Short Cuts to Pedigree Chart
Analysis
Challenge Question: What process are we
seeing here?
• This is Mitosis
happening in onion
root cells
• Can you spot any of
the stages?
• Hint:
IPMAT
How to read a
pedigree chart
Step 1. figure out
which trait is
dominant, the
black or white
individuals?
There are 9 black and 7 white
• Let’s assume black is dominant
Step 2: Choose a letter (Like A) and assign
genotypes to each individual
• Its easiest to start
with the recessive
genotypes as these
are homogenous so
we know each white
individual must have a
genotype of ‘aa’
Step 3: Now you can work backwards from the
recessive genotypes to figure out the genotypes of
their parents using a punnet square
• For example:
• So if this offspring is
genotype ‘aa’ what
must the parents be?
They are dominant
(black) but are they
heterozygous or
homozygous?
Try writing the genotypes for the rest of the
pedigree chart for yourself…
Short cuts: Fill in the table on your worksheet
What does an autosomal
dominant pedigree look like?
In a pedigree this phenotype
will appear with equal
frequency in both sexes but it
will not skip generations. Here
is an example of an autosomal
dominant pedigree:
What does an autosomal recessive pedigree look
like?
Autosomal recessive pedigrees can look differently
based on the genotype of the parents. Here is an
example pedigree:
One trick for identifying a
recessive trait is that if a trait
skips a generation in a
pedigree, it is often an
autosomal recessive trait
These traits appear with
equal frequency in both
sexes.
X-linked recessive pedigree
• What does an X-linked recessive
pedigree look like?
• As you can see above, this trait is
more likely to appear in males than
females so the pedigree may
contain more affected males than
females
• This trait is never passed from
father to son, because a father
carries the allele on his X
chromosome, but always passes his
Y chromosome on to any sons.
• Here is a sample X-linked recessive
pedigree:
X-linked dominant
• How can you identify an X-linked dominant trait
• -This kind of trait affects both males and females equally and does
not skip generations
• -All affected males have an affected mother
• -All affected females have an affected father or mother
• -All female progeny of an affected male are affected