Codominance & Incomplete Dominance Practice Worksheet
Table of Contents :
Codominance and incomplete dominance are important concepts in genetics that describe how alleles interact to influence the phenotype of an organism. Understanding these concepts is vital for students studying heredity and the principles of genetics. In this article, we will explore the definitions and examples of codominance and incomplete dominance, followed by practical exercises that will help reinforce these concepts.
Understanding Codominance
Codominance occurs when two alleles of a gene are expressed equally in the phenotype of the organism. This means that neither allele is dominant or recessive; instead, both contribute to the organism's characteristics. A classic example of codominance is seen in blood types.
Example of Codominance: Blood Types
In human blood types, the A and B alleles are codominant. When an individual inherits one A allele and one B allele, they will express the AB blood type. Below is a summary of the human blood groups demonstrating codominance:
<table> <tr> <th>Genotype</th> <th>Phenotype (Blood Type)</th> </tr> <tr> <td>IA IA</td> <td>A</td> </tr> <tr> <td>IB IB</td> <td>B</td> </tr> <tr> <td>IA IB</td> <td>AB</td> </tr> <tr> <td>ii</td> <td>O</td> </tr> </table>
Key Points on Codominance
- In codominance, both alleles are fully expressed, resulting in a phenotype that is a combination of both traits.
- No allele masks the expression of the other, which is different from complete dominance.
Understanding Incomplete Dominance
Incomplete dominance, on the other hand, occurs when the phenotype of a heterozygous individual is intermediate between the phenotypes of the two homozygous parents. Here, neither allele is completely dominant over the other, resulting in a blending of traits.
Example of Incomplete Dominance: Flower Color
A classic example of incomplete dominance can be observed in the snapdragon flower. When a red-flowered plant (RR) is crossed with a white-flowered plant (WW), the resulting offspring (RW) will have pink flowers.
Incomplete Dominance Table
<table> <tr> <th>Genotype</th> <th>Phenotype (Flower Color)</th> </tr> <tr> <td>RR</td> <td>Red</td> </tr> <tr> <td>WW</td> <td>White</td> </tr> <tr> <td>RW</td> <td>Pink</td> </tr> </table>
Key Points on Incomplete Dominance
- The phenotype of heterozygous individuals appears as a blend of the two homozygous traits.
- Incomplete dominance demonstrates that dominant alleles do not always overpower recessive ones in a straightforward manner.
Practice Worksheet: Codominance & Incomplete Dominance
Below is a practice worksheet designed to reinforce your understanding of codominance and incomplete dominance. Answer the following questions and scenarios based on the information provided above.
Section A: Codominance
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If a person with genotype IAIB (AB blood type) has a child with a person with genotype ii (O blood type), what are the possible blood types of their child?
- A: ____________
- B: ____________
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In cattle, the allele for red coat color (R) is codominant with the allele for white coat color (W). What coat colors would you expect from the following crosses?
- a. RR x WW: ______________
- b. RW x RW: ______________
Section B: Incomplete Dominance
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If a blue flowered plant (BB) is crossed with a white flowered plant (WW) and the offspring are all blue-white flowers (BW), what color would you expect if you crossed two of these BW plants?
- A: ____________
- B: ____________
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In a species of fish, the allele for yellow color (Y) shows incomplete dominance over the allele for blue color (B). What color would you expect from a cross between a yellow fish (YY) and a blue fish (BB)?
- A: ______________
Important Notes
"Completing this worksheet is essential to solidify your understanding of how codominance and incomplete dominance work, as well as their implications in genetic inheritance."
By engaging with these concepts and exercises, students can gain a deeper insight into how genetic traits are expressed and inherited. Understanding codominance and incomplete dominance is not only pivotal for academic success in biology but also provides a foundational knowledge for exploring more complex genetic concepts in the future. 🌱🧬