1. Explain why it's unknown which of two alleles an offspring will obtain from its biological mother or father for a given characteristic. 2. Reginald Punnett sought to apply the insights obtained by Mendel to explain the laws of inheritance in a structured fashion. What's a Punnett square and how is it used? 3. You're conducting a science experiment crossing two different purebred mouse strains, which each contain a different variation of the same gene, for two generations. What do you expect to see as the phenotypes of the first generation? The second generation? 4. How closely do Mendel's insights into dominant and recessive traits match up with the ratios that Punnett calculated in his Punnett squares?

4. Each parent organism contributes one copy of its alleles in a seemingly random fashion to its offspring, as meiosis to create gametes (egg or sperm cells) reduces the number of genes by half.

5. Therefore, each gamete contributes only one allele. A Punnett square is a diagram used to map out the possible genotypes of a child given the genotypes of its parents. In a Punnett square, the genotype of one parent is listed in the first row of the square, and the genotype of the second parent is listed in the first column. Then, in the middle squares, all possible genotypes of their offspring are listed, and the phenotypes are calculated using the law of dominance.

6. Purebred strains of organisms always produce heterozygous offspring in the first generation, with all members of the first generation exhibiting the dominant trait for the gene of interest. The second generation typically has a 3:1 mix of dominant and recessive phenotypes, respectively.

7. Punnett squares predict that the second generation of two distinct purebred homozygotes for a trait will have a 3:1 ratio of dominant to recessive traits. Mendel did careful statistical analysis on his hybridization experiments and found that, for each of his seven characteristics of interest, the ratio was approximately, but not exactly, 3:1. Therefore, Mendel's experimental observations match the predictions of Punnett squares quite well.

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