This is a hypothetical example. The pedigree for a mongenic trait is given below. The shaded individuals show spotted skin color while the rest have uniform skin color. The individuals (1 to 9) in the pedigree were analyzed for a DNA marker (both fragments) that shows complete linkage with the skin color trait.

The following statements were made regarding the above observations:
A. Spotted skin color is a dominant phenotype.
B. Spotted skin color shows variable expressivity.
C. The DNA marker associated with the skin color trait is co-dominant.
D. The probability that the individual 5 will pass on the allele responsible for the spotted skin color to the next generation is 0.25.
Which one the following options represents the combination of all correct statements?

Correct option is B

Explanation:

The pedigree shows the inheritance of a spotted skin color trait, and the DNA markers for the individuals in the pedigree have been analyzed. Here are the evaluations of each statement:

• A. Spotted skin color is a dominant phenotype:

  • The shaded individuals (1, 5, 7) exhibit the spotted skin color, indicating that the trait is likely dominant because it appears in heterozygous individuals (like the union of parents 1 and 2, where one parent is homozygous for the uniform skin color and the other carries the spotted trait).

• B. Spotted skin color shows variable expressivity:

  • This is not directly indicated in the pedigree. There is no clear pattern to suggest varying expressivity (e.g., different intensity or manifestation of the trait) in the individuals who carry the trait.

• C. The DNA marker associated with the skin color trait is co-dominant:

  • The co-dominance of the DNA marker is suggested by the pedigree analysis, as both alleles (represented by different fragments in the individuals' DNA) show clear inheritance patterns linked to the skin color trait. The marker shows both bands (in the individuals) associated with spotted skin color.

• D. The probability that the individual 5 will pass on the allele responsible for the spotted skin color to the next generation is 0.25:

  • This statement is incorrect. Based on the pedigree and considering individual 5 (heterozygous for the spotted trait), the probability of passing the dominant allele to offspring is 50%, not 25%. This suggests a dominant inheritance pattern, not a recessive one.

Information Booster:

1. The dominance of spotted skin color in the pedigree suggests the trait is governed by a dominant allele.

2. The DNA marker analysis shows linkage with the skin color trait, confirming co-dominance.

3. Co-dominance occurs when both alleles contribute equally to the phenotype, which is observed in the DNA banding pattern.

4. The expression of a dominant trait like spotted skin color could be uniform across individuals, without significant variability in expressivity.

5. Dominant traits typically appear in individuals with at least one dominant allele, while recessive traits require two copies of the recessive allele.

6. The probability of genetic inheritance follows Mendelian laws. Individual 5, being heterozygous, has a 50% chance of passing on the dominant allele.

Additional Information:

• A and B: While A is correct about the dominant nature of the trait, B assumes variable expressivity, which is not indicated in the pedigree data.

• A and C: Both A and C are correct, with C confirming co-dominance of the DNA marker associated with the trait.

• B and C: B lacks support from the data, making B and C an invalid pair.

• C and D: While C is correct, D is inaccurate based on the pedigree analysis.