- In a population of 2000 individuals of a plant species, genetic difference at a single locus leads to different flower colours. The alleles are incompletely dominant. The population has 100 individuals with the genotype rr (white flowers), 800 individuals with the genotype Rr (pink flower) and the remaining have genotype RR (red flowers). What is the frequency of the r allele in the population?
(1) 0.25 (2) 0.50
(3) 0.75 (4) 1.00How to Calculate the Frequency of the r Allele in a Plant Population with Incomplete Dominance
Allele frequency calculations are fundamental in population genetics, especially when dealing with traits showing incomplete dominance. In such cases, each genotype can be directly observed through its phenotype, making calculations straightforward and accurate.
Problem Overview
-
Total population: 2000 individuals
-
Genotype counts:
-
rr (white flowers): 100
-
Rr (pink flowers): 800
-
RR (red flowers): 2000 – 100 – 800 = 1100
-
Step 1: Understand the Genotype Contributions
Each plant has two alleles:
-
rr: 2 r alleles per individual
-
Rr: 1 r allele per individual
-
RR: 0 r alleles per individual
Step 2: Calculate the Total Number of r Alleles
-
rr: 100 × 2 = 200
-
Rr: 800 × 1 = 800
-
RR: 1100 × 0 = 0
Total r alleles = 200 + 800 = 1000
Step 3: Calculate the Total Number of Alleles
-
Each individual has 2 alleles.
-
Total alleles = 2000 × 2 = 4000
Step 4: Calculate the Frequency of the r Allele
Frequency of r=Number of r allelesTotal alleles=10004000=0.25
Step 5: Match with the Provided Options
-
(1) 0.25
-
(2) 0.50
-
(3) 0.75
-
(4) 1.00
The correct answer is (1) 0.25.
Why This Calculation Is Important
-
Population genetics: Accurate allele frequency estimates are crucial for tracking genetic variation and predicting future changes in populations.
-
Plant breeding: Knowing allele frequencies helps breeders select for desired traits.
-
Conservation: Understanding genetic diversity helps preserve endangered plant species.
Conclusion
In a population of 2000 plants with incomplete dominance at the flower color locus, the frequency of the r allele is 0.25. This demonstrates the power of Hardy-Weinberg principles and simple allele counting in real-world genetics.
-
