Suppose the human trait for earlobe type is controlled by a simple dominant and recessive relationship at one locus. free earlobes, e, is the dominant allele, and attached earlobes, e, is the recessive allele. in a college genetics class, the professor takes a tally of students who have free earlobes and of students with attached earlobes. in this class of 117 students, 37 have free earlobes. calculate the frequency of the dominant allele, e, and the heterozygous genotype, ee. express the frequencies in decimal form rounded to the nearest thousandth. assume the class is in hardy–weinberg equilibrium for this trait.

The frequency of the E allele is 0.173

The frequency of the Ee genotype is 0.286

Explanation:

Free earlobes (E) is dominant over attached earlobes (e).

The class is in Hardy–Weinberg equilibrium for this trait, so the genotypic frequencies are:

Where p is the frequency of the E allele and q is the frequency of the e allele.

In a class of 117 students, 37 have free earlobes (EE + Ee genotypes) and thus 80 students have attached earlobes (ee).

The frequency of the ee genotype (q²) is then 80/117, so we can calculate q:

q² = 80/117

q= √0.684

q= 0.827

The frequency of the e allele is 0.827

p + q = 1, so p = 1-q = 0.173

The frequency of the E allele is 0.173

The frequency of the heterozygous genotype Ee is:

freq Ee = 2pq = 2 × 0.827 × 0.173 =

freq Ee =  0.286

an individual’s sex (i.e., whether they are a male or female) is determined by the sex chromosomes. most people have two sex chromosomes, one that is inherited from their mother and one that is inherited from their father. typically, females have two x chromosomes (xx) and males have one x chromosome and one y chromosome (xy). conditions caused by changes (“mutations”) in genes located on the x chromosome are considered x-linked.

x-linked recessive inheritance

most x-linked conditions are recessive. this means that in a person with two x chromosomes (most females), both copies of a gene (i.e., one on each x chromosome) must have a change or mutation whereas in a person with one x chromosome (most males), only one copy of a gene must have a mutation. a female with a mutation in one copy of a gene on the x chromosome is said to be a “carrier” for an x-linked condition. a male with a mutation in a gene on the x chromosome is typically affected with the condition. because females have two copies of the x chromosome and males have only one x chromosome, x-linked recessive diseases are more common among males than females. however, x-linked recessive diseases can occur in both males and females.

for x-linked recessive disorders, an unaffected carrier mother who has a mutation in a gene on the x chromosome can transmit either the x chromosome with this mutation or a “normal” x chromosome to her children. if the father is unaffected, none of her daughters will be affected and all of her daughters will be unaffected—since they will inherit at least one normal x chromosome from their father. however, each daughter will have a 50% chance of being an unaffected carrier like her mother and a 50% chance of both x chromosomes being normal.

you know they are heterozygous for a trait because they have it as jj or jj.