Transcript Pedigrees

Pedigrees
• Pedigrees study how a trait is passed
from one generation to the next.
• Infers genotypes of family members
• Disorders can be carried on…
– Autosomes (22 pairs of chromosomes)
– Sex Chromosomes (X or Y)
– Number of Chromosomes
(either X>46>X)
• Keep in mind: traits are influenced
heavily by non-genetic factors or
environmental factors
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Nutrition
Exercise
Toxins (mutagens)
Disease
Parts of a
Pedigree
• Squares are males (XY)
• Circles are females (XX)
• Horizontal lines connect breeding
couples
• Vertical lines connect parents to
children
• Shading means the individual has the
trait
• Half shading or a dot means they
carry the gene called a “carrier”
• No shading means the individual does
not have the trait
• A diagonal line means death.
• Roman numerals show generations
• Numbers assign an individual to a
generation
– Example: What happened to II, 4?
Interpreting Pedigrees
• 1. Determine if the
trait is dominant or
recessive.
– Every other
generation: It is
recessive
– Every generation:
It is Dominant
• 2. Determine if the trait is
autosomal or sex linked.
– Affects males and females
equally: Autosomal (Aa)
– Affects one sex more than the
other: especially MALES!
Sex-linked (XCXc or XcY)
• Typically sex-linked disorders or
traits are carried on the X
chromosome
– Females tend to “carry” a trait and
affect their sons.
– Females get the trait from an
affected father or carrier/affected
mother
– Affected males got it from their
mother and give it to their
daughters to “carry.”
Interpreting
Pedigrees
Recap on interpreting pedigrees
1. Determine if it is dominant or recessive.
2. Determine if it is autosomal or Sex-linked.
3. Assign genotypes to affected (shaded) individuals first.
– If Autosomal then use two alleles to show inheritance.
(AA, Aa or aa for example)
– In Sex-linked the shaded males will carry the gene (XcY) and be
affected.
– In Sex-linked the females can be unaffected, affected or carriers
and marked with a dot. (XCXc)
4. Assign remaining genotypes to unaffected individuals .
– In Sex-linked the unshaded males will not carry the gene (XCY) and be
unaffected.
5. Double check your work, does the pedigree make sense?
Your Turn!
Is this dominant or recessive? Autosomal or Sex-linked?
Assign genotypes to the pedigree to show the inheritance pattern.
Check your work
Autosomal dominant inheritance.
Sex-Related Punnet Squares
•
The genes for these traits are on the X chromosome,
because boys only receive one X chromosome they are
more likely to inherit disorders passed to them from
their mother who would be a carrier.
– Humans have 22 pairs of autosomes and 1 pair of
sex chromosomes
– Males are XY
• Males donate their Y chromosome to their sons only
and their X chromosome to their daughters.
• They determine the sex of the child!
– Females are XX
• Females donate either one of their X chromosomes to
their sons and daughters
• Many times in women the other X chromosome coils
up and deactivates to become a Barr body.
•
Hemophilia and Colorblindness are sex linked traits, the
punnett square shows how a woman who is a carrier
passes the trait to her son, but not her daughters.
– In what only case could you have a daughter with
hemophilia and/or colorblindness?
– She inherits a recessive from her mother and her father!
Your Turn!
• A mother whose
father had
hemophilia marries a
man without
hemophilia.
• What is the
probability they have
children with the
disorder?
– Use H for normal and
h for hemophilia
Check your work
• First you should figure out
the genotypes of the
parents. If the mother had
a father with hemophilia,
then she is a carrier XHXh
and the father is normal
since he does not have
hemophilia himself. XHY
• They have a 50% chance of
having a boy with
hemophilia; 0% chance for
a daughter with
hemophilia.
Your turn!
Is this dominant or recessive? Autosomal or Sex-linked?
Assign genotypes to the pedigree to show the inheritance pattern.
Check your work.
Sex linked Recessive