1. Monohybrid and DihybridCross Submitted by: ARIOLA, Inah Abbygail T.VERA, Dianne Eliza G.

2. Monohybrid cross 3. Monohybrid Cross a method of determining the inheritance patternof a trait between two single organisms. a cross between parents who are true-breedingfor a trait; i.e., both are homozygous for one alleleof thegene, for example AA x aa, inwhich A is the dominant allelefor a trait and a is the recessiveallele for that same trait. 4. Sample Problem In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds? 5. Analysis The figure above represents a monohybridcross of F1-hybrid plants. Both parent plants are heterozygous (Ss) foran allele that determines seed shape. Presence of the dominant allele (S) inhomozygous (SS) or heterozygous (Ss) plantsresults in spherical seeds. Homozygous recessive (ss) plants havedented seeds. 6. Analysis To solve the sample problem, youll need to set up a Punnett square. Punnett square - a diagram that is used to predict an outcome of a particular cross or breeding experiment 7. Steps to Solve the SampleProblem Set up a 2 by 2 Punnett square. 8. Steps to Solve the SampleProblem Write the alleles for parent 1 on the left side of the Punnett square. Each gamete will have one of the two alleles of S the parent. In this particular cross, half of the gametes will have the dominant (S) allele,s and half will have the recessive (s) allele. We will use blue and brown to keep track of the alleles of each parent. 9. Steps to Solve the SampleProblem Write the alleles from parent 2 aboveS s the Punnett square. For this heterozygous parent (Ss), half of the S gametes will have the dominant (S) allele, and half will have the recessive (s) allele.s 10. Steps to Solve the SampleProblem Fill the squares for parent 1. S s Fill each square with the allele from Parent 1 that lines up with the row.S SS S s Fill the squares for parent 2.s Ss ss Fill each square with the allele from Parent 2 that lines up with the column. 11. Steps to Solve the SampleProblem Interpreting the results of a PunnettS s square Genotypes that resulted from this monohybrid crossS SS S s (Ss x Ss) 25% homozygous dominant s Ss ss 50% heterozygous 25% homozygous recessive 12. Steps to Solve the SampleProblem Interpreting the results of a PunnettS s square Phenotypes that resulted from this monohybrid crossS SS S s (Ss x Ss) 75% Spherical 25% Dented s Ss ss 13. Dihybrid cross 14. Dihybrid Cross a cross between F1 offspring (first generationoffspring) of two individuals that differ in two traitsof particular interest. used to test for dominant and recessive genes intwo separate characteristics The rules of meiosis, as they apply to thedihybrid, are codified in Mendels First Law andMendels Second Law, which are also called theLaw of Segregation and the Law of IndependentAssortment, respectively 15. Example Problem In summer squash, white fruit color (W) is dominant over yellow fruit color (w) and disk- shaped fruit (D) is dominant over sphere- shaped fruit (d).. If a squash plant true- breeding for white, disk-shaped fruit is crossed with a plant true-breeding for yellow, sphere-shaped fruit, what will the phenotypic and genotypic ratios be for: a. the F1 generation? b. the F2 generation? 16. Steps to Solve the SampleProblem Write down the cross in terms of the parental (P1) genotypes and phenotypes: WWDD (white, disk-shapedfruit) X wwdd (yellow, sphere-shaped fruit) 17. Steps to Solve the SampleProblem Determine the P1 gametes, place them in a Punnett Square and fill in the resulting genotypes: 18. Steps to Solve the SampleProblem Determine the genotypic and phenotypic ratios for the F1 generation: All F1 progeny will beheterozygous for both characters(WwDd) and will have white, disk-shaped fruit . 19. Steps to Solve the SampleProblem Write down the cross between F1 progeny: WwDd (white, disk-shapedfruit) X WwDd (white,disk-shaped fruit) 20. Steps to Solve the SampleProblem Determine the F1 gametes, place them in a Punnett Square and fill in the resulting genotypes: 21. Steps to Solve the SampleProblem Determine the genotypic and phenotypic ratios for the F2 generation: Genotypic ratios: 1/16 will be homozygous dominant for both traits (WWDD) 2/16 will be homozygous dominant for color and heterozygous for shape (WWDd) 2/16 will be heterozygous for color and homozygous dominant for shape (WwDD) 1/16 will be homozygous dominant for color and homozygous recessive for shape (WWdd) 4/16 will be heterozygous for both traits (WwDd) 22. Steps to Solve the SampleProblem 2/16 will be heteozygous for color and homozygous recessive for shape (Wwdd) 1/16 will be homozygous recessive for color and homozygous dominant for shape (wwDD) 2/16 will be homozygous recessive for color and heterozygous for shape (wwDd) 1/16 will be homozygous recessive for both traits (wwdd) This is a 1:2:2:1:4:2:1:2:1 genotypic ratio 23. Steps to Solve the SampleProblem Determine the genotypic and phenotypic ratios for the F2 generation: Phenotypic ratios: 9/16 will have white, disk-shaped fruit 3/16 will have white, sphere-shaped fruit 3/16 will have yellow, disk-shaped fruit 1/16 will have yellow, sphere-shaped fruit This is a 9:3:3:1 phenotypic ratio.