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Genetics Problems

set 1

1.  In squash the gene, W for white color, is dominant over its allele, w for yellow color.  What is the expected F1 phenotype from a cross between heterozygous white   and yellow ?

2.  In Rabbit brown fur (B) is dominant to white fur (b).   A brown furred Rabbit named Charley is crossed with a white furred Rabbit  and the progeny occur in the ratio of 50% brown to 50% white. What is the likely genotype of Charley ? 

3. The ability to roll one's tongue into a U-shape is determined by the presence
   of a non-sex linked dominant gene, T.  A man, unable to roll his tongue, and a woman able to roll hers, have four  children. The woman's mother couldn't roll her tongue, but her father could.    Of their four children how many might you expect to unable to roll their tongues ?

4. A couple has four children whose blood types are A, B, and AB.  Which of the parental genotypes is capable of producing the blood types  of this couples children ?
 5.  A human recessive genetic disease, termed Charlyitis, is found on chromosome 12   and is often fatal.  Suppose by chance that a boy, Michael, who has this disease    lives past puberty and marries a normal woman, but whose father also had Charlyitis.   If this couple have any children what is the probability that the children will have Charlyitis ?    

 6.  An allele for brown eyes B is dominant over that for blue eyes b. A couple of whom one is brown-eyed and the other blue-eyed have         eight    children, all brown eyed. What would be the genetic make up of each parent in this regard? For each parent state whether they are homozygous or heterozygous.

7.    A blue-eyed man, both of whose parents were brown-eyed, marries a woman. They have one child who is blue-eyed. What are the genotypes of all the individuals mentioned?

 8. A brown-eyed man whose father was brown-eyed and whose mother was blue-eyed married a blue-eyed woman whose father and mother were both brown-eyed. The couple has a blue-eyed son. For which of the individuals mentioned can you be sure of the genotype? What are the genotypes? What genotypes are possible for the others?  

9. A hybrid pink snapdragon was crossed with a pure white one. Red flower colour is incompletely dominant. Make a diagram to show:the gene constitution of the parents

genotypic and phenotypic ratios of the F2 generation]

 10.In the garden pea, Mendel found that yellow seed colour was dominant to green and round seed shape was dominant to shrunken. Determine the phenotypic and genotypic ratios for the F1 generation and the phenotypic ratio for the F2 if a plant with homozygous rounded yellow seeds is crossed with a plant with shrunken green seeds.

  11  Tall tomato plants are produced by the action of a dominant allele T and dwarf plants by its recessive allele t. Hairy stems are produced by a dominant gene H and hairless stems by its recessive allele h. A dihybrid tall, hairy plant is crossed with a dwarf hairless tomato plant. Determine the phenotypic ratio for the F1 generation.

 12  Black coat colour in Cocker Spaniels is dominant, while red coat colour is recessive; solid pattern is dominant, while spotted pattern is recessive. A solid black male is mated to a solid red female and produces a litter of six pups: two solid black, two solid red, one black and white, and one red and white. Determine the genotypes of the parents.

13.Chin fissure is controlled by a dominant allele and a smooth chin by a recessive allele. If the parents were heterozygous for the trait, the chance of producing a child with a chin fissure?

14. Albinism (lack of skin pigmentation) is caused by a recessive autosomal allele. A man and a woman, both normally pigmented, have an albino child. The mother is now pregnant again, and her doctor tells her she is carrying fraternal twins (resulting from two eggs between fertilized by separate sperm). What is the probability that both twins will have normal pigmentation?

15. In snapdragons plant color shows an incomplete dominance. Heterozygous plants have pink flowers, where as the two homozygotes have red flowers or white flowers. Two pink flowers are crossed. What proportion of their progeny would you predict would be pink?

16 If two heterozygous parents, CcDd, were crossed how many  possible combinations of GENOTYPES in the offspring

17. If tall is dominant to short, and purple flowers are dominant to white flowers, what is the phenotypic ratio of the potential offspring if you cross a short, white flower with a homozygous dominant tall, heterozygous purple flower?

18. Black fur in mice is dominant to brown fur (B – dominant allele, b-recessive allele). Short tails are dominant to long tails (T – dominant allele, t-recessive allele). What fraction of the progeny of the cross BbTt X BBtt would you predict would have black fur and long tails?

  19.  You are a genetic counselor and you have a couple that comes to you for advice.  The mother is heterozygous for normal and sickle cell hemoglobin (HbA/HbS) and heterozygous for types A and B glucose-6-phosphate dehydrogenase (G6PDA/G6PDB) and the father is heterozygous for sickle cell hemoglobin and hemoglobin C (HbC/HbS) and hemizygous for glucose-6-phosphate dehydrogenase type A- (G6PDA-).

a.  What genotypes and phenotypes do you predict for their offspring?

b.  What frequencies of the different combinations (both genotypes and phenotypes) are expected?

c.  What Mendelian principle or principles are illustrated by this problem?


a. What would the genotype frequencies and allele frequencies be in the next generation?

b. What is your long term prediction for allele frequencies if selection remains the same?




  1. A rooster with gray feathers is mated with a hen of the same phenotype. Among their offspring, 15 chicks are gray, 6 are black, and 8 are white. What is the simplest explanation for the inheritance of these colors in chickens? What offspring would you predict from the mating of a gray rooster and a black hen? 
  2. In some plants, a true-breeding, red-flowered strain gives all pink flowers when crossed with a white-flowered strain: RR (red) x rr (white) --- Rr (pink). If flower position (axial or terminal) is inherited as it is in peas (i.e., axial is dominant to terminal), what will be the ratios of genotypes and phenotypes of the generation resulting from the following cross: axial-red (true-breeding) x terminal-white? What will be the ratios in the F2 generation? 
  3. Flower position, stem length, and seed shape were three characters that Mendel studied. Each is controlled by an independently assorting gene and has dominant and recessive expression as follows:




Flower position

Axial (A)

Terminal (a)

Stem length

Tall (L)

Dwarf (l)

Seed shape

Round (R)

Wrinkled (r)


  1. If a plant that is heterozygous for any two characters were allowed to self-fertilize, what proportion of the offspring would be expected to be as follows? (Note: Use the rules of probability instead of a huge Punnett square.) 
    1. homozygous for the three dominant traits
    2. homozygous for the three recessive traits
    3. heterozygous
    4. homozygous for axial and tall, heterozygous for seed shape
  2. A black guinea pig crossed with an albino guinea pig produced 12 black offspring. When the albino was crossed with a second black one, 7 blacks and 5 albinos were obtained. What is the best explanation for this genetic situation? Write genotypes for the parents, gametes, and offspring. 
  3. In sesame plants, the one-pod condition (P) is dominant to the three-pod condition (p), and normal leaf (L) is dominant to wrinkled leaf (l). Pod type and leaf type are inherited independently. Determine the genotypes for the two parents for all possible matings producing the following offspring: 
      1. 318 one-pod normal, 98 one-pod wrinkled
      2. 323 three-pod normal, 106 three-pod wrinkled
      3. 401 one-pod normal
      4. 150 one-pod normal, 147 one-pod wrinkled, 51 three-pod normal, 48 three-pod wrinkled
      5. 223 one-pod normal, 72 one-pod wrinkled, 76 three-pod normal, 27 three-pod wrinkled
  4. Color patterns in a species of duck is determined by one gene with three alleles. Alleles H and I are semidominant (i.e., incomplete dominance), and allele i is recessive to both. How many phenotypes are possible in a flock of ducks that contains all the possible combinations of these three alleles. 
  5. Phenylketonuria (PKU) is an inherited disease caused by a recessive allele. If a woman and her husband are both carriers, what is the probability of each of the following? 
      1. all three of their children will be of normal phenotype
      2. one or more of the three children will have the disease
      3. all three children will have the disease
      4. at leastone child will be phenotypically normal
  6. The genotype of F1 individuals in a dihybrid cross is AaBb. Assuming independent assortment of these four genes, what are the probabilities that F2 offspring would have the following genotypes? 
      1. aabb
      2. AaBb
      3. AABB
      4. AaBB
      5. AaBB
  7. A stray black cat with unusual rounded, curled black ears was adopted by a family in California. Hundreds of descendants of the cat have since been born, and cat fanciers hope to develop the "curl" cat into a show breed. Suppose you owned the first curl cat and wanted to develop a true-breeding variety. How would you determine whether the curl allele is dominant or recessive? How would you select for true-breeding cats? How would you know they are true breeding? 
  8. What is the probability that each of the following pairs of parents will produce the indicated offspring (assume independent assortment of all gene pairs)? 
      1. AABB x aabb--- AaBb
      2. AABb x AaBb --- AAbb
      3. AaBb x AaBb --- AaBb
      4. aaBb x AABb--- AaBb
  9. In tigers, a recessive allele causes an absence of fur pigmentation (a "white tiger") and a cross-eyed condition. If two phenotypically normal tigers that are heterozygous at this locus were mated, what percentage of their offspring will be cross-eyed? What percentage will be white? 
  10. In corn plants, a dominant allele I inhibits kernel color, while the recessive allele i permits color when homozygous. At a different locus, the dominant gene P causes purple kernel color, while the homozygous recessive genotype pp causes red kernels. If plants heterozygous at both loci are crossed, what will be the phenotypic ratio of the F1 generation? 
  11. A man has six fingers on each hand and six toes on each foot. His wife and their daughter have the normal number of digits. Extra digits is a dominant trait. What fraction of this couple's children would be expected to have extra digits? 
  12. In mice, black color (B) is dominant to white (b). At a different locus, a dominant allele (A) produces a band of yellow just below the tip of each hair in mice with black fur. This gives a frosted appearance known as agouti. Expression of the recessive allele (a) results in a solid coat color. If mice that are heterozygous at both loci are crossed, what will be the expected phenotypic ratio of their offspring? 
  13. If the litter resulting from the mating of two short-tailed cats contains three kittens without tails, two with long tails, and six with short tails, what would be the simplest way of explaining the inheritance of tail length in these cats? Show genotypes (i.e., of all of the individuals mentioned). 
  14. In watermelons the genes for green color and for short shape are dominant over their alleles for striped color and for long shape. Suppose a plant with long striped fruit is crossed with a plant heterozygous for both these characters. What phenotypes would this cross produce and in what ratios? 
  15. In guinea pigs, black fur (B) is dominant over white fur (b). If one half of a particular litter were white, the genetic makeup of the parents was what?
  16. In sorghum plants, red stem is dominant over green stem. If 1,000 seeds from a sorghum plant germinated to produce 760 red plants and 240 green plants, it would be most reasonable to assume that the parental genotypes were what
      1. B is a dominant allele coding for black fur on rabbits and b is a recessive allele coding for white fur on rabbits. Fill in the following blanks with the correct cross of the
  17. A man and a woman each have dark eyes, dark hair, and freckles. The genes for these traits assort independently. The woman is heterozygous for each of these traits, but the man is homozygous. The dominance relationships of the alleles are as follows:
    1. What is the probability that their child will share the parents' phenotype?
    2. What is the probability that the child will share the same genotype as the mother?
    3. As the father?
  1. In cats with the Manx trait, the M (dominant) allele causes a short or absent tail, whereas the m allele confers a normal, long tail. Cats of genotype MM die as embryos. If two Manx cats mate, what is the probability that each living kitten has a long tail?
  2. Domesticated hens with white feathers and large, single combs mate with roosters that have dark feathers and small combs. The offspring all resemble their mothers for these two traits. (a) Which alleles are dominant, and which are recessive? (b) If the F1 generation are crossed with each other, what fraction of the F2 generation would be expected to have dark feathers and large, single combs?
  3. If the dominant allele K is necessary for hearing, and the dominant allele M of another independent loci (i.e., not linked) results in deafness no matter what other genes are present, what percentage of the offspring produced by the cross kkMm x Kkmm will be deaf?
  4. Work out the genotype of all carriers and affected individuals.



Soji Philip ,Head Teacher, Department of Biology,ICSK,Salmiya

©sojiiphilip 2008.


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