Name: Per. Date: Monohybrid Cross Punnett Square Problems Monohybrid Crosses (only one trait) Exhibiting Complete Dominance Example: Brown hair is dominant over yellow hair. A heterozygous brown haired female and a homozygous yellow haired male mate and want to know the possibility of having yellow haired children. Show the square for this cross. List the genotypes and phenotypes of the children and the ratio of each. Trait: Phenotypes: Alleles (key): Parent Genotypes: x Punnett Square: Children Genotypes and Ratio: Children Phenotypes and Ratio: 1. A homozygous black cat is crossed with a homozygous white cat and they have a litter of kittens. Assuming that the trait for black hair is dominant, give the cross, the genotypes and their ratios, and the phenotypes and their ratios for their offspring. Use the letter B/b for this cross. Trait: Phenotypes: Alleles (key): Parent Genotypes: x Punnett Square: Children Genotypes and Ratio: Children Phenotypes and Ratio: 1
2. Hitchhiker s thumb is a recessive trait. If a man with a hitchhiker s thumb mates with a woman who is heterozygous for this trait: a. Write the genotypic cross b. Draw a Punnett square for this cross c. Determine the genotypic ratios d. Determine and phenotypic ratios 3. In sheep, white wool (B) is dominant over black wool (b). Two heterozygous sheep are crossed. What fraction of the white lambs are heterozygous? 4. Widow s peaks are dominant. A woman who has a widow s peak and a man who has a widow s peak have a child. a. What are the possible genotypes of the man and woman? b. Draw the possible Punnett squares. c. The child does not have a widow s peak. Circle the Punnett Square that could show this result. d. What are the genotypes of the parents? 2
5. Brown eyes are dominant to blue eyes a. Could two blue-eyed people have a brown-eyed child? Explain using a Punnett square. b. Mary has blue eyes, but both her mom and dad have brown eyes. What are the chances that a child in this family will have blue eyes? Brown eyes? Explain using a Punnett square. 6. A baby without dimples (dimples are dominant) has a mom that doesn t have dimples and a dad that does have dimples. What must the genotypes of the parents be? 7. Sickle cell disease is caused by a defect in the coding for the amino acid sequence of hemoglobin. Heterozygous people appear normal, but when their blood is held under low oxygen concentrations, the red blood cells become sickle-shaped. A young woman has a brother who dies of sickle cell disease and she is concerned about the chance of the condition appearing in her children. When blood samples are taken and placed under low oxygen concentration, her red blood cells become sickled, but those of her prospective husband remain normal. a. What are the genotypes of the woman and her prospective husband? b. With their genotypes, make a Punnett square. c. What is the probability of their children having sickle cell disease? 3
Monohybrid Crosses Exhibiting Codominance or Incomplete Dominance 8. Explain the difference between incomplete dominance and codominance: 9. In some chickens, the gene for feather color is controlled by codiminance. The allele for black is B and the allele for white is W. The heterozygous phenotype is known as erminette a. What is the genotype for black chickens? b. What is the genotype for white chickens? c. What is the genotype for erminette chickens? 10. If two erminette chickens were crossed, what is the probability that: a. They would have a black chick? % b. They would have a white chick? % 11. A black chicken and a white chicken are crossed. What is the probability that they will have erminette chicks? % 12. In snapdragons, flower color is controlled by incomplete dominance. The two alleles are red (R) and white (W). The heterozygous genotype is expressed as pink. a. What is the phenotype of a plant with the genotype RR? b. What is the phenotype of a plant with the genotype WW? c. What is the phenotype of a plant with the genotype RW? 4
13. A pink-flowered plant is crossed with a white-flowered plant. What is the probability of producing a pink-flowered plant? % 14. What cross will produce the most pink-flowered plants? Show a punnett square to support your answer. Monohybrid Crosses Exhibiting Multiple Alleles 15. Human hair color is controlled by one gene with four alleles (with some incomplete dominance): Alleles: HBr = brown HBd = blonde hr = red hbk = black The possible genotypes and phenotypes: HBdHBd or HBdhbk = blonde HBdHBr = mousy brown HBdhR = strawberry blonde HBrHBr or HBr hbk = brown HBrhR = auburn hrhr or hrhbk = red hbkhbk = black a. What do you think your parent s phenotypes and genotypes for hair color are? b. What are your phenotype and genotype for hair color? c. If someone with auburn hair has children with someone with red hair (but whose mother had black hair), what are the genotype and phenotype probabilities for their children? 5
16. Blood type is controlled by one gene with three alleles (and some with codominance) Allele Codes for: Genotype Phenotype (blood type) I A A protein on RBC I A I A Type A I B B protein on RBC I A i Type A I No protein I B I B Type B I B i Type B I A I B Type AB ii Type O a. A woman with Type O blood and a man who is Type AB have are expecting a child. What are the possible blood types of the kid? b. What are the possible blood types of a child who's parents are both heterozygous for "B" blood type? c. What are the chances of a woman with Type AB and a man with Type A having a child with Type O? d. Jill is blood Type O. She has two older brothers (who tease her like crazy) with blood types A & B. What are the genotypes of her parents with respect to this trait? e. A test was done to determine the biological father of a child. The child's blood Type is A and the mother's is B. Dude #1 has a blood type of O, & dude #2 has blood type AB. Which dude is the biological father? 6