Directions: Use the information provided and your knowledge of Life Science to answer the following questions. Show all work where necessary.
Directions: Use the information provided and your knowledge of Life Science to answer the following questions. Show all work where necessary.
Labrador retrievers are a classic example used to study how DNA and chromosomes code for characteristic traits. Most people recognize three common coat colors in Labs: black, chocolate (brown), and yellow. These visible differences arise from specific DNA sequences in genes that influence pigment production. By examining these genes and their locations on chromosomes, scientists can connect molecular information in DNA to the traits passed from parents to offspring.
Two key genes contribute to Labrador coat color: MC1R (often called the “E” locus) and TYRP1 (often called the “B” locus). The MC1R gene helps control whether dark pigment (eumelanin) is produced in the fur. When the dominant allele E is present, eumelanin can be deposited, allowing black or brown coats to appear. However, dogs that inherit two copies of the recessive allele e (genotype
Diagram 1.
Source: https://www.snowypineswhitelabs.com/guides/does-a-labs-coat-color-matter/
The TYRP1 gene influences whether the eumelanin pigment appears as black or brown. Dogs with at least one dominant B allele can produce black pigment. Dogs that inherit two recessive b alleles (genotype
The combination of alleles at both loci determines the dog’s coat color. For example, a dog with genotype
Diagram 2.
Source:
https://dogchart.com/labrador-retriever-color-chart.html
This system demonstrates how DNA sequences – organized into genes on chromosomes – encode information for specific traits. It also shows how interactions between genes (epistasis) change the resulting phenotype. By asking questions about which alleles are present, how they interact, and how they are inherited, students can clarify the relationships between DNA, chromosomes, and observable characteristics in offspring.
Table 1.
MC1R Genotype (E/e) | TYRP1 Genotype (B/b) | Predicted Coat Color |
|---|---|---|
EE | BB | Black |
Ee | Bb | Black |
ee | BB | Yellow |
EE | bb | Chocolate |
Ee | bb | Chocolate |
ee | Bb | Yellow |
Graph of Information - Figure 1.
Table 2.
Litter ID | Number Black Pups | Number Chocolate Pups | Number Yellow Pups |
|---|---|---|---|
L1 | 4 | 2 | 1 |
L2 | 3 | 1 | 2 |
L3 | 5 | 1 | 2 |
L4 | 2 | 3 | 1 |
L5 | 4 | 2 | 1 |
Graph of Information - Figure 2.
According to Table 1, which genotype combination produces a chocolate Labrador?
Using the reading and Diagram 1, explain how the MC1R gene influences whether dark pigment (eumelanin) is deposited in Labrador fur.
Using Table 2 and Figure 1, describe one mathematical trend in the observed coat-color totals across the five litters.
Using Table 2 and Figure 2, explain how the observed proportions of each coat color compare to predicted proportions based on the parental genotypes.
Based on Table 1 and the reading, why do EeBb parents produce all three coat colors in a single litter?
Explain how the MC1R and TYRP1 genes – located on chromosomes – work together to produce the three main Labrador coat colors. Organize your response as Claim, Evidence, and Reasoning.