How is inheritance explained?

Build a Bird

INTRODUCTION

We inherit one copy of each gene from each of our parents. Variants of these genes are known as alleles. Each individual possesses two alleles for each gene. These alleles can be represented by a genotype, which encodes for our phenotype. When studying genetics and inheritance, monohybrid and dihybrid crosses are effective ways to track the possible phenotypes inherited from two parents to their offspring for one or two traits respectively. In this investigation, you are going to flip coins to build a bird then breed it with one of your classmate’s birds and predict the potential genotypes of your offspring.

AIM

To simulate inheritance patterns of genes across generations.

Method

Part A: Determine the characteristics of your bird

1. To determine the genotype of your bird’s eye colour, flip the two coins at once. Heads represent the dominant allele (E), whilst tails represents the recessive allele (e). This means that if you flip one head and one tail, your bird would be heterozygous and have the genotype Ee, which codes for blue eyes.

2. Write your bird’s genotype for eye colour in Table 1, then use Figure 1 to determine the phenotype.

3. Repeat steps 1 and 2 for wing colour, body colour, and beak length. Be sure to notice that some phenotypes are incompletely dominant.

4. Using the data collected in Table 1, colour in the eyes, wings, and body of your bird in Figure 2. Also draw on the beak.

5. Flip one coin to determine the sex of your bird. Heads means it is male, tails means it is female. Circle the result on the top left of your bird picture.

6. Pair up with a classmate that has created a bird of the opposite sex.

Part B: Determine your offspring’s eye colour

7. Eye colour is found on an autosome and is unlinked to any of the other traits. Complete the Punnett square in Figure 3, then complete the sentence explaining the phenotypic percentage frequency.

8. Using the code in the top left corner of each box in the Punnett square, flip one coin twice. Note your two results down – H means heads, and T means tails. The order in which you flipped the coins is reflected in Figure 3 – for example, if you flipped a heads and then a tails, then your offspring will have the genotype shown in the top-right box. Once it is determined, complete Table 2 and colour in the eye of your offspring bird in Figure 6.

Part C: Determine your offspring’s wing and body colour

9. Wing and body colour genes are found on different autosomes. These genes assort independently. Complete the dihybrid cross in Figure 4, then complete the sentence explaining the phenotypic percentage frequency.

10. Again, using the code in the top left corner of each box in the Punnett square, flip one coin four times. Once the offspring’s wing and body colours are determined, complete Table 3 and colour in the wing and body of your bird in Figure 6.

Part D: Determine your offspring’s beak length

11. Beak length genes are found on the X-chromosome of the bird. Complete the monohybrid cross in Figure 5, then complete the sentence explaining the phenotypic percentage frequency.

12. Using the code in the top left corner of each box in the Punnett square, flip one coin two times. Once the offspring’s beak length is determined, complete Table 4 and draw the beak on your bird in Figure 6.

DISCUSSION QUESTIONS

1. What is meant by the term ‘phenotype’?

2. Distinguish between incomplete dominance and codominance and identify which is relevant to the bird’s eye colour.

3. In the class, which traits appeared most frequently and why?

4. If a pedigree chart were to be made for short beak length, explain some of the characteristics that would be seen on the chart.

5. What would happen to the frequency of recessive phenotypes if another generation of offspring were produced?

6. Explain whether your phenotypic ratios would be the same if offspring wing and body colour were linked genes.

7. Explain why a simulation is useful for an inheritance-based investigation.

8. Imagine all individuals with short beaks died due to an environmental selection pressure. Explain what would happen to the gene pool for beak size.

CONCLUSION

Write a concluding paragraph to summarise your investigation. Be sure to include:

• whether the aim was achieved by referring to your results and your class results

• limitations in the simulation

• potential ways to improve the simulation

• broader implications of your research or further areas of exploration that stem from your findings.