1. Pedigree Worksheet Key

2. Steps you should use to determine if a pattern of inheritance is possible for a particular pedigree…
Assign your alleles for a particular pattern of inheritance
Write the genotypes that would correspond to each individual on the pedigree for the chosen pattern of inheritance
If all the genotypes “work,” this pattern of inheritance is possible for the pedigree

3. Patterns of Inheritance: Alleles, Genotypes, and Phenotypes
Pattern of Inheritance
Alleles
Possible Genotypes and Associated Phenotypes
Autosomal Dominant
A = trait
a = normal
AA = trait
Aa = trait
aa = normal
Autosomal Recessive
A = normal
a = trait
AA = normal
Aa = normal
aa = trait
Sex-linked Dominant
XA = trait
Xa = normal
XA XA = female, trait
XA Xa = female, trait
Xa Xa = female, normal
XAY = male, trait
XaY = male, normal
Sex-linked Recessive
XA = normal
Xa = trait
XA XA = female, normal
XA Xa = female, normal
Xa Xa = female, trait
XAY = male, normal
XaY = male, trait

4. Pedigree #1

5. Trying Out Pattern Of Inheritance A: Autosomal Recessive
This pattern of inheritance does work! Aa Aa aa
AA or Aa
AA or Aa
AA or Aa

6. Trying Out Pattern Of Inheritance B: Autosomal Dominantaa aa
Impossible: This pattern of inheritance doesn’t work!
Aa or AA

7. Trying Out Pattern Of Inheritance C: Sex-Linked Recessive (aka X-Linked Recessive)
This pattern of inheritance does work! (if the mother is a carrier)
XAY
XAXa
XaY
XAY
XAXA or XAXa
XAXA or XAXa

8. Trying Out Pattern of Inheritance D: Sex-Linked Dominant (aka X-Linked Dominant)
Impossible: This pattern of inheritance doesn’t work!
XaY
XaXa
XAY

9. Trying Out Pattern of Inheritance E: Y-Linked
Impossible: This pattern of inheritance doesn’t work! If a son displays the trait, the father must display the trait as well because Y-linked traits are passed from father to son.

10. Final Answer
The two possible patterns of inheritance for the Pedigree #1 are autosomal recessive and x-linked recessive. We would have to see more of the pedigree to know which one is correct!

11. Pedigree #2

12. Trying Out Pattern Of Inheritance A: Autosomal Recessive
Impossible: This pattern of inheritance doesn’t work! aa aa Aa

13. Trying Out Pattern Of Inheritance B: Autosomal Dominant
This pattern of inheritance does work! Aa Aa aa aa
Aa or AA
Aa or AA

14. Trying Out Pattern Of Inheritance C: Sex-Linked Recessive (aka X-Linked Recessive)
Impossible: This pattern of inheritance doesn’t work!
XaY
XaXa
XAY

15. Trying Out Pattern of Inheritance D: Sex-Linked Dominant (aka X-Linked Dominant)
XAY
XAXa
This pattern of inheritance does work! (if the mother is a carrier)
XaY
XaY
XAXA or XAXa
XAXA or XAXa

16. Trying Out Pattern of Inheritance E: Y-Linked
Impossible: This pattern of inheritance doesn’t work! If a father displays the trait, the sons must display the trait as well because Y-linked traits are passed from father to son.

17. Final Answer
The two possible patterns of inheritance for the Pedigree #2 are autosomal dominant and x-linked dominant. We would have to see more of the pedigree to know which one is correct!

18. Pedigree #3

19. Trying Out Pattern Of Inheritance A: Autosomal Recessive
This pattern of inheritance does work! aa
AA or Aa
AA or Aa aa

20. Trying Out Pattern Of Inheritance B: Autosomal Dominant
Impossible: This pattern of inheritance doesn’t work! aa aa
Aa or AA

21. Trying Out Pattern Of Inheritance C: Sex-Linked Recessive (aka X-Linked Recessive)
Impossible: This pattern of inheritance doesn’t work!
XAY
XAXa
XaXa

22. Trying Out Pattern of Inheritance D: Sex-Linked Dominant (aka X-Linked Dominant)
Impossible: This pattern of inheritance doesn’t work!
XaY
XaXa
XAY

23. Trying Out Pattern of Inheritance E: Y-Linked
Impossible: This pattern of inheritance doesn’t work! If a son displays the trait, the father must display the trait as well because Y-linked traits are passed from father to son.

24. Final Answer
The one possible pattern of inheritance for Pedigree #3 is autosomal recessive.

25. Pedigree #4

26. Trying Out Pattern Of Inheritance A: Autosomal Recessive
This pattern of inheritance does work! Aa Aa aa aa

27. Trying Out Pattern Of Inheritance B: Autosomal Dominant
This pattern of inheritance does work! Aa aa aa aa Aa Aa

28. Trying Out Pattern Of Inheritance C: Sex-Linked Recessive (aka X-Linked Recessive)
This pattern of inheritance does work!
XaY
XAXa
XaXa
XAY
XAY
XaXa

29. Trying Out Pattern of Inheritance D: Sex-Linked Dominant (aka X-Linked Dominant)
XAY
XaXa
This pattern of inheritance does work!
XaY
XaY
XAXa
XAXa

30. Trying Out Pattern of Inheritance E: Y-Linked
Impossible: This pattern of inheritance doesn’t work! If a father displays the trait, the sons must display the trait as well because Y-linked traits are passed from father to son.

31. Final Answer
The four possible patterns of inheritance for Pedigree #4 are autosomal recessive, autosomal dominant, X-linked recessive, and X-linked dominant. We would have to see more of the pedigree to know which one is correct!