Suppose a population is carrying a condition controlled by two alleles: r (dominant) and r (recessive). only homozygous individuals that have two copies of the recessive allele have the condition. if the r allele is found in 15 percent of the population, what's the frequency of the rr genotype?

a. 2.25 percent
b. 25.5 percent
c. 72.25 percent
d. 12.75 percent

The answer is C. 72.25 percent.

The Hardy-Weinberg principle can be used:

p² + 2pq + q² = 1 and p + q = 1

where p and q are the frequencies of the alleles, and p², q² and 2pq are the frequencies of the genotypes.

The r allele (q) is found in 15% of the population:
q = 15% = 15/100
Thus, q = 0.15

To calculate the R allele frequency (p), the formula p + q = 1 is used:
If p + q = 1, then p = 1 - q
p = 1 - 0.15
Thus, p = 0.85

Knowing the frequency of the R allele (p), it is easy to determine the frequency of the RR genotype (p²):
p² = 0.85² = 0.7225

Expressed in percentage, p² = 72.25%.

interphase

the period of cell growth when the cell synthesizes new molecules and organelles. the cell is not dividing and it constitutes the majority of the time spent in the cell cycle

prophase

changes occur in the nucleus and cytoplasm. the chromatin condenses to form structures (sister chromatids) visible with a light microscope and the mitotic spindle begins to form, but the nucleus is still in tact

prometaphase

the nuclear envelope fragments and the spindle microtubules attach to the kinetochores of the sister chromatids

metaphase

all the cell's duplicated chromosomes are lined up at an imaginary plane equidistant between the poles of the mitotic spindle

anaphase

begins when sister chromatids separate from each other and ending when a complete set of daughter chromosomes arrives at each of the two poles of the cell

telophase

the daughter nuclei form at the two poles of a cell

cytokinesis

the division of a cytoplasm to form two separate daughter cells. usually occurs during telophase during mitosis. this and mitosis make up to mitotic (m) phase of the cell cycle