Lab Report: Genetic Crosses 1

Question

   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.

F f

F FF Ff

f Ff ff                                

Calculate the ratios of the genotypes and phenotypes of the offspring in the F1 generation.

Genotypes:

Phenotypes:

Answer 1

The most important concept involved in being able to answer this question is understanding the difference between genotype and phenotype.

GENOtype- the genetic constitution of an organism (basically what genes the organism has at a molecular level)

PHENOtype- the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment (basically what the organism looks like)

In this particular cross there are three possible genotypes as seen on the punnet square; FF, Ff, and ff. The ratio of these genotypes is 1:2:1 (FF:Ff:ff). However, there are only two possible phenotypes. This is due to the concept of dominant alleles. A dominant allele is an allele which is expressed. A recessive allele/gene is only expressed in the absence of a dominant allele. The genotypes FF and Ff will both present the dominant phenotype since they each contain at least one dominant allele. The genotype ff will present the recessive phenotype since there is no dominant allele. The ratio of these phenotypes is 3:1.

Remember, dominant alleles are represented by a capital letter, and recessive alleles are represented by a lowercase letter.