pedigrees are the human equivalent of test
crosses.
In a visualization of a pedigree:
males are designated with square symbols.
females with round symbols
lines are drawn to indicated matings,
parent-offspring relationships, and
relationships between siblings.
Drawing Pedigrees
► requires
an old fashioned pencil and paper
Symbols
► Before
we consider human inheritance we
need to learn the symbols used to draw
pedigrees. The figure below shows some of
the commoner symbols:
Note that the symbols for non-identical twins and
for identical twins differ by whether they descend
from a common vertical before bifurcating
Pedigrees
► Generations
are numberered from the top of
the pedigree in uppercase Roman numerals,
I, II, III etc. Individuals in each generation
are numbered from the left in arab
numberals as subscripts, III1 , III2, III3 etc.
For example, here is a typical autosomal
dominant pedigree with numbered
generations and individuals.
Sample Pedigree
Try It!
► Let
us begin by drawing the pedigree
described below (which is not necessarily an
autosomal dominant condition and which
contains extraneous information).
The Scenario
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Alice and Bob have a two year old son, Charles, who is
showing mental retardation, short stature, micropenis, and
cryptorchidism. Alice has two living, unaffected, brothers
but her eldest brother died at age 9 and a second brother
died aged 10 months. Both had similar problems to
Charles. Alice's father, David, who was symptomless, has a
sister, Ethel, who has an unaffected boy and girl, and a
brother, Fred, who also has two unaffected children. Alice's
mother, Gertrude, has two living sisters and had a brother
who had died in childhood and who, she remembers, had
been mentally retarded. Bob has two brothers, Henry and
Ignatius, who are still unmarried. His parents, John and
Kate, had tragic lives, both were adopted and never knew
their biological parents and both died as the result of a
road accident.
Step 1
► Begin
with Alice, Bob
and Charles.
► Here are three possible
drawings of this
nuclear family.
Correct Solution
► Alice
and Bob are connected by a horizontal
line to show that this is a mating. Charles is
connected to that horizontal line to show
that he is a product of that mating.
Step 2
► Now
add Alice's siblings and parents to the
pedigree.
Choose One…
Correct Solution was Possiblilty 3
Alice and her four brothers are
connected vertically to a
horizontal line which is, in turn,
connected to the line drawn
between her parents David and
Gertrude. Her two dead brothers
(whom we presume died of the
same genetic disease - though
this can sometimes be a foolish
assumption without medical
evidence) are shaded in (to show
that they suffered from the
disease) and are crossed through
(to show that they are dead).
Step 3
► Now
add Gertrude's siblings to the pedigree.
► And David's siblings and his nephews and
nieces
► Finally add Bob's side of the family
► Try Drawing it!!!
Correct Drawing!