A Study on The Monohybrid Cross of Corn

Introduction

Mendelian Inheritance pattern was discovered by Gregor Mendel the “father of genetics”. His experiment observed various patterns of gene separation when combined with certain traits. He conducted his experiment with garden peas and was able to find the likeliness of a trait to reappear in future generations. The three principles Mendel founded were The Principle of Dominance and Excessiveness, Principle of Segregation, and the Principle of Independent Assortment. His theory lead to the understanding of genetic variation which is the differences between individuals or even large scale populations often influenced by mutations and sexual reproduction. The observations we can see on an individuals that makes them unique is describe as their phenotype or physical characteristics. Meanwhile, a person’s genotype can’t be observed directly but instead makes up one’s genetic information. When an organism is found to have the same alleles, they are referred to as being homozygous. If the organism has different alleles, they are classified as heterozygous where the dominant allele is expressed rather than the recessive trait. Punnet squares are used to find the probability of an organisms having the same alleles as its parents. Dominant homozygous, similar to homozygous, has the same copy of the same gene; however, a heterozygous dominant gene is made up of two different traits. Certain phenotypes such as having black hair are more common in certain populations because of the gene pool of those individuals have a higher probability of producing certain phenotypes. The variation of colors in corn are due to kernels having genes that are dominant, and are taken from natural selection. In lab we discussed studying two mono hybrid crosses: a cross of purple starchy with yellow starch. During a monohybrid cross of two heterozygous purple corn plants, the resulting phenotypes occur in a 3:1 ratio.

Materials and Methods

The materials used during the experiment is as followed:

• One ear of purple and yellow starch corn
• One blue marker
• One pen to record data

While working in groups of two, one person counted the number of kernels on the corn while the other recorded the data. We began with one column of kernels and counted vertically until we had a total of sixteen columns. Each kernel was marked with a blue marker so that a recount of the same row would not occur. After recording the data, we used the chi-square to determine if the numbers obtained fit a genetic cross predicted ratio. The probability used to determine whether the observed results were significantly different from the expected results goes as followed: The expected number of purple kernels should be determine by multiply the observed total by .75. To determine the number of expected yellow kernels, the observed total must be multiplied by .25.

The observed value for purple starchy was 3.6:1. Higher than what the expected value thought it would be at 3:1.

Discussion

The hypothesis stated that during a monohybrid cross of two heterozygous purple corn plants, the resulting phenotypes occur in a 3:1 ratio. This hypothesis has been well supported with the group and class ratios but equaling 3.6:1 ratio. The ear of corn we observed was a dominant heterozygous phenotype because the purple corn was the dominant trait compared to the yellow starchy color which would be consider recessive. The group data compared to the class data had the same observed ratio of purple starchy verse yellow starchy. The overall information collected by the class allows for a better and more extensive understanding of the corn species being handled in lab. Possible alternatives that may explain another hypothesis better than our own is genetic variation or a mutation in the particular piece of corn being used. Even though the observed ratios were the same, no two pieces of corn were alike which further sheds light on genetic diversity amongst organisms. Kernels that were yellow but had specks of purple on them were effected by transposable elements. Essentially, some genes are able to move on the chromosomes thus creating disruption in color on the kernel.

Conclusion

The information collected from this experiments not only supports the hypothesis but it has greater numbers than what was expected. The purple starchy kernels surpassed the 3:1 ratio and instead produced 3.6:1 ratio.