Plant Genetics

Plant Genetics

Abstract

In the first exercise I grew tobacco seeds in a Petri dish. I also created a Punnett Square to show the possible outcomes from a cross between heterozygous males and heterozygous females and used the data to determine a hypothesis on the approximate number of seedlings that will have dominant(green) and recessive (yellow) traits out of the 50 seedlings. After the seeds germinated I observed how many were green and how many were yellow and recorded the data in Table 2. I then compared the actual results to my predicted results. In the second exercise I observed pictures of an ear of corn to determine the type of cross responsible for color and texture of corn kernels. I counted the individual kernels that were purple, yellow, smooth, and wrinkled separately and recorded the data in Table 4. I then created a punnett square for dihybrid cross using heterozygous dihybrid gametes represented by PpSs for both the male and female. I used the information from the Punnett square to calculate expected phenotypic ratios of each type of seed. I then counted the number of each (purple & smooth, purple & wrinkled, yellow & smooth, yellow & wrinkled) and recorded the data in Table 6 and compared the estimated data to the actual data to see how close they were to each other.

Introduction

The purpose of the experiments is to help us learn to predict genetic frequency of offspring in monohybrid crosses as well as how to use the Punnett square in helping predict outcomes of genetic crosses. We also learned how to analyze the results of a genetic cross.

Hypothesis

My hypothesis for experiment one was that about 75% of the seedlings will be green and 25% of them will be yellow.

Procedure

In the first exercise I used a Petri dish, paper towel, tobacco seeds, water, and magnifying glass. I cut the paper towel to fit in the Petri dish and moistened it with water. I then sprinkled the tobacco seeds onto paper towel, placed the Petri dish in a window with indirect light, and observed for germination. After the seeds germinated I observed the sprouts and recorded the data in Table 2 and compared my actual results to the predicted results from my Punnet square.

In the second exercise I observed pictures of ears of corn and counted the different colors and shapes of the kernels (purple, yellow, and smooth, wrinkled) from each of the 4 pictures. I recorded my observations in Table 4 and then constructed a Punnett square for dihybrid cross using heterozygous plant gametes. These parents were written as PpSs for both the male and the female. I calculated the phenotypic ratios that are expected by using the information from the Punnett square. I then counted the number of each type of seed (purple & smooth, purple & wrinkled, yellow & smooth, yellow & wrinkled) in the picture and recorded that data in Table 6. After that I compared my actual results to the predicted results from the Punnett square.

Results

Data Table 1: Punnett square.

Father ( G g )X Mother( G g )

Father

Gametes

G

g

G

GG

Gg

g

Gg

gg

Mother

Data Table 2: Seedling data.

Seedling Color

Green Yellow Total

Number of

Seedlings 18 11 29

Percentage of

Total 62% 38% 100%

Data Table 3: Frequency calculations.

Frequency Expected

Values

Actual Values

Green 75% 62%

Yellow 25% 38%