Download Human Pedigrees - PSimpsonBiology

4.3.12 Human Pedigrees
Drawing and Analysis
Genetic Counseling
• Helping individuals and prospective
parents
• Your learning gives you the opportunity
to determine some probabilities and
patterns of inheritance yourself!
Determining Risk
Probability of inheriting a particular gene
is dependent on parents’ genes.
Sometimes information about a parent is
not enough or unknown.
We use genetic information about other
family members to help “solve the
puzzle” as best as possible
Pedigrees
A pedigree is a biological family tree that
shows the interrelationships between
parents and children across generations.
Helps illustrate a pattern of inheritance
for a single trait through that family
Pedigrees
Standard Symbols in Pedigrees
Male
Female
Unspecified
Gender
Standard Symbols in Pedigrees
Clinically
Unaffected
Clinically
Affected
Carrier
Not
Clinically
Affected
Standard Symbols in Pedigrees
SB #wk
Deceased
Still Birth /
miscarriage
Conventions in Drawing Pedigrees
Parents
Regardless of Social
Relationship
Male partner on left
(usually)
Conventions in Drawing Pedigrees
I
1
2
II
1
2
Full Siblings
3
(in order of age from left to right)
Conventions in Drawing Pedigrees
I
1
2
II
1
2
3
4
Dizygotic Twins Monozygotic Twins
Conventions in Drawing Pedigrees
I
Separated
1
2
3
Blood Relative
II
Adopted
1
2
3
Patterns of Inheritance
• Dominant:
– Trait is expressed in every generation
• eg. Huntington’s, brown eyes
– Not seen in offspring unless present in a
parent
• Recessive:
– Trait may skip generations
• eg. TaySachs
• Sex-Linked:
– Y linked – only males are clinically affected
– X linked – affected males may have normal
parents, affected females must have
affected father
Simple Pedigrees
• Pg. 138 DBQ
• Pg 140 DBQ
• Pg 145 DBQ
Determining Risk
Several individuals in Ms. Soule’s family
have been diagnosed with either Breast
Cancer (BRCA) or Polycystic kidney
(PKD).
PKD vs. healthy kidney
Ms. Soule would like to know
what risk she has of
developing these
conditions.
b) Ms Soule’s Pedigree – Matrilineal/Genetic
(1) I have a daughter. I have one sister and she has a son and a daughter.
My mother has a sister and a brother. My mother’s sister has two daughters.
My mother’s brother has a son and a daughter. My maternal grandmother was
second youngest of sisters. (2) The oldest of my maternal grandmother’s
sisters had four daughters. The eldest of these had two daughters of her own
and she also developed breast cancer. (3) The next of my grandmother’s
sisters had one daughter. Her daughter and husband both died from
polycystic kidney disease. (4) The youngest of my grandmother’s sisters had
two sons. One of those sons had one daughter; the other had one son and a
daughter. (5) My grandmother’s mother had a sister. My grandmother’s
maternal grandmother died of breast cancer. My maternal grandmother’s
mother had breast cancer and so did my grandmother. Two of my
grandmother’s sisters had breast cancer (not the one whose family showed
polycystic kidney disease).
1) Which disease should Ms Soule be more worried about PKD or breast CA?
2) Breast CA has not been seen in Ms Soule’s family in her generation or her
parent’s generation. Does that mean she is not at risk? What kind of
inheritance is this?
Pedigree Problems
a) Ms Soule’s Pedigree – Social
I am married to Peter. I have one sister, Lindsay. She is married to Joe and has
a (cute!) son, Jeremy. My parents (Doug and Judy) are both alive and still
married. My dad is an only child, but my mom has a brother, Pete, and a sister,
Becky. 1) Becky was married to Jeff and had two daughters (Amy and
Addy) and one miscarriage. 2) They divorced and both remarried. 3) Jeff’s
new wife had a son from a previous marriage and together they had a
second son. Becky and her new husband did not have any kids. My uncle Pete
married Chris and had a son, Mark, and a daughter, Stephanie. Stephanie is
married with two daughters and a son of her own. Pete and Chris divorced, and
Pete remarried Barbara, who has one son from a previous marriage. Her son is
married and has a son and daughter. My mom’s parents are still alive and
married. 4) My dad’s parents divorced, and his mom remarried Joseph who
had two children from a previous marriage, but I don’t know if they’re boys
or girls. 5) My father’s father passed away.