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Genetics B Patrick McClanahan Jill Farinsky Jesse Chen Matt Kang.

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Presentation on theme: "Genetics B Patrick McClanahan Jill Farinsky Jesse Chen Matt Kang."— Presentation transcript:

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. <- Answer B. G1, G2. C. parental, F2. D. F2, parental. E. P1, P2


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