It is also possible to analyze the dihybrid cross with a Punnett\'s square. For

Question

It is also possible to analyze the dihybrid cross with a Punnett's square. For a dihybrid cross, we'll need a 4 x 4 grid because there are four genotypes in the Fi gametes. Here is the Punnett's square analysis of the Fi cross from the above example. F1 cross- Rr Tt x Rr Tt R T r T RR Tt Rr TT Rr Tt R T RR Tt Rr Tt Rr tt Rt IL rr Tt r t Rr Tt Rr tt rr Tt 16) Using what you have learned about Mendel's law of random segregation and independent assortment, why are all possible combinations of genes used in the dihybrid Punnett's square? In other words, along the top and side of the above Punnett's square, every possible combination of genes from each of the parents (Fi) is represented. Why is this necessary? What does it account for? 17) What are the phenotypic and genotypic ratios of the F2 offspring from the above crosses? 18) Construct a dihybrid Punnett's from the above example. What are the phenotypic ratios of the F2 offspring? square for Fi parents with genotypes different (your choice) 19, n front of you there is offspring (#3) from the F1 parents of a dihybrid cross. Using a chi uare test, and what you have learned about Mendel's laws, determine the genotype and phenotypes of the Fi parents. To answer this question properly, you will need to construct a chi-square table and determine your expected and observed values for each phenotype. In addition you need to correctly identify your null and alternative hypotheses when conducting the chi-square test

Explanation / Answer

Null hypothesis (H0): There is no significant difference between observed and expected frequencies. genes are unlinked

Alternative hypothesis (H1): There is a significant difference between observed and expected frequencies genes are linked.

Round tall = 701

Round dwarf = 204

Wrinkle tall = 243

Wrinkle dwarf = 68

degree of freedom is 3

Table value for chi square is = 7.815

Chi square Table value > observed chi square value.

So, null hypothesis accepted

Observed Expected (O-E) O-E)2 / E Round tall 701 1216 * 9/16 = 684 17 0.42 Round dwarf 204 1216 * 3/16 = 228 -24 2.53 Wrinkle tall 243 1216 * 3/16 = 228 15 0.99 Wrinkle dwarf 68 1216 * 1/16 = 76 -8 0.84 Total 1216 4.76

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