1. Unit 8: Mendelian Genetics
8.7 Pedigrees

2. What is a Pedigree?
Pedigrees study how a trait is passed from one generation to the next.
By recording phenotypes of family members
By observing the phenotypes of family members, we can infer the genotypes.
Remember, conditions and disorders can be carried on:
Autosomes (22 pairs of chromosomes)
Sex Chromosomes (X or Y)
Keep in mind: traits are influenced heavily by non- genetic factors or environmental factors
Examples: life style, geography, nutrition and exercise, toxins (mutagens), and disease and age.

4. Parts of a Pedigree Shapes: Lines: Filling: Identifying Individuals:
Squares are males (XY)
Circles are females (XX)
Diamond is undetermined sex
Lines:
Horizontal lines connect breeding couples
Vertical lines connect parents to children
A diagonal line means death.
Filling:
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
Identifying Individuals:
Roman Numerals show generations (oldest generation is on the top and youngest is on the bottom)
Numbers assign an individual to a generation and birth order (Oldest from left to right)

5. More Pedigree Symbols & Meanings

6. Interpreting Pedigrees
1. Determine if the trait is dominant or recessive.
Every other generation: it is recessive
Every generation: it is dominant

7. Interpreting Pedigrees
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”.

8. How to interpret a pedigree:
3. Assign genotypes to affected (shaded) individuals first.
If Autosomal then use two alleles to show inheritance.
Example: AA, Aa, aa
If Sex-linked then use one allele for males, two for females:
The shaded males will carry the gene (XcY) and be affected.
The females can be affected (XcXc) if they inherited two copies of the gene
4. Assign remaining genotypes to unaffected (unshaded) individuals.
If Sex-Linked: the unshaded males will not carry the gene (XCY) and not be affected), carriers marked with a dot or half shaded (XCXc), along with unshaded unaffected females (XCXC)
5. Double check your work, does the pedigree make sense?

9. Your Turn! Is this dominant or recessive?
Is this Autosomal or Sex-linked?
Assign genotypes to the pedigree to show the inheritance pattern.

10. Type of Inheritance? Autosomal dominant inheritance.
Check your work!
Type of Inheritance? Autosomal dominant inheritance.

11. Your turn! Is this dominant or recessive?
Is this Autosomal or Sex-linked?
Assign genotypes to the pedigree to show the inheritance pattern.

12. Type of Inheritance? Sex linked Recessive
Check your work.
Type of Inheritance? Sex linked Recessive