Practice Problems of Biology

Practice Problems! Set up the square for each of the crosses listed below. The trait being studied is round seeds (dominant) and wrinkled seeds (recessive). Remember to show all work! 1   1. Rr x rr Punnett Square: | R | r | --- | --- | --- | r | Rr | rr | r | Rr | rr | What percentage of the offspring will be round? 50% Rr x Rr Punnett Square: | R | r | --- | --- | --- | R | RR | Rr | r | Rr | rr | What percentage of the offspring will be round? 75% RR x Rr Punnett Square: | R | R | --- | --- | --- | R | RR | RR | r | RR | Rr | What percentage of the offspring will be round? 100% 4. A TT (tall) plant is crossed with a tt (short plant). * Punnett Square: * | T | T | * --- | --- | --- | * t | Tt | Tt | * t | Tt | Tt | What % of the offspring will be tall? 100% 5. A Tt plant is crossed with a Tt plant. * Punnett Square: * | T | t | * --- | --- | --- | * T | TT | Tt | * t | Tt | tt | What % of the offspring will be short? 25% 6. A heterozygous round seeded plant (Rr) is crossed with a homozygous round seeded plant (RR). 1   1. www.oxfordasd.org www.oxfordasd.org * Punnett Square: * | R | r | * --- | --- | --- | * R | RR | Rr | * R | RR | Rr | What % of the offspring will be homozygous (RR)? 50% 7. A homozygous round seeded plant is crossed with a homozygous wrinkled seeded plant. * Parent genotypes: RR x rr * Punnett Square: * | R | R | * --- | --- | --- | * r | Rr | Rr | * r | Rr | Rr | What % of the offspring will be homozygous? 0% 8. In pea plants, purple flowers are dominant to white flowers. * Complete a cross for two white colored plants. * Parent genotypes: pp x pp * Punnett Square: * | p | p | * --- | --- | --- | * p | pp | pp | * p | pp | pp | What % of their offspring will be white flowered? 100% 9. A white flowered plant is crossed with a plant that is heterozygous for the trait. * Punnett Square: * | P | p | * --- | --- | --- | * P | PP | Pp | * p | Pp | pp | What % of the offspring will have purple flowers? 50% 10. Two plants, both heterozygous for the gene that controls flower color are crossed. * Punnett Square: * | P | p | * --- | --- | --- | * P | PP | Pp | * p | Pp | pp | What % of their offspring will have purple flowers? 75% What % will have white flowers? 25% 11. In guinea pigs, the allele for short hair is dominant. * What genotype would a heterozygous short haired guinea pig have? Ss * What genotype would a homozygous short haired guinea pig have? SS * What genotype would a long haired guinea pig have? ss 12. Show the cross for a pure breeding short haired guinea pig and a long haired guinea pig. 1   1. * Punnett Square: * | S | S | * --- | --- | --- | * s | Ss | Ss | * s | Ss | Ss | What % of the offspring will have short hair? 100% 13. Show the cross for two heterozygous guinea pigs. * Punnett Square: * | S | s | * --- | --- | --- | * S | SS | Ss | * s | Ss | ss | What % of the offspring will have short hair? 75% What % of the offspring will have long hair? 25% 14. CHALLENGE! Two short haired guinea pigs are mated several times. Out of 100 offspring, 25 of them have long hair. What are the probable genotypes of the parents? * Ss x Ss Show the cross to prove it! * Punnett Square: * | S | s | * --- | --- | --- | * S | SS | Ss | * s | Ss | ss |