Lab Repor t Name: _______________________
Exercise 1 – The Punnett Square
- Write a hypothesis describing the phenotype of the germinating tobacco seeds. Include the approximate number of seedlings and percentages that will have a dominant trait and recessive trait out 50 seeds.
- Create a Punnett square using Data Table 1, showing the possible F2 generation outcomes from a cross between a heterozygous male and a heterozygous female for the germinating tobacco seeds. The dominant allele is written as “G” for green and the recessive allele for albino/yellow color is written as “g”.
Data Table 1: Hypothetical Punnett Square
Father ( ____ ____ ) x Mother ( ____ ____)
- Count the number of seedlings that are green versus those that are yellow and record the data in Data Table 2.
Data Table 2 – Seedling data
Number of Seedlings
Percentage of Total
- Compare the expected outcome to actual results found in Data Table 2, write this information into Data Table 3.
Data Table 3 – Frequency calculations
- What are the predicted ratios of the phenotypes (green to yellow) in the plants?
- What were the actual ratios of the phenotypes (green to yellow) displayed in the tobacco plants?
- If all yellow seedlings were removed from the population, would the next generation still have a chance at displaying the yellow allele? Explain your answer.
- Would a cross between a homozygous and a heterozygous parent show the same ratios?
- Explain why it may be important to collect data from a larger population.
Exercise 2 – Dihybrid Crossing with Corn
- Count the number of purple, yellow, smooth and wrinkled seeds on the ear of corn between the lines in Figures 4-7 and record the data in Data Table 4.
Data Table 4 – Corn kernel data
Number of Kernels
Kernel Percentage (divide count by total, then multiply by 100)
- The ear of corn is a result of a cross between plants that were both heterozygous for color and texture. Write the genotypes of both parents of this dihybrid cross. (P = purple color; p = yellow color; S = smooth shape; s = wrinkled shape)
- What are the possible gametes for both parents? (Place these gametes into the Punnett square in Data Table 5 for both the male and the female.)
- Calculate the phenotypic ratios that are expected for each type of seed.
- Purple & smooth ______________________
- Purple & winkled _____________________
- Yellow & smooth _____________________
- Yellow & wrinkled ____________________
Data Table 5 – Punnett square for dihybrid cross
Parent Gametes ♂
Parent Gametes ♀
- Calculate the expected percentage of:
- Purple, smooth kernels ________________________
- Purple, wrinkled kernels _______________________
- Yellow, smooth kernels ________________________
- Yellow, wrinkled kernels _______________________
- Count the number of purple/smooth; purple/wrinkled; yellow/smooth and yellow/wrinkled kernels on the quarter ear of corn and record the numbers in Data Table 6.
Data Table 6 – Data from corn kernels
Ratio: Number counted/total
Purple and smooth
Purple and wrinkled
Yellow and smooth
Yellow and wrinkled
What are the probable coloration phenotypes of the corncob parents?
- What are the probable texture phenotypes of the corncob parents?
- Was the ratio calculated in Data Table 6 equal to 9:3:3:1? If not, given a possible explanation as to why not.