Paleobio Home Cassit Birds: Lessons on Genes, Inheritance,and Evolution
Lesson One

Written by Jennifer A. Collins
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Concept: Features are passed from parents to offspring. These features of an individual (phenotype) are determined by its genes (genotype) which are found in the chromosomes of its DNA.

Overview: Students study a family of Cassit birds and recognize distinguishing features that have been inherited. They then learn that these features (phenotypes) are coded for in the DNA of the birds as genes on chromosomes.

Time: 30-40 minutes

Vocabulary: phenotype, genotype, homozygous, heterozygous, allele

Advance Preparation: Make overheads


  • Cassit Bird Family
  • Cassit Bird Cells

    Procedure: 1. Show students an overhead/picture of a Cassit Bird Family. Keep the phenotype information covered. Explain to students that these are Cassit birds (made-up for purposes of simplicity). Ask students to identify some of the distinguishing phenotypes (features) of the birds. Write these on the board. Explain that what they listed are phenotypes and are the result of gene expression (H.S. You can discuss that not all features are determined by genes). Uncover the phenotype information. Explain that students will concentrate on the following phenotypes: beak shape, chest patches, and sex.

    2. Ask students to identify similarities and differences between the parents and offspring and between offspring. Ask students how this happens. Students brainstorm responses, which should lead to a discussion of inheritance.

    3. Show students the Cassit Bird Cells as an overhead. Explain that this is a representative cell taken from a Cassit bird. It shows the genetic material/chromosomes in each cell, which is the basis for the features expressed in the birds. Ask students the following questions. These may be a review of previous concepts covered in class:

  • What is a chromosome? (Organized genetic material that is made up of DNA) Where do you find them? (Inside the nucleus)
  • How many chromosomes do Cassit Birds have? (5 pairs, 10 individual)
  • Why does one pair of chromosomes not look like the others? (They are the sex chromosomes and since this is a male, it has two X chromosome. Unlike humans, it is the female with XY and male with XX).
  • What is a gene? (A section of DNA that codes for a protein.) Where are the genes located? (They make up chromosomes, they can be identified on these drawings as lines on the chromosomes.

    4. Show students the gene locations for the features that they will be keeping track of (beak shape, chest patches, sex). Explain that the genes for two of these features are found on the same chromosome (#1). The combination of the genes determine the phenotype of that offspring. Discuss homozygous, heterozygous.

    5. Have students work in pairs to determine the genotype and phenotype of the different birds in the family, then share their responses with the rest of the class.

  • ©   Updated: June 2003   Contact: jen-AT-paleobio or allen-AT-paleobio