1. Pedigrees & Genetic Disorders
6C Pedigrees, Family Traits
Tracking Genetic Disorders through Generations

2. Pedigrees
Simple way to model inheritance of characters over generations
Often used to track genetic disorders in families
Any disease or disorder that is inherited

3. Pedigrees
In tracking the inheritance of recessive genetic disorders, individuals can carry the genetic information for a genetic disorder but not show the trait
They are called carriers
How can a parent carry the genetics for a recessive disorder without showing the trait?

4. Pedigrees To use a pedigree, you must understand the symbols:
Square = male
Circle = female
Shaded = trait

5. Pedigrees
If the trait is recessive, what are the genotypes of these individuals?

6. Pedigrees
If the trait is dominant, what are the genotypes of these individuals?

7. More Pedigree Symbols

8. Where is the P generation? I
Where is F1 gen? II
Where is F2 gen? III
IN EACH GENERATION, YOU LABEL INDIVIDUALS BY BIRTH ORDER – II-3, III-5
What is the name of ___ individual?
What color are the ind that show the trait?

9. Determining If The Trait Is Dominant or Recessive
First question to ask…..
Expressed in every generation?
Dominant
Skip generations?
Recessive

10. Dominant Trait Additional Checks
If you think it is DOMINANT, double check:
1) Every affected individual has at least one affected parent
2) Affected individuals who mate with unaffected individuals have a 50% chance of transmitting the trait to each child
3) Two affected individuals may have unaffected children.
RECESSIVE

11. Recessive Trait Additional Checks
If you think it is RECESSIVE, double check:
1) An individual who is affected may have two parents who are not affected
2) All the children of two affected individuals are affected

12. Where is the P generation?
Where is F1 gen?
Where is F2 gen?
IN EACH GENERATION, YOU LABEL INDIVIDUALS BY BIRTH ORDER – II-3, III-5
What is the name of ___ individual?
What color are the ind that show the trait?
Is this dominant or recessive? DOMINANT

13. RECESSIVE

14. DOMINANT

15. RECESSIVE

16. RECESSIVE

17. Autosomal dominant

19. Auto Dom 19

20. Auto Dom 20

21. Autosomal Recessive 21

22. Auto Dom 22

23. Auto Rec 23

24. Autosomal Recessive 24

25. Auto Dom 25

26. Human Chromosomes In humans, we have 46 chromosomes
23 homologous pairs
Homologous pairs are the same shape and size and code for the same traits

27. Human Chromosomes
Locate the 23rd pair
X and Y
XX = female
XY = male

28. Human Chromosomes 22 pairs of AUTOSOMES 1 pair SEX-LINKED chromosomes
(otherwise known as Somatic)
Non sex-linked
1 pair SEX-LINKED chromosomes
Used to determine gender

29. Gender Chromosomes
The X and Y chromosomes not only determine our gender but they also code for other traits as well
Some genetic information can be affected by our gender chromosomes
Presence of XX or XY

30. Gender Chromosomes
If a genetic disorder is linked specifically to the X or Y chromosome then depending if you are male (XY) or female (XX), you may have a higher or lower probability of inheriting the disorder

31. Examples of X-linked Traits
Color Blindness
2. Hemophilia: lacking the ability to clot blood
3. Muscular Dystrophy: weakening or loss of muscles

32. Analyzing X-Linked and Y-Linked Traits
Are only males affected?
Y-Linked
If the alleles for a trait are on the Y chromosome, then only males can have it
Only males have a Y chromosome

33. Y Linked 33

34. Y-Linked Traits If a male shows the trait for a y-linked disorder…
All of his sons will also show the trait
All of his sons must inherit the Y from dad, so if dad’s Y carries a disorder, all subsequent males will also have the disorder

35. Y Linked 35

36. Y-Linked Only males are affected?
Is the trait expressed in males and females?
Sex-Linked

37. X-Linked Inheritance
Sex-Linked traits are expressed unequally in males and females
In sex-linked traits, if any females are affected it must be x-linked
X-linked dominant and x-linked recessive

38. X-Linked Disorders X-Linked disorders are more difficult
Unaffected male X (Y)
Affected male X+ (Y)
Unaffected female XX
Affected if dominant XX+
Not affected if recessive
Affected female X+X+

39. X-Linked Inheritance
Pedigrees of x-linked traits show special patterns that differentiate it from autosomal disorders
On x-linked pedigrees, I will tell you that it is x-linked, otherwise assume autosomal or y-linked

40. X-Linked Dominant Affected male  all females affected
Affected male  no sons
Homozygous female  all children
Heterozygous female  some children

41. All daughters from affected male are affected

42. X Dominant
Add II-3 Homozygous mother
Without heterozygous mother 42

43. X-Linked Recessive Affected female  all sons affected
Carrier female  not all sons affected

44. X Rec 44

45. X Recessive 45

46. Affected male  All sons affected