Decoding Dominance: Exploring Co-dominance and Incomplete Dominance

Biology Grades High School 3:28 Video
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Lesson Description

This lesson explores the concepts of co-dominance and incomplete dominance in genetics, contrasting them with complete dominance. Students will learn how different allele interactions affect phenotype expression, using examples like blood type and flower color.

Video Resource

Co-dominance and Incomplete Dominance | Biomolecules | MCAT | Khan Academy

khanacademymedicine

Duration: 3:28
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Key Concepts

  • Complete Dominance
  • Co-dominance
  • Incomplete Dominance
  • Genotype vs. Phenotype
  • Alleles (Homozygous and Heterozygous)

Learning Objectives

  • Differentiate between complete dominance, co-dominance, and incomplete dominance.
  • Predict the phenotype resulting from different genotypes under various dominance patterns.
  • Explain how co-dominance and incomplete dominance contribute to phenotypic variation.

Educator Instructions

  • Introduction (5 mins)
    Begin by reviewing basic genetics concepts like alleles, homozygous, heterozygous, genotype, and phenotype. Briefly discuss complete dominance as a foundation. Show the Khan Academy video: Co-dominance and Incomplete Dominance | Biomolecules | MCAT | Khan Academy.
  • Video Analysis and Note-Taking (15 mins)
    Students watch the video and take notes on the key differences between complete dominance, co-dominance, and incomplete dominance. Encourage them to focus on the flower color examples provided in the video.
  • Concept Clarification (10 mins)
    Facilitate a class discussion to clarify any confusion regarding the three dominance patterns. Use the blood type (A, B, O) and flower color examples from the video and transcript to reinforce understanding.
  • Application and Problem Solving (15 mins)
    Present example scenarios involving different traits and inheritance patterns (complete, co-, and incomplete dominance). Have students predict the phenotypes based on given genotypes. Examples could include feather color in chickens (co-dominance) or snapdragon flower color (incomplete dominance).
  • Wrap-up and Assessment (5 mins)
    Administer a short multiple-choice and fill in the blank quiz to assess understanding of the key concepts. Review answers and address any remaining questions.

Interactive Exercises

  • Dominance Pattern Scenarios
    Provide students with a series of genotype/phenotype scenarios and ask them to identify the dominance pattern (complete, co-, or incomplete) that best explains the observed inheritance.

Discussion Questions

  • How does co-dominance differ from incomplete dominance in terms of phenotype expression?
  • Can you think of examples of co-dominance or incomplete dominance in humans (besides blood type)?
  • Why is understanding different dominance patterns important for predicting inheritance patterns?

Skills Developed

  • Critical Thinking
  • Problem Solving
  • Data Interpretation
  • Scientific Reasoning

Multiple Choice Questions

Question 1:

In complete dominance, which allele is expressed in the phenotype when a heterozygous genotype is present?

Correct Answer: Only the dominant allele

Question 2:

What happens to the alleles in co-dominance?

Correct Answer: Both alleles are fully expressed simultaneously

Question 3:

In incomplete dominance, a heterozygous genotype results in:

Correct Answer: A blended phenotype

Question 4:

If a red flower (RR) is crossed with a white flower (WW) and the offspring are all pink (RW), this is an example of:

Correct Answer: Incomplete dominance

Question 5:

Blood type AB is an example of:

Correct Answer: Co-dominance

Question 6:

Which of the following is NOT a pattern of inheritance discussed in the video?

Correct Answer: Polygenic inheritance

Question 7:

What is the genotypic ratio of the offspring if you cross two heterozygous individuals showing incomplete dominance?

Correct Answer: 1:2:1

Question 8:

A plant with the genotype CRCW produces flowers with both red and white patches. This is most likely an example of:

Correct Answer: Co-dominance

Question 9:

If allele A is dominant over allele a, what is the phenotype of an individual with genotype Aa?

Correct Answer: Dominant

Question 10:

If a black chicken (BB) is crossed with a white chicken (WW) and all the offspring are black and white speckled (BW), this is an example of:

Correct Answer: Co-dominance

Fill in the Blank Questions

Question 1:

An individual with two identical alleles for a trait is called ________.

Correct Answer: homozygous

Question 2:

The physical expression of a gene is known as the ________.

Correct Answer: phenotype

Question 3:

In ________ dominance, the heterozygous phenotype is a blend of the two homozygous phenotypes.

Correct Answer: incomplete

Question 4:

________ dominance occurs when both alleles are fully expressed in the heterozygous phenotype.

Correct Answer: Co-

Question 5:

A person with blood type O has the genotype ________.

Correct Answer: OO

Question 6:

The genetic makeup of an organism is called its ________.

Correct Answer: genotype

Question 7:

Alleles are different forms of a ________.

Correct Answer: gene

Question 8:

In complete dominance, the ________ allele masks the expression of the recessive allele in a heterozygote.

Correct Answer: dominant

Question 9:

Snapdragon flower color is an example of ________ dominance.

Correct Answer: incomplete

Question 10:

The ABO blood group system is an example of both complete dominance and ________.

Correct Answer: co-dominance

Educational Standards

B.LS3.1:Ask questions to clarify relationships about the role of DNA and chromosomes in coding the instructions for characteristic traits passed from parents to offspring. B.LS3.3:Apply concepts of statistics and probability to explain the variation and distribution of expressed traits in a population.

Teaching Materials

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