Problem Analysis:
The image provided is a
pedigree chart, which is commonly used in genetics to represent the inheritance of traits within a family. The goal is to analyze the pattern of inheritance for a particular trait, which is indicated by the filled circles and squares (black symbols) representing affected individuals, while unfilled symbols represent unaffected individuals.
#### Key Observations:
1.
Symbols:
- Filled circles/squares (black): Affected individuals.
- Unfilled circles/squares: Unaffected individuals.
- Circles represent females, and squares represent males.
2.
Generations:
- Generation I: Parents.
- Generation II: Offspring of Generation I.
- Generation III: Offspring of Generation II.
3.
Trait Pattern:
- The trait appears to be inherited in a specific manner, and we need to determine whether it follows an
autosomal dominant,
autosomal recessive,
X-linked dominant, or
X-linked recessive pattern.
#### Step-by-Step Solution:
##### Step 1: Identify Affected Individuals
-
Generation I: Individual 2 is affected (filled circle).
-
Generation II: Individuals 3, 4, and 5 are affected (filled squares and circles).
-
Generation III: Individuals 3, 4, and 5 are affected (filled circles).
##### Step 2: Analyze the Inheritance Pattern
1.
Autosomal Dominant:
- In an autosomal dominant trait, if one parent is affected, there is a 50% chance that each offspring will inherit the trait.
- Here, individual 2 (Generation I) is affected, and her offspring (individuals 3, 4, and 5 in Generation II) are also affected. This suggests a dominant pattern.
2.
Autosomal Recessive:
- In an autosomal recessive trait, both parents must be carriers (heterozygous) for the offspring to be affected (homozygous recessive).
- However, individual 1 in Generation I is unaffected, and yet their offspring (individuals 3, 4, and 5 in Generation II) are affected. This does not fit the recessive pattern.
3.
X-Linked Dominant:
- In an X-linked dominant trait, the trait is expressed in both males and females, and affected males will pass the trait to all their daughters.
- Individual 3 in Generation II is male and affected, and his daughters (Generation III) are also affected. This fits the X-linked dominant pattern.
4.
X-Linked Recessive:
- In an X-linked recessive trait, the trait is typically expressed in males and passed from carrier females to their sons.
- However, individual 3 in Generation II is male and affected, and his daughters (Generation III) are also affected. This does not fit the recessive pattern.
##### Step 3: Conclusion
The pattern of inheritance in this pedigree chart is consistent with
X-linked dominant inheritance. Here’s why:
- The trait is expressed in both males and females.
- Affected males (e.g., individual 3 in Generation II) pass the trait to all their daughters.
- The presence of the trait in multiple generations, even when one parent is unaffected, supports the dominant nature of the trait.
Final Answer:
$$
\boxed{\text{X-linked dominant}}
$$
Parent Tip: Review the logic above to help your child master the concept of pedigree genetics worksheet.
