Activity

Try each of the following questions.

  1. PROBLEM #1.

    You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following:

    1. The frequency of the "aa" genotype.
    2. The frequency of the "a" allele.
    3. The frequency of the "A" allele.
    4. The frequencies of the genotypes "AA" and "Aa."
    5. The frequencies of the two possible phenotypes if "A" is completely dominant over "a."
       
  2. PROBLEM #2.

    Sickle-cell anemia is an interesting genetic disease. Normal homozygous individuals (SS) have normal blood cells that are easily infected with the malarial parasite. Thus, many of these individuals become very ill from the parasite and many die. Individuals homozygous for the sickle-cell trait (ss) have red blood cells that readily collapse when deoxygenated. Although malaria cannot grow in these red blood cells, individuals often die because of the genetic defect. However, individuals with the heterozygous condition (Ss) have some sickling of red blood cells, but generally not enough to cause mortality. In addition, malaria cannot survive well within these "partially defective" red blood cells. Thus, heterozygote's tend to survive better than either of the homozygous conditions. If 9% of an African population is born with a severe form of sickle-cell anemia (ss), what percentage of the population will be more resistant to malaria because they are heterozygous (Ss) for the sickle-cell gene?
     

  3. PROBLEM #3.

    There are 100 students in a class. Ninety-six did well in the course whereas four blew it totally and received a grade of F. Sorry. In the highly unlikely event that these traits are genetic rather than environmental, if these traits involve dominant and recessive alleles, and if the four (4%) represent the frequency of the homozygous recessive condition, please calculate the following:

    1. The frequency of the recessive allele.
    2. The frequency of the dominant allele.
    3. The frequency of heterozygous individuals.
       
  4. PROBLEM #4.

    Within a population of butterflies, the color brown (B) is dominant over the color white (b). And, 40% of all butterflies are white. Given this simple information, which is something that is very likely to be on an exam, calculate the following:

    1. The percentage of butterflies in the population that are heterozygous.
    2. The frequency of homozygous dominant individuals.
       
  5. PROBLEM #5.

    A rather large population of Biology instructors have 396 red-sided individuals and 557 tan-sided individuals. Assume that red is totally recessive. Please calculate the following:

    1. The allele frequencies of each allele.
    2. The expected genotype frequencies.
    3. The number of heterozygous individuals that you would predict to be in this population.
    4. The expected phenotype frequencies.
    5. Conditions happen to be really good this year for breeding and next year there are 1,245 young "potential" Biology instructors. Assuming that all of the Hardy-Weinberg conditions are met, how many of these would you expect to be red-sided and how many tan-sided?
       
  6. PROBLEM #6.

    A very large population of randomly-mating laboratory mice contains 35% white mice. White coloring is caused by the double recessive genotype, "aa". Calculate allelic and genotypic frequencies for this population.
     

  7. PROBLEM #7.

    After graduation, you and 19 of your closest friends (lets say 10 males and 10 females) charter a plane to go on a round-the-world tour. Unfortunately, you all crash land (safely) on a deserted island. No one finds you and you start a new population totally isolated from the rest of the world. Two of your friends carry (i.e. are heterozygous for) the recessive cystic fibrosis allele (c). Assuming that the frequency of this allele does not change as the population grows, what will be the incidence of cystic fibrosis on your island?
     

  8. PROBLEM #8.

    You sample 1,000 individuals from a large population for the MN blood group, which can easily be measured since co-dominance is involved (i.e., you can detect the heterozygotes). They are typed accordingly:

    BLOOD TYPE
    GENOTYPE
    NUMBER OF INDIVIDUALS
    RESULTING FREQUENCY
    M
    MM
    490
    0.49
    MN
    MN
    420
    0.42
    N
    NN
    90
    0.09

    Using the data provide above, calculate the following:

    1. The frequency of each allele in the population.
    2. Supposing the matings are random, the frequencies of the matings.
    3. The probability of each genotype resulting from each potential cross.
       
  9. PROBLEM #9.

    Cystic fibrosis is a recessive condition that affects about 1 in 2,500 babies in the Caucasian population of the United States. Please calculate the following.

    1. The frequency of the recessive allele in the population.
    2. The frequency of the dominant allele in the population.
    3. The percentage of heterozygous individuals (carriers) in the population.
       
  10. PROBLEM #10.

    In a given population, only the "A" and "B" alleles are present in the ABO system; there are no individuals with type "O" blood or with O alleles in this particular population. If 200 people have type A blood, 75 have type AB blood, and 25 have type B blood, what are the allelic frequencies of this population (i.e., what are p and q)?

Click here to find the answers to the above questions.

Go Further

Try the demo problems 1 - 4 found on this site. Click on each link to obtain the problem.

Have a look at this site and a simulation about eye colour.
Click on the link entitled "What colour will your children's eyes have?". Perform the simulation. On the right hand slide is a slider that allows you to change the allelic frequencies for each trait of eye colour. Perform the simulation under various conditions by changing the slider.