Pedigree – Understanding heritable traits
Imagine you are a geneticist who is interested in tracing the occurrence of a genetic disorder through several
generations of a family. One important tool geneticist use to trace inheritable traits in humans is a pedigree. A
pedigree is a chart of “family tree” that tracks which members of the family have a particular trait. The trait in a
pedigree can be an ordinary trait such as widow’s peak, or a genetic disorder such as cystic fibrosis. You can use
various traits in your family if you’d like- artistic ability, musical ability, grumpiness, etc. Be creative!
A pedigree – diagram- is a type of way of looking at how genes and appearances (pheonotypes) are passed from one
generation to the next. Pedigrees and knowledge that each parent contributes one version of a gene to a child,
pedigrees can be used to predict which genes parents and/or children have. In addition, it can also be used to
predict the appearance of an unborn child.
Lesson Time: Home. Ms. Thennis will check a rough draft prior to the final draft if you’d like.
Materials- poster board, ruler, colored pencils, paper, and video of how to create a pedigree
(https://www.youtube.com/watch?v=Wuk0W10EveU)
Lesson: This lesson uses observations of heritable traits and the knowledge that each parent contributes genetic
information to create a diagram representing a family tree. An example tree (pedigree) is then used to predict the
specific genotype to go with the phenotypes.
Procedure
Organize thoughts and explain inheritance patterns from pedigree Procedure
1) Choose a trait to research in your family from the list below or approved by your teacher.
2) Gather information from interviewing family members- try to include your parents, siblings, grandparents,
aunts, uncles, cousins. If a child is adopted don’t include them in the pedigree
3) Create a pedigree chart using the symbols below. Your pedigree should include the following: relationship to
you, denotation of male or female, proper shading to indicate inheritance, possible genotypes, and phenotypes.
4) Must have three generations and include cousins, uncles, etc if possible.
5) A half-page summary of the type of inheritance the pedigree shows- complete dominance, autosomal
recessive trait, autosomal dominant, sex-linked, incomplete dominance or complete dominance.
Use your books and online to create a pedigree. You should not put Punnett squares on your pedigree but you need to figure out the
genotypes when you can. Sometimes you may have more than one beside your circle or square. Make a key and follow the
requirements below for the assignment.
Grade for Pedigree Creation
Points
Requirements
5
Use of poster board – size between 16” X 12” or 32” X 32”
3
Title and clearly marked generations with roman numeral I, II, III
3
Lines drawn with ruler
5
At least 12 individuals/ and three generations shown
4
Clear key
5
Genotypes included (some may be possible genotypes) of all individuals
10
Overall Appearance – neatness and proper use of pedigree symbols.
Colorful (2)
Creativity (2)
Neatness (2) Type and glue information if you don’t have nice handwriting
Use a compass, template and ruler for squares and circles (4)
0
Actual pictures or drawings of family members – Extra Credit- 5 pts.
35
Total
Traits
Complete Dominance – all autosomal traits
Trait
Eye Color
Vision
Hair
Facial Features
Appendages
Others
Dominant Trait
Brown
Farsighted
Normal vision
Dark Hair
Widow’s peak
Mid- digit hair on fingers
Dimples
Unattached earlobes
Freckles
Broad lips
Cleft in chin
Long eyelashes
Extra digits
Short digits
Double- jointed
Tongue rolling
Hitchhikers thumb
Incomplete Dominance
Curliness
Curly – homozygous
dominant
PTC/Bitter
Homozygous dominant –
Tasting
strong taster
Skin Color
Homozygous dominant –
dark skin color
Tay – Sachs
Homozygous dominantDisease
no disease
Sickle Cell
Dominant- no disease
Disease
Recessive Trait
Grey, green, blue, hazel
Normal vision
Near Sighted
Light, red, curly
Normal hairline
No hair
No dimples
Attached earlobes
No freckles
Thin lips
No cleft
Short eyelashes
Normal number
Normal digits
Normal joints
Inability to roll tongue
Non hitchhiker thumb
Wavy- heterozygous
Straight – homozygous recessive
Heterozygous – weak taster
Homozygous recessive – non-taster
Heterozygous- “medium” color
Homozgyous recessive –light skin
color
Homozygous recessive – disease
Heterozygous- half the necessary antibodies- half
without
Heterozygous – half the number of normal hemoglobin
Homozygous recessive- abnormal
and ½ abnormal hemoglobin (sickle cell) *heterozygous
cells- sickle cells
combinations offers protection against malaria
Codominant Traits (expression of both- red + white + red and white)
Trait
Blood Type
AB Blood type- allele for A and B are both expressed
Sex-linked traits
Trait
Dominant Trait
Recessive Trait
Baldness
No- disease – males or females
Disease- in males/carriers in females (males
X Y)
Hemophilia
No disease males (X Y) or females (X X)
Disease in males (X Y) carriers in females (X
X)
Duchennes Muscular Dystrophy
No disease in males (X Y) or females. (X X)
Disease in males (X Y) carriers in females (X
X)
Colorblindness
No colorblindness in males (X Y) or females.
Colorblindness in males (X Y) carriers females
(X X)
(X X)
Multiple Allles
Blood Type
A and B are both dominant
O (ii) is recessive
Alleles possible include the A, B or O- can only inherit 2.
*Know that many of the traits above may be considered polygenic traits, but for the purpose of the pedigree you can consider them complete,
incomplete, codominance, sex-linked or multiple alleles. Height, skin color, eye color are polygenic traits because they are influenced by more
than one allele at different locations on the chromosomes (loci).
You can also use a trait not listed above and determine the inheritance based on the pattern shown in the family. Ideas include – creativity,
helpfulness, introvert, and extrovert, etc.
3. Bent little finger (dominant)
Use this family to determine which versions of the gene each person has, when possible.
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KEY:
Other relationships that students may ask about: