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Biology 12 Lab
Genetics of Corn Lab
Corn is one of the world’s most important food crops. It has been subject to selective
breeding techniques and hybridization for many years, which have resulted in
vigorous, high-yielding varieties. Nearly all corn grown today is hybrid corn. Some
varieties of corn are chosen for their sweet flavour while the mixed coloration of
the Indian corn varieties makes them popular decorations during the autumn
months.
In this activity, you will determine the probable genotypes of parents by examining
the phenotypes of corn for two different and independently assorted traits.
Purpose: To investigate the inheritance of traits using corn.
Materials : dihybrid corn ears (sample A, sample B)
Sample A
Procedure/Observations:
1. Obtain a sample A corn ear from your teacher (Figure 8). The kernels display
two different traits whose genes are located on different chromosomes.
2. Describe the two different traits: colour and shape. Predict which phenotypes
are dominant and which are recessive.
3. Assume that the ear of corn is from the F2 generation. The parents of the
F1 corn were pure-breeding homozygous for each of the characteristics.
Assign the letters P and p to the alleles for colour, and A and a to the alleles
for shape. Use the symbols PPaa and ppAA for the parents of the F1 generation.
Describe the phenotype of the PPaa parent and ppAA parent.
Biology 12 Lab
4. Count 100 of the kernels in sequence; describe the phenotypes and record the number
of each in a table similar to Table 1. You can rewrite the descriptions with specific
phenotypes. Once you have completed the count divide all numbers by the lowest one to
approximate the phenotypic ratio for your sample. Round the results to the nearest whole
numbers for the ratio.
Table 1
Phenotype
dominant alleles for colour and shape
dominant allele for colour, but recessive allele for shape
recessive allele for colour, but dominant allele for shape
recessive alleles for colour and shape
Number
Ratio
5. Obtain sample B. Assume that this ear was produced from a test cross using corn with
the same dominant and recessive traits. Count 100 kernels in sequence and record your
results as in step 4.
Analysis and Evaluation:
(a) What are the expected genotypes and phenotypes of the F1 generation resulting from
a cross between the parents PPaa and ppAA?
(b) Use a Punnett square to show the expected genotypes of the F2 generation for sample
A. What is the expected phenotypic ratio? Compare your results with what your results,
obtained in step 4. What factors might account for discrepancies between the
experimental and the expected results? Would your results be any different if you took
larger samples or took multiple samples and averaged the results?
(c) Assuming that sample B was produced from a test cross (i.e., B is from the
F1 generation), what is the phenotypic ratio of the F1 generation? (Use your results)
(d) What is the genotype and phenotype of the unknown parent?
(e) A dihybrid cross can produce 16 different combinations of alleles. Explain why 100
seeds were counted rather than 16.
Conclusion: Comment on how closely your results for samples A and B matched the ratios
that we predict using a punnett square. What aspects of the experiment might have
affected the results?
Lab adapted from:
Copyright © 2002 Nelson Thomson Learning
Unit 2 Lab and Study Masters 2-19