Introduction to Cell & Molecular Biology (BIOL121) - Dr. S.G. Saupe (; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321

Three Dozen Genetics Problems for Your Intellectual Entertainment

  1. What is the genotype of all possible gametes (assume the genes are autosomal, aren't linked, and that there is no crossing over) from an  individual with each of the following:
    a.  MM         b.  Zz    c.  AaBB    d. RrTt  e.  AAbbCcDDEEff

  2. For each of the above, how many genes (and chromosomes) are represented? Can you sketch the chromosomes?

  3. For each of the above, indicate whether the individual would exhibit the dominant or recessive phenotype.

  4. In garden peas, the allele for yellow seeds (G) is dominant to the allele for green seeds (g).  What offspring and in what proportions would be expected from the following crosses?
         heterozygous x heterozygous
    heterozygous x homozygous yellow
         homozygous yellow x homozygous green

  5. Black coat color in guinea pigs is the result of a dominant allele (W), and white coat color the result of a recessive allele (w).  A black female guinea pig produces a white offspring. What is her genotype? What genotypes and phenotypes could the male have had? What phenotypes and in what ratio would her offspring be from a test cross?

  6. Albinism in humans, the lack of pigmentation, is a recessive trait.  A man and a woman plan to marry and wish to know the probability of their having any albino children.  What would you tell them in the following situations?
    both are normally pigmented but each has an albino parent the man is albino
         the woman is normal but her father is an albino
    the man is albino and the woman's family includes no albino's for at least three generations.

  7. If two individuals with normal skin pigmentation have an albino child, what is the genotype of each parent?  What is the probability that the next child will be a albino?

  8. A streak of white in an otherwise uniformly colored head of hair is known as a white forelock.  It is dominant to the normal allele.  If a woman with a white forelock marries a normal male and their first child is  normal, what is her genotype?

  9. A pea plant with yellow seeds (dominant) is crossed with a plant with green  (recessive) seeds.  The resulting offspring produce about equal numbers  of green and yellow seeds. Give the genotypes of both parents.

  10. My wife has a widow's peak.  Linda's mother does not have a widow's peak, nor do I.  What is the probability that Erin and Amy have a widow's peak?

  11. In humans, brown eyes are usually dominant over blue eyes.  If a blue-eyed  man marries a brown-eyed woman whose father was blue-eyed, what proportion of their children would you predict will have blue eyes?

  12. If a brown-eyed man marries a blue-eyed woman and they have ten children,  all brown-eyed, can you be certain that the man is homozygous?  If the eleventh child has brown eyes will that prove what the father's genotype is?


  1.  _____ Linda and I can both roll our tongues (dominant)  Therefore, Amy and Erin must both be able to roll their tongues.

  2. _____ I can roll my tongue.  Thus, my genotype must be rr.

  3. _____ If a couple has a child that cannot roll her tongue, then both of the parent's must also not be able to roll their tongues

  4. _____ I cannot taste PTC paper (recessive), but Linda can.  Thus, there is a 75% chance that Erin can taste PTC paper.

  5. _____ Amy must have at least one recessive allele for PTC paper

  6. _____ Woody Guthrie, Arlo's Dad, died of Huntington's disease (dominant).  Therefore, one of his parent's had this disease.

  7.  _____ Assuming that Woody's wife did not have Huntington's disease, there is a 50% chance that their son, folksinger Arlo, has Huntington's disease.

  8. _____ Linda has blood type A.  I have type O blood.  Therefore, Erin and Amy must both have type A blood.

  9. _____ If Linda and I have another child, there is no chance that the child will have type O blood.

  10. _____ Freckling is due to a dominant allele.  If the "Beav" has freckles, but Wally (his brother) doesn't, then Ward and June (their parents) must both be heterozygous.

  11. _____ Linda has a hitchhiker's thumb (recessive).  Thus, Amy and Erin must each have at least one allele for hitchhiker's thumb.

  12. _____ George is colorblind (X-linked recessive), but his wife Evelyn has normal eyesight.  Thus, their son Ralph must be colorblind.   

  13. _____ There is a 50% chance that Evelyn's and George's daughter is colorblind.

  14. _____ If a couple both have type AB blood, there is no chance that their children will have type O blood.

  15. _____ Familial hypercholesterolemia (FH) is due to a single, dominant gene.  This trait, which is the most common, Mendelian disorder, results in elevated levels of cholesterol in blood, early onset of arteriosclerosis and a 25 times greater risk of heart attack than a normal individual.  The chance that two normal individuals will have a child with FH is zero.

  16. _____ Widow's peak is a dominant trait.  Linda, Erin and Amy all have a widow's.  I do not.  Erin and Amy must be heterozygous for widow's peak.

  17. _____ If you have attached ear lobes (recessive trait), then one of your parent's must also have attached ear lobes.

  18. _____ If a man and a woman both have blood type B, none of their children can have blood type O.

  19. _____ Eye color is determined by the action of several genes

  20. _____ In peas, smooth (S) seeds are dominant to rough (s).  If a cross between two plants yields 918 smooth and 305 rough seeded individuals, then the parent plants must have had the genotypes Ss x ss.

  21. _____ In humans, wet ear wax is dominant to dry.  If a man with dry was marries a woman with wet wax and whose father had dry wax, then 25% of their children would be expected to to have dry wax.

  22. _____ Albinism in humans is a recessive trait.  If two individuals with normal pigmentation have an albino child then the parents were both heterozygous

  23. _____ It is impossible for two albino parents to have a normally pigmented child.

  24. _____ Freckling is due to a dominant allele.  If Wally and Beaver have freckles, then both Ward and June must, too.

  25. _____ The odds of picking an ace from a deck of cards is 1/52 

  26. _____ The probability of tossing a coin and it landing heads is 1/2

  27. _____ The probability of tossing a coin twice and it landing heads both times is 1/2

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Last updated: July 14, 2009     � Copyright by SG Saupe