Question

"Draw a pedigree for hitchhiker’s thumb. Your pedigree should cover at least two generations and include both dominant and recessive forms of the trait. Label the pedigree with genotypes, using the letter H to represent the dominant allele for the trait and the letter h to represent the recessive allele."
I'm confused on the part about having two generations. How do I set up the pedigree?

Answer 1

Answer and Explanation:

First, you need to know how to interpret a pedigree representation.

• Family members

→ Individuals are represented with geometrical figures.

→ Males are squares

→ Females are circles

• Trait/Phenotype

→ Healthy/normal/not affected  individuals are represented with empty figures

→ Affected/mutated individuals are represented with solid black figures

• Generations

→ Each file is represented with a roman number, indicating the Generation.

 

Now, what we need to do is to draw a pedigree for a hitchhiker’s thumb. We know that this is an autosomal dominant trait, which we will represent with an H. No hitchhiker's thumb is the recessive trait, and it will be represented with an h.

Our pedigree should cover at least two generations and include both dominant and recessive forms of the trait.    

1. We can cross two heterozygous individuals, Hh, who are the first generation in our pedigree.
2. This cross will result in a woman and a man with No hitchhiker's thumb, another man with a hitchhiker's thumb, HH, and another woman with a hitchhiker's thumb, Hh. These individuals will represent the second generation in the pedigree.
3. Finally, we can cross the man with No hitchhiker's thumb, hh, with a woman who does not have a hitchhiker's thumb either, hh. And the woman with a hitchhiker's thumb, Hh, with a man with a hitchhiker's thumb, HH. The result of these crosses will be the third generation.

The representation would be like following,

I → First-generation: First cross

• Man Hh (1)  
• Woman Hh (2)

II → Second-Generation: F1 and second crosses

• Man hh (3)  x    Woman hh (4)
• Woman hh (5)
• Man HH (6)
• Woman Hh  (7) x   Man HH (8)

III → Third-Generation:

• A boy (9) and a girl (10) hh
• A girl (11) HH

You will find this pedigree in the attached files. In this example, we included three generations. The first one belongs to the grandparents, the second one to parents, aunts/uncles, and the third one to grandchildren.  

If you draw another pedigree, remember to include

• the figures representing males and females,
• color and H/h representing the phenotype,
• Roman numbers representing the generations, and optional, numbers naming each member.