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Punnett Square Practice Problems

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					Punnett Square Practice Problems 1. Cross a homozygous dominant tall pea plant with a heterozygous pea plant. T= tall and t = short a. What percentage will be short? b. What percentage will be tall? c. What are the genotypes and phenotypes? Check your work. Answers: a. 0% b. 100% c. 1 homozygous dominant: 1 heterozygous; 100% tall 2. If Mendel wanted to determine the genotype of a yellow round pea, what would be the best plant to cross it? a. GgWw b. GGWW c. ggWW d. GGww e. ggww Check your work. Answer is e. If the genotype of an individual is to be tested, the best cross to perform is the testcross, to a homozygous recessive. All of the other crosses will allow potential recessive alleles in the yellow round plant to remain masked. 3. What phenotypic ratio of offspring should be expected from the cross AaBb x AAbb? Check your work. Answer is d. Consider each gene separately. Aa x AA will only produce progeny with the A phenotype. Bb x bb is the testcross of a monhybrid, so will produce a 1:1 ratio. One class will have genotype AABb and AaBb and the other class will be composed of AAbb and Aabb individuals. 4. In hogs, a gene that produces a white belt (B) around the animal's body is dominant over its allele for a uniformly colored body (b). Another gene produces a fusion of the two hoofs on each foot, a condition known as syndactyly is mated with a female hog that is normal-footed and homozygous for the belted character. a. What are the genotypes of the male and female hog? b. What would be the phenotype ration? Check your work: Answers: a. male hot is bbTT b. female hog is BBtt c. phenotype is 16:0 all white belt syndactyly 5. Lauren, who has blood type AB, marries Sal who has type B blood but whose mother has type O. a. List the genotypes of Lauren, Sal and Sal's mother. b. What are the percent possibilities for the blood type of their offspring. Check your work: Answers: a. Lauren - IAIB, Sal - IBi, Sal's mother - ii b. 25% type AB, 25% type B, 25% type A, 25 % type B 6. In hamsters, rough coat (R) is dominant over smooth coat (r) and brown coat (B) is dominant over white coat(b). If you cross a homozygous rough, homozygous brown guinea pig with a smooth white one: a. What will be the genotypes of the parents? Check your work: Answer: a. RRBB x rrbb

More Punnett Square Problems 1. What is the maximum number of different phenotypes that could be produced by the mating of a blood type AB individual to a type B individual? a. 1 b. 2 c. 3 d. 4 2. One breed of cattle can be red, white, or roan. The cross between 2 roans produces equal number of red and white progeny and twice as many roans., If a farmer wanted to breed an all roan herd, what animals should be the parents? a. roan x roan b. red x red c. white x white d. red x white e. roan x red 3. One breed of cattle can be red, white, or roan. The cross between 2 roans produces equal number of red and white progeny and twice as many roans. If a farmer wanted to breed a half red and half roan herd, what animals should be the parents? a. roan x roan b. red x red c. white x white d. red x white e. roan x red 4. A cross between a purebred animal with red hairs and a purebred animal with white hairs produces an animal that has both red hairs and white hairs. What type of inheritance pattern is involved. a. incomplete dominance b. codominance c. multiple alleles d. polygenic traits 5. A red-flowered sweet pea plant is crossed with a whiteflowered sweet pea plant. All of the offspring are pink. What is the inheritance pattern being expressed? a. incomplete dominance b. codominance c. multiple alleles d. polygenic traits 6. The color of wheat grains shows a wide variability between red and white with multiple phenotypes. What type of inheritance patterns is being expressed? a. incomplete dominance b. codominance c. multiple alleles d. polygenic traits 7. Some people are able to roll their tongues into a U shape. The ability to do this is inherited as an autosomal dominant allele. What is the probability that children descendent from parents both heterozygous for this trait will be able to form a U shape with their tongues? a. O b. 25% c. 50% d. 75% 8. How many different allele combinations would be found in the gametes produced by a pea plant whose genotype was RrYY? a. 2 b. 4 c. 8 d. 16 9. If a pea plant that is heterozygous for round, yellow peas (RrYy) is crossed with a pea plant that is homozygous for round peas but heterozygous for yellow peas (RRYy), how many different henotypes are their offspring expected to show? a. 2 b. 4 c. 8 d. 16 10. Variation in human skin color is a result of a. incomplete dominance b. codominance c. polygenic traits d. multiple alleles 11. Situations in which one allele for a gene is not completely dominant over another allele for that gene are called a. multiple alleles b. incomplete dominance c. polygenic inheritance d. multiple genes 12. If roan cows and roan bulls are mated, according to the principle of codominance, ______% of the offspring are expected to be roan. 13. How many recessive alleles for a trait must an organism inherit in order to show that trait? 14. In dogs, short hair is dominant over long hair. If two heterozygous short-haired dogs are crossed, what percent of the offspring will have long hair? 15. In dogs, short hair is dominant over long hair. If a dog homozygous for short hair is crossed with a long hair dog, what percent of the offspring will have short hair? 16. Black color in horses is dominant over chestnut color. If a pure black horse is mated to a chestnut horse, what is the probability that the offspring will be chestnut colored? 17. A common recessive trait in dogs is deafness. A pure line of normal hearing dogs was crossed with a pure line of deaf dogs. F1 and F2 generations were produced. What % of the F1 generation is expected to have normal hearing?

18. What is the probability that a couple whose blood types are AB and O will have a type A child? 19. In a certain animal, black fur (B) is dominant over brown fur (b). If an animal heterozygous for black fur is crossed with an animal with brown fur, what % of the offspring will have brown fur? 20. In a species of chickens, incomplete dominance between alleles for black (B) and white(w) feathers is observed. Heterozygotes are blue. If two blue chickens are crossed, what is the probability that the offspring will be blue. 21. Freckles are dominant to no freckles. If Jack, who does not have freckles, marries Nicole who does, what % of their children will be recessive? 22. Cross Brian, who has blood type A blood but whose father is type 0, with Mary who has type AB blood. What % of their offspring may have B blood? 23. Lauren who has type A blood but whose mother has type B blood marries Ken who has type O. What % of their offspring will have O blood? 24. Crossing a pink-flowered four o’clock with a whiteflowered four o’clock will produce pink-flowered offspring and ___________-flowered offspring. 25. In snapdragons, the allele for tall plants is dominant to the allele for dwarf plants , and the allele for red flowers is codominant with the allele for white flowers . The heterozygous condition for flower color is pink. Question – If a dwarf red snapdragon is crossed with a white snapdragon homozygous for tall, what are the probable genotypes and phenotypes of the F1 generation? a. tall and pink b. tall and red c. tall and white d. dwarf and red e. dwarf and white 26. In fruit flies, the gene for curved wings (c) and the gene for spineless bristles (s) are on different chromosomes. (Normal wings = C and normal bristles = S) Question – From the cross CCSS x ccss, what is the probability of having an offspring that is CcSs? a. O b. 1/16 c. 3/16 d. 9/16 e. 1

27. Which of the following blood types are possible if the parents are A and O types? a. A and O b. B and O c. AB only d. O only e. A, B, and O 28. In guinea pigs, black is dominant. One half of a particular litter is white. The probable parent cross was: a. BB x Bb b. Bb x Bb c. Bb x bb d. bb x bb e. BB x bb 29. To determine whether an unknown black guinea pig is pure or hybrid black, it should be crossed with a. a white b. a hybrid black c. a hybrid white d. a pure black e. another unknown 30. Organisms that have two identical alleles for a particular trait are said to be a. hybrid b. homozygous c. heterozygous d. dominant 31. A pea plant heterozygous for height and seed color (TtYy) is crossed with a pea plant heterozygous for height but homozygous recessive for seed color (Ttyy). If 80 offspring are produced, how many are expected to be tall and have yellow seeds? 32. Heterozygous male guinea pigs with black, rough hair (BbRr) are crossed with heterozygous female guinea pigs with black, rough hair (BbRr). The incomplete Punnett square below shows the expected results form the cross. BR BBRR BBRr BbRR BbRr Br BBRr BBrr BbRr Bbrr bR BbRR BbRr X bbRr br BbRr Bbrr bbRr bbrr

BR Br bR br

Hair color B- black b-white Hair Texture: R-rough r-smooth What is the genotype of the offspring that would be represented in the square labeled X? 34. Identify the phenotype of the offspring represented in the square labeled X? 35. What is one of the possible genotypes for offspring with black, rough hair?

Essay Type Problems 1. A pea plant with yellow seeds was crossed with a plant with green seeds. The F1 generation produced plants with yellow seeds. Explain why green seeds reappeared in the F2 generation. 2. You wish to determine whether a tall pea plant is homozygous or heterozygous for tallness. What cross should you perform to arrive at your answer? Explain the cross of your choice. 3. Why are the result of genetic crosses shown in Punnett squares interpreted as probabilities, not certainties? Give some specific reasons. 4. A cross between two organisms heterozygous for two different genes (AaBb) results in a 9:3:3:1 phenotype ratio among the offspring. Is the offspring’s genotype ratio the same? Explain your answer. 5. Explain the difference between incomplete dominance and codominance. 6. A florist wants to guarantee that the seeds she sells will produce only pink-flowered four o’clock plants. How should she obtain the seeds? 7. Purple flowers are completely dominant in pea plants. How can you determine the genotype of a purple-flowering pea plant? Draw a Punnett square for each of the possible genotypes. 8. In tomatoes, red fruit color is dominant to yellow fruit color. Predict the genotypic ratio of offspring produced by crossing a homozygous dominant parent with a homozygous recessive parent. Draw a Punnett square to illustrate your prediction. 9. In pea plants, yellow seeds are dominant to green seeds. Predict the genotypic ratio of offspring produced by crossing two parents heterozygous for this trait. Draw a Punnett square to illustrate your prediction.

Even More Punnet Square Problems 1) A pea plant is heterozygous for both seed shape and seed color. S is the allele for the dominant, spherical shape characteristic; s is the allele for the recessive, dented shape characteristic. Y is the allele for the dominant, yellow color characteristic; y is the allele for the recessive, green color characteristic. What will be the distribution of these two alleles in this plant's gametes? A. 50% of gametes are Sy; 50% of gametes are sY B. 25% of gametes are SY; 25% of gametes are Sy;25% of gametes are sY; 25% of gametes are sy. C. 50% of gametes are sy; 50% of gametes are SY D. 100% of the gametes are SsYy E. 50% of gametes are SsYy; 50% of gametes are SSYY. 2) A phenotype ratio of 9:3:3:1 in the offspring of a mating of two organisms heterozygous for two traits is expected when: A. the genes reside on the same chromosome B. each gene contains two mutations C. the gene pairs assort independently during meiosis D. only recessive traits are scored E. none of the above 3) Which of the following genetic crosses would be predicted to give a phenotypic ratio of 9:3:3:1? A. SSYY x ssyy B. SsYY x SSYy C. SsYy x SsYy D. SSyy x ssYY E. ssYY x ssyy 4) The gametes of a plant of genotype SsYy should have the genotypes: A. Ss and Yy B. SY and sy C. SY, Sy, sY, and sy D. Ss, Yy, SY and sy E. SS, ss, YY, and yy 5) Which of the following genotypes would you not expect to find among the offspring of a SsYy x ssyy test cross: A. ssyy B. SsYy C. Ssyy D. ssYy E. SsYY 6) The expected phenotypic ratio of the progeny of a SsYy x ssyy test cross is: A. 9:3:3:1 B. 3:1 C. 1:1:1:1 D. 1:2:1 E. 3:1:1:3

7) In a dihybrid cross, AaBb x AaBb, what fraction of the offspring will be homozygous for both recessive traits? A. 1/16 B. 1/8 C. 3/16 D. 1/4 E. 3/4 8) Following a SsYy x SsYy cross, what fraction of the offspring are predicted to have a genotype that is heterozygous for both characteristics? A. 1/16 B. 2/16 C. 3/16 D. 4/16 E. 9/16 9) In a dihybrid cross, SsYy x SsYy, what fraction of the offspring will be homozygous for both traits? A. 1/16 B. 1/8 C. 3/16 D. 1/4 E. 3/4 10) If Mendel's crosses between tall, spherical-seeded plants and short, dented-seeded plants had produced many more than 1/16 short, dented-seeded plants in the F2 generation, he might have concluded that: A. the dented seed and short traits are unlinked. B. he would not have concluded any of the above. C. all traits in peas assort independently of each other. D. the spherical seed and tall traits are linked. E. all traits in peas are linked. 11) In Mendel's experiments, the spherical seed character (SS) is completely dominant over the dented seed character (ss). If the characters for height were incompletely dominant, such that TT are tall, Tt are intermediate and tt are short, what would be the phenotypes resulting from crossing a spherical-seeded, short (SStt) plant to a dented-seeded, tall (ssTT) plant? A. All the progeny would be spherical-seeded and tall. B. 1/2 would be spherical-seeded and intermediate height; 1/2 would be spherical-seeded and tall. C. All the progeny would be spherical-seeded and short. D. You cannot predict the outcome. E. All the progeny would be spherical-seeded and intermediate height.

12) Two unlinked loci effect mouse hair color. CC or Cc mice are agouti. Mice with genotype cc are albino because all pigment production and deposition of pigment in hair is blocked. At the second locus, the B allele (black agouti coat) is dominant to the b allele (brown agouti coat). A mouse with a black agouti coat is mated with an albino mouse of genotype bbcc. Half of the offspring are albino, one quarter are black agouti, and one quarter are brown agouti. What is the genotype of the black agouti parent? A. BBCC B. BbCc C. bbCC D. BbCC E. BBcc 13) Two unlinked loci effect mouse hair color. AA or Aa mice are agouti. Mice with genotype aa are albino because all pigment production is blocked, regardless of the phenotype at the second locus. At the second locus, the B allele (agouti coat) is dominant to the b allele (black coat). What would be the result of a cross between two agouti mice of genotype AaBb? A. 4 agouti: 4 black: 8 albino B. 9 agouti: 3 black: 3 albino: 1 grey C. 9 agouti: 3 black: 4 albino D. 8 agouti: 4 black: 4 albino

Sex-Linked Genes Problems 1) In a cross between a white-eyed female fruit fly and red-eyed male, what percent of the female offspring will have white eyes? (White eyes are X-linked, recessive) a. 100% b. 25% c. 50% d. 75% e. 0% 2) A female Drosophila of unknown genotype was crossed with a white-eyed male fly, of genotype (w = white eye allele is recessive, w+= red-eye allele is dominant.) Half of the male and half of the female offspring were red-eyed, and half of the male and half of the female offspring were white-eyed. What was the genotype of the female fly? a. b. c. d. e.

3) In a cross between a pure bred, red-eyed female fruit fly and a white-eyed male, what percent of the male offspring will have white eyes? (white eyes are X-linked, recessive) a. 100% b. 75% c. 50% d. 25% e. 0% 4) What is the genotype of a red-eyed, yellow-bodied female fruit fly who is homozygous for the eye color allele? Red eyes (w+) and tan bodies (y+) are the dominant alleles. (Both traits are X chromosome linked). a. b. c. d. e. 5) A white-eyed female fruit fly is crossed with a red-eyed male. Red eyes are dominant, and X-linked. What are the expected phenotypes of the offspring? a. All of the females will have red eyes; half of the males will have red eyes, and half of the males will have white eyes. b. All of the females and all of the males will have white eyes. c. All of the females will have red eyes; all of the males will have white eyes. d. All of the females and all of the males will have red eyes. e. All of the females will have white eyes; half of the males will have red eyes, and half of the males will have white eyes. 6) Hemophilia in humans is due to an X-chromosome mutation. What will be the results of mating between a normal (noncarrier) female and a hemophilac male? a. half of daughters are normal and half of sons are hemophilic. b. all sons are normal and all daughters are carriers. c. half of sons are normal and half are hemophilic; all daughters are carriers. d. all daughters are normal and all sons are carriers. e. half of daughters are hemophilic and half of daughters are carriers; all sons are normal.

7) A human female "carrier" who is heterozygous for the recessive, sex-linked trait causing red-green color blindness (or alternatively, hemophilia), marries a normal male. What proportion of their male progeny will have red-green color blindness (or alternatively, will be hemophiliac)? a. 100% b. 75% c. 50% d. 25% e. 0% 8) Women have sex chromosomes of XX, and men have sex chromosomes of XY. Which of a man's grandparents could not be the source of any of the genes on his Y-chromosome? a. Father's Mother. b. Mother's Father. c. Father's Father. d. Mother's Mother, Mother's Father, and Father's Mother. e. Mother's Mother. 9) Women have sex chromosomes of XX, and men have sex chromosomes of XY. Which of a women's grandparents could not be the source of any of the genes on either of her X-chromosomes? a. Mother's Father. b. Father's Mother. c. Mother's Mother. d. Father's Father. e. Mother's Mother and Mother's Father. 10) A human female "carrier" who is heterozygous for the recessive, sex-linked trait red color blindness, marries a normal male. What proportion of their female progeny will show the trait? a. All b. 1/2 c. 1/4 d. 0 e. 3/4


				
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