Question

The pedigree below shows the inheritance of free earlobes and attached earlobes in 5 generations of a family. Attached earlobes are caused by a recessive allele (f). How many children of individuals 1 and 2 have free earlobes?

A. 0
B. 1
C. 2
D. 3
E. 4

Answer 1

General Formulas and Concepts

Genetics II

Pedigrees

• Generations
• Symbols

Application

Step 1: Define

Let's label the pedigree so that we can understand it better.

The first generation would start at the top, with the last generation at the bottom.

• Individuals 1 and 2 are the first generation
• Individuals 3, 4, and 5 are the second generation
• Individuals 6, 7, 8, and 9 are the third generation
• Individuals 10, 11, 12, and 13 are the fourth generation
• Individual 14 is the fifth generation

As the key mentions, colored-in squares and circles signify whether a male or female, respectively, has attached earlobes or not.

• Individuals 1, 4, 10, 11, 12, and 13 all have attached earlobes
• Individuals 2, 3, 5, 6, 7, 8, and 9 all have free earlobes

Step 2: Work

Let's now find the answer to our question.

1. [Pedigree] Look for the first generation:
   The first generation is found at the top of the pedigree.
2. [Pedigree] Identify the number of children of individuals 1 and 2:
   The number of children produced by individuals 1 and 2 is 2, individuals 3 and 4.
3. [Pedigree] Identify how many of those children have an attached earlobe:
   Between individuals 3 and 4, we can see only individual 4 has an attached earlobe and only individual 3 has a free earlobe.

Answer

∴ the answer to our question is B. 1.

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Topic: Biology

Unit: Genetics II