Biology

Biology

Lab Repor t Name: _______________________

Section: _____________________

4

Plant Genetics

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 ( ____ ____)

Mother ♀

Father ♂

Gametes

  • 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

Seedling Color

Green

Yellow

Total

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

Frequency

Expected Values

Actual Values

Green

Yellow

Total

Questions:

  • 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)

Kernel Coloration

Purple

Yellow

TOTAL

Kernel Texture

Smooth

Wrinkled

TOTAL

  • 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 ♂

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

Number Counted

Ratio: Number counted/total

Purple and smooth

Purple and wrinkled

Yellow and smooth

Yellow and wrinkled

TOTAL

Questions

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.

 

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