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Genetics B Patrick McClanahan Jill Farinsky Jesse Chen Matt Kang Definitions • Monohybrid: off springof parents that differ in only one genetic characteristic. Usually imples heterzygosity at a single locus under study. • Dihybrid: a cross between two individuals that are hetrozygos at two loci for example, AaBb/AaBb Pictures of monohybrid QuickTime™ and a decompressor are needed to see this picture. QuickTime™ and a decompressor are needed to see this pict ure. Pictures of dyhibrid QuickTime™ and a decompressor are needed to see this picture. Vocabulary • • • • • • • • Punnett Square: the gene combinations that might result from a genetic cross can be determined by drawing a diagram. Homozygous: organisms that have two identical alleles for a particaular trait. Heterozygous: organisms that have two different alleles for the same trait. Phenotype: physical characteristics. Genotype: genetic make up. Independent assortment: alleles for seed shape segregate independently of those for seed color. Incomplete dominance:cases in which one allele is not completely dominant over another. Co-dominance: in which both alleles contribute to the phenotype. How to do a monohybrid cross • To do it you draw a square and devide it in to four parts. • Then you write the parents traits one above each box on the top and on the side. • Then you combine the letters in to all four box’s to see what your children will look like. How to do a dihybrid cross • Foial the four letters and then make a 16 square box instead of a 4 square box. • Then you write the four letters above and on the top and the side • Then you combine the letters in all of the 16 boxes. Why you use monohybrid croses • You use monohybrid crosses so you can predict the phenotype and the genotype for your offspring. Why do you use a dyhibrid crosses • You use dyhibrid crosses for the same reason you would use monohybrid crosses except with dyhibrid you are trying to determine 2 different traits. Intersting facts about monohybrid and dihybrid crosses • Monohybrid and dihybrid crosses can be used to determine traits for any organism. • Each square in a monohybrid cross is 25% total. • Different combinations of alleles can be considered multiple alleles Interesting facts cont. • Capital letters represent dominant traits, and lowercase letters represant ressessive traits. • Some alleles are nither dominant or ressive. • Many traits are controlled by multiple alleles or multiple genes. Questions • 1. Monohybrid crosses use a punnet square with how many sections A:2 B:4 C:6 D:8 • 2.Dihybrid crosses involve how many traits? A:1 B:2 C:3 D:4 • 3.Do monohybrids and dyhybrid crosses show genotypes or phenotypes? A: Genotype B: Phenotype C:both D:nither • 4. True of False: dihybrid crosses are more common then monohybrid crosses? • 5. How many squares are used in a punnet square when it’s a dihybrid cross? A:16 B:20 C:4 D:18 • 6. True or false: before you write out the letters across the top or side of the punnet square for a dihybrid cross you foial the four letters for each organism. • • 7. True or false: every trait is represented by two letters. 8. True or false: if the parents both have all recessive, what is the chance that the off sprong will have a dominant trait A:0% B:25% C:50% D:75% • 9. What is monohybrid • 10. What is dihybrid • 11. 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 chromosomeB. each gene contains two mutationsC. the gene pairs assort independently during meiosis <- AnswerD. only recessive traits are scoredE. none of the above • 12. Which of the following genetic crosses would be predicted to give a phenotypic ratio of 9:3:3:1?A. SSYY x ssyyB. SsYY x SSYyC. SsYy x SsYy <- AnswerD. SSyy x ssYYE. ssYY x ssyy • • • 13. The gametes of a plant of genotype SsYy should have the genotypes:A. Ss and YyB. SY and syC. SY, Sy, sY, and sy <- AnswerD. Ss, Yy, SY and syE. SS, ss, YY, and yy 14. Which of the following genotypes would you not expect to find among the offspring of a SsYy x ssyy test cross:A. ssyyB. SsYyC. SsyyD. ssYyE. SsYY <- Answer 15. The expected phenotypic ratio of the progeny of a SsYy x ssyy test cross is:A. 9:3:3:1B. 3:1C. 1:1:1:1 <- AnswerD. 1:2:1E. 3:1:1:3 16. A phenotypic ratio of 3:1 in the offspring of a mating of two organisms heterozygous for a single trait is expected when: •A. the alleles segregate during meiosis. <- Answer •B. each allele contains two mutations. •C. the alleles are identical. •D. the alleles are incompletely dominant. •E. only recessive traits are scored. 17. A genetic cross between two F1-hybrid pea plants having yellow seeds will yield what percent green-seeded plants inthe F2 generation? Yellow seeds are dominant to green. A. 0% B. 25% <- Answer C. 50% D. 75% E. 100% 18. When true-breeding tall stem pea plants are crossed with true-breeding short stem pea plants, all of the _________ plants, and 3/4 of the __________ plants had tall stems. Therefore, tall stems are dominant. A. F1, F2. <- Answer B. G1, G2. C. parental, F2. D. F2, parental. E. P1, P2 19. To identify the genotype of yellow-seeded pea plants aseither homozygous dominant (YY) or heterozygous (Yy), you could do a test cross with plants of genotype _______. A. y B. Y C. yy <- Answer D. YY E. Yy 20. What are the possible blood types of the offspring of a cross between individuals that are type AB and type O? (Hint: blood type O is recessive) A. AB or O B. A, B, or O C. A o r B <- Answer D. A, B, AB , or O E. A, B, or AB