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Genetics B

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.

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Genetics B

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  1. Genetics B Patrick McClanahan Jill Farinsky Jesse Chen Matt Kang

  2. 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

  3. Pictures of monohybrid

  4. Pictures of dyhibrid

  5. 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.

  6. 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.

  7. 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.

  8. Why you use monohybrid croses • You use monohybrid crosses so you can predict the phenotype and the genotype for your offspring.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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

  14. 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

  15. 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.

  16. 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. <- AnswerB. G1, G2.C. parental, F2.D. F2, parental.E. P1, P2

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