Transcript Making a Pedigree Chart

Understanding a
Pedigree
Chart
A family history of a genetic
condition
Quick Review
• Genotype = what genes someone has
• Genes are usually represented by a letter, a
capital letter for the dominant trait, a small case
for the recessive.
• Example: Tongue Rolling is dominant, so we use R
to represent the tongue rolling
• Inablility to roll your tongue is recessive so we
use r to represent the non-rolling gene
• For every trait, you get a gene from each parent
Genotypes and Phenotypes
• Mom and Dad are Rr-that
is their genotype, they can
also be described as
heterozygous- they have 1
of each gene
• What is their
PHENOTYPE?
• The youngest son has a
genotype of rr-he is
Homozygous recessive-2
copies of the recessive
gene
• His phenotype?
I can’t
Roll my
Tongue!
Some common dominant and
recessive traits
• Widow’s peak is
dominant.
• You can be
homozygous dominant
(WW) or
heterozygous (Ww)
and you will have
widow’s peak
• What is your genotype
and phenotype if
you’re homozygous
recessive?
Making a Pedigree Chart
• Pedigree charts are
made to chart family
history and see how
traits are passed
• A genetic counsellor
will use pedigree
charts to help
determine the
distribution of a
disease in an
affected family
Symbols
• Shade individuals
that have the trait
you’re studying
• Boys = squares
(Lucy always calls
Charlie Brown a
‘block head’)
• Girls = circles
Making a Pedigree Chart
• Married-connected at
side
• Siblings-connected at
TOP not at the side
(hopefully not siblings
AND married)
• Oldest child-to the
left
• Question-if shaded
individuals in this
pedigree have blue
eyes, what is the
GENOTYPE of the
parents?
Other
• Divorced,
separated
• Deceased
• Identical twins
• Fraternal twins
Organizing the pedigree
chart
Generations are identified by Roman
numerals
I
II
III
IV
Organizing the pedigree
chart
• Individuals in each generation are identified
by Arabic numerals numbered from the left
• Therefore the affected individuals are II3,
IV2 and IV3
I
1
II
III
IV
2
3
4
5
6
7
What’s going on?
Shaded = blue eyes
• 1 and 2 split after
having 4, 2 then had
kids with 3 and split
with her too after 5-9
were born
• Genotypes of 1, 4,7?
• Genotypes of 2 & 3?
• Genotypes of 5,6, 8, 9,
10, 11, 12?
Make your own pedigree
• Using your own family, make your own
pedigree chart
• Must at LEAST include grandparents,
parents, & your generation
• Pick one easy dominant or recessive trait
and shade individuals that have it. You
can guess who has it if you don’t know for
sure. (Don’t pick a trait that EVERYONE
in your family has)
• Label yourself, grandparents, cousins, etc
• Put a key on the pedigree so I know
what shaded means. Ex.- shaded people
have widow’s peak
OR…you may create a pedigree chart for a
fictional family of your choice. For
example, a family in a book you read or a
movie you have seen (ex: Twilight series,
Harry Potter, etc)