A student proposes that left-handedness is a recessive trait that is therefore hidden in much of the human population. A survey of a class of 36 students finds that 27 (0.75) are right-handed and 9 (0.25) are left-handed. Using the Hardy-Weinberg formula, what would the expected genotypes and allele frequencies be in this theoretical population?
A) 0.75 homozygous dominant and 0.25 homozygous recessive, and a 3-to-1, right-to-left handed allele ratio in the population.
B) 0.25 homozygous dominant, 0.50 heterozygous, and 0.25 homozygous recessive, and a 0.75 dominant allele frequency and a 0.25 recessive allele frequency.
C) 0.25 homozygous dominant, 0.50 heterozygous, and 0.25 homozygous recessive, and a 0.5 allele frequency for each allele.
D) 0.50 homozygous dominant, 0.25 heterozygous, and 0.25 homozygous recessive, and a 0.5 allele frequency for each allele.
E) They cannot be estimated using these limited data.

Question

Quizplus · Accepted Answer

To use the Hardy-Weinberg formula, we first need to calculate the allele frequencies:
-The total number of alleles in the population is 72 (each individual has 2 alleles).
-The number of dominant alleles (right-handedness) is 54 (27 students x 2 alleles per student).
-The number of recessive alleles (left-handedness) is 18 (9 students x 2 alleles per student).
-The frequency of the dominant allele is 54/72 = 0.75.
-The frequency of the recessive allele is 18/72 = 0.25.

Next, we can use the formula: p^2 + 2pq + q^2 = 1, where p is the frequency of the dominant allele and q is the frequency of the recessive allele.

Plugging in the values, we get:
-p^2 = frequency of homozygous dominant = (0.75)^2 = 0.5625
-2pq = frequency of heterozygotes = 2 x 0.75 x 0.25 = 0.375
-q^2 = frequency of homozygous recessive = (0.25)^2 = 0.0625

Therefore, the expected genotypes are: 
-0.5625 or 56.25% of individuals would be homozygous dominant (right-handed)
-0.375 or 37.5% of individuals would be heterozygous
-0.0625 or 6.25% of individuals would be homozygous recessive (left-handed)

The allele frequencies for both dominant and recessive alleles are 0.5.

A Student Proposes That Left-Handedness Is a Recessive Trait That