Genetics Problems



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Genetics Problems

There are actually very few human traits that show complete dominance or recessiveness. Most of our inherited traits involve some type of incomplete dominance or multigene inheritance. However, for introductory purposes, we will assume dominance as indicated in the following problems. The purpose of this exercise is to practice using the rules of inheritance to solve problems involving genotypes and phenotypes. Please do on a separate sheet of paper and show your work (either a punnett square or the probability math). Due 3/11/14




  1. Brown hair color (BB or Bb) is dominant over blond hair color (bb). What phenotypic ratio would you expect from the marriage of a brown haired male (Bb) and a blond haired female (bb)?

  2. Assume that brown eye color is dominant over blue eye color. What phenotypic ratio would you expect from a brown eyed male (Bb) and a brown eyed female (Bb)

  3. Farsightedness is dominant over normal vision. A normal sighted man (ff) marries a farsighted female (FF). What phenotypic ratio would you expect in their 8 children ?

  4. Long eyelashes are dominant over short eyelashes. A female with long eyelashes (Ll) marries a man with short eyelashes and together they produce 4 children. How many of these children would likely have long eyelashes like their mother?

  5. Small yellowish brown spots (freckles) on the face behave as dominants in heredity. What phenotypic ratio would you expect from a cross involving a freckle faced female (Ff) and a freckle faced male (Ff)?

  6. Actually, there are persons with freckles, and persons with “a whole lot of freckles” (scientific term). These 2 phenotypes seem to be associated with the genotypes FF and Ff. If the parents in #5 had a rather large family of 16 kids, what phenotypic ratio would you expect to find in their kids?

  7. Extra fingers on the side of the hand (polydactyl) are known to be dominant over normal finger number. A couple has 6 children, of which 3 were born with extra fingers. Give the likely genotypes for the parents and all 6 of the children. Although the parents appeared to have the normal finger number, it should be noted that most often, the extra finger is removed at the hospital before the baby leaves.

  8. Myopia (nearsightedness), is inherited as a recessive trait. Two nearsighted parents have 4 children. What percentage of the offspring would you expect to be of normal vision?

  9. Dimpled cheeks are dominant over non-dimpled individuals. What proportion of the offspring would you expect to have dimpled cheeks from a cross of 2 non-dimpled persons?

  10. Babies unable to fold their tongues in the shape of a “U” have trouble feeding after birth. Tongue folding is dominant over the inability to fold the tongue. See if you can fold your tongue into the shape of a “U”. Assume that a woman who can fold her tongue marries a man who cannot fold his tongue, and further that they have 20 children ALL of whom can fold their tongues. What are the likely genotypes of the kids?

  11. Give the phenotypic ratio of the offspring if a dark haired blue eyed female (Ddbb) marries a blond haired brown eyed male (ddBb).

  12. Freckles are dominant to clear skin and brown hair is dominant to blonde. A freckled face-brown haired female (FfHh) marries a freckled face-brown haired male (FfHh). What phenotypic ratio would they likely expect in their offspring?

  13. Curly hair and brown eyes are dominant to straight hair and blue eyes. The father had a genotype of CcBb and the mother had a genotype of Ccbb. What are the phenotypes of these two parents? What phenotypic ratio would they likely expect in their children?

  14. A brown eyed male with dark hair color (BbDd) marries a dark eyed female with blonde hair color (Bbdd). What % of their children would they expect to have brown eyes and blonde hair?

  15. Attached ear lobes and widow’s peak are dominant to free hanging ear lobes and no widow’s peak. What genotypic ratio would a couple expect to find in their offspring if their genotypes are both AaWw?

  16. A near sighted dimpled cheek female (nnDd) marries a normal sighted dimpled cheek male (NnDd). What % of their offspring would likely be near sighted and nondimpled?

  17. A freckled face far sighted male marries a clear skin-normal sighted female. What % of their offspring will likely have clear skin and be far sighted, unlike either parent? The parent’s genotypes are: dad (FfSs) and mom (ffss)

  18. Recently with the new trends in men’s hair-styles many men have been surprised to find that hair color and beard color are under the control of separate genes. In many cases, the hair color is not the same as beard color. The female’s genes, which are passed on to the sons, determine the hair color even though the genes have no effect in the female. A man with dark hair color on his head and a dark beard color marries a female with genes for dark hair color and blonde beard color. What phenotypic ratio would likely show up in their sons if their genotypes are: dad (BbDd) and mom (Bbdd)?

  19. Which sons in # 18 might be a surprise to the parents because they have hair combinations not seen in the father? (Assume they have 16 children and they follow the ratios perfectly described in #18)

  20. A gray bodied, normal winged fruit fly (GgNn) is crossed with a black bodied, vestigial winged female (ggnn). What phenotypic ratio will likely show up in their offspring?



  21. EXTRA CREDIT (partial credit if attempted): A female with attached ear lobes-freckles-dark hair (AaFfDd) marries a male with unattached ear lobes-clear skin-dark hair (aaffDd). What phenotypic ratio would you likely find in crosses of this type?



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