Introduction
Understanding the ways of predicting the chances of inheriting certain genetic traits makes up the value under the study of genetics. Such ability has enabled development of varieties of animals and plants that have most of the qualities that are a desirable prediction of inheritance patterns in family lineage. One of the methods that are used in determining the mathematical probability that a given trait would be inherited is the Punnett square. The Punnett square is a simple graphical method that is used to discover all the combinations of a given genotypes that can be passed to children in cases where parent genotypes are known (O'Neil, 2012).
This experiment aimed to explore how Punnett squares are employed in the prediction of the results of monohybrid genetic crosses. The prediction was achieved by constructing and analyzing Punnett Square for crosses using monohybrid genes scenarios that describe unique crosses of Drosophila.
Methods
The experiment was conducted using a virtual laboratory. The parents to cross were selected by clicking on the arrow near Parent 1 or Parent 2 and the button for checking parents clicked. The expected genotypes of the offspring were determined, and the Punnett square filled by clicking and dragging the appropriate genotypes at the bottom of the Punnett square to the appropriate boxes within the Punnett square. Given the genotypes of the offspring, the phenotypes of the offspring were determined, and the Punnett square filled by clicking and dragging the appropriate phenotypes at the bottom of the Punnett square. The check offspring button was clicked to check for the correct combinations. Data was recorded, and the experiment repeated twice using different scenarios.
Results
The results for the genotypes and phenotype ratio of the offspring from the selected scenarios were recorded in Table 1 below. Different parent genotype combinations resulted in different ratios in the genotype and phenotypes of the offspring.
Discussion
A combination of heterozygous parent with a homozygous one resulted in a ratio of 1:1 both in genotype and phenotype. A combination of parents who were both heterozygous resulted in offspring who had all the three possible genotypes and only two different phenotype. On the other hand combining a homozygous dominant parent with a homozygous recessive one resulted in offspring with similar genotype and phenotype.
Questions
- The phenotype ratio may be used calculate the percentage of offspring that show each trait by dividing the number of similar traits into the square by 4 and then multiplying by 100.
- It is difficult to determine the genotype for a gray-bodied fly considering that gray allele is dominant over the black allele. The possible genotypes include GG and Gg.
- This results from the suppression of the recessive gene by the dominant one causing organisms with heterozygous genotypes to express the dominant allele only.
- Punnett square provides information for the inheritance from discrete genetic traits and thus able to predict the offspring characteristics from such traits. It is however unable to provide information for the phenotypes that result from the gene interactions that cannot be reduced to individual genetic components.
Conclusion
Punnett square had proved to be a valuable tool in the prediction of the probabilities of offspring’s genotype and phenotypes given the genotypes of their parents.
References
O'Neil, D. (2012). Probability of Inheritance. Retrieved December 14, 2014, from http://anthro.palomar.edu/mendel/mendel_2.htm
