Lab Report: Genetic Crosses 1

Question

Apply your understanding of how alleles assort and combine during reproduction to evaluate a scenario involving a monohybrid cross.

The allele for having freckles (F) is dominant over the allele for not having freckles (f). Some characteristics in people are inherited as simple dominant and recessive traits. One example is freckles. Freckles is a dominant trait, and the lack of freckles is a recessive trait. In this example, a person with freckles is represented as either FF or Ff, and a person with no freckles is represented as ff.

  Imagine a mother and a father who both have freckles and are heterozygous for the trait, or Ff. They are the P generation, or parent generation. Create a Punnett square to show their offspring, the F1 generation.

Answer 1

Set up a Punnett square by making a 2 X 2 grid, put the symbols for two alleles from from one parent as the headings for each of the two columns and the two alleles from the other parent as the headings for each of the two rows. Put the symbol from the column heading and the row heading together into each of the 4 boxes. This will show the possible outcomes of the cross.

Here, the trait of having freckles is dominant so it is represented by the capital letter F and the trait of no freckles is recessive so it is represented by a lower case f. So the heading of the first column and first row are both F and the second column and second row are both f. In this case the two parents are heterozygous (meaning they carry both alleles) so their genotypes are the same, both are Ff. Our grid ends up with FF in the upper left, Ff in the upper right, Ff in the lower left and ff in the lower right.