To determine which organism is most closely related to the common ancestor, we need to compare the DNA sequences provided and calculate the differences, known as Hamming distances, between the common ancestor and each of the modern species. The organism with the smallest Hamming distance to the common ancestor is the most closely related.
The DNA sequences for the comparison are as follows:
- Common Ancestor: AATGGGCCTAATCCA
- Bear: AATGGCTCTAATCCA
- Dog: AATGGGCGTAATCCA
- Mouse: ATCGGCCCTAATGCT
- Rat: ATCGGCCCTATTGCT
We'll calculate the Hamming distances for each pair:
1. Common Ancestor and Bear:
- Compare: AATGGGCCTAATCCA (ancestor) with AATGGCTCTAATCCA (bear)
- Differences:
- 6th position: G (ancestor) vs T (bear)
- 8th position: C (ancestor) vs T (bear)
- Hamming distance = 2
2. Common Ancestor and Dog:
- Compare: AATGGGCCTAATCCA (ancestor) with AATGGGCGTAATCCA (dog)
- Differences:
- 7th position: C (ancestor) vs G (dog)
- Hamming distance = 1
3. Common Ancestor and Mouse:
- Compare: AATGGGCCTAATCCA (ancestor) with ATCGGCCCTAATGCT (mouse)
- Differences:
- 2nd position: A (ancestor) vs T (mouse)
- 3rd position: T (ancestor) vs C (mouse)
- 4th position: G (ancestor) vs G (mouse) - similar
- 5th position: G (ancestor) vs C (mouse)
- 6th position: G (ancestor) vs C (mouse)
- 14th position: C (ancestor) vs G (mouse)
- Hamming distance = 5
4. Common Ancestor and Rat:
- Compare: AATGGGCCTAATCCA (ancestor) with ATCGGCCCTATTGCT (rat)
- Differences:
- 2nd position: A (ancestor) vs T (rat)
- 3rd position: T (ancestor) vs C (rat)
- 4th position: G (ancestor) vs G (rat) - similar
- 5th position: G (ancestor) vs C (rat)
- 9th position: A (ancestor) vs T (rat)
- 14th position: C (ancestor) vs G (rat)
- Hamming distance = 6
Comparing the Hamming distances:
- Bear: 2
- Dog: 1
- Mouse: 5
- Rat: 6
The smallest Hamming distance is 1, which corresponds to the Dog. Therefore, the organism most closely related to the common ancestor is:
A. Dog
