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Step 3b: Inheritance

How is the disorder-causing allele inherited?

What is a Inheritance

This introductory video provides a very general overview of asexual and sexual reproduction and how sexual reproduction contributes to genetic variation.

Project video to the whole class.

  • During reproduction, genetic information [DNA] passes from parent to offspring.
  • During sexual reproduction, individuals inherit two copies of each gene, one from each parent.
  • Sexual reproduction contributes to genetic variation.

5 minutes

What is Inheritance?

What Are Chromosomes?

This page introduces the structure and function of chromosomes.

Project web page to the whole class and highlight the main points.

  • Chromosomes are packages DNA.
  • Chromosomes keep DNA organized during cell division.
  • Each chromosome has many genes.

5 minutes

What Are Chromosomes?

Build a Chromosome (Optional)

Students build a paper model of a chromosome to understand its structure and its relationship to DNA and genes.

  • Chromosomes are packages of condensed DNA.
  • One chromosome contains many genes.
  • Chromosomes are made of DNA that is coiled around protein "spools" called histones.

45 minutes

Teacher Guide (pdf)

Student Instructions (pdf)
Make one copy per student or pair, or have students view online (copies may be re-used).

Cut-outs (pdf)
Make one single-sided copy per student or pair. Cut-outs may be laminated and re-used.

Allele Shuffling

This video shows how different versions of genes, called alleles are shuffled during sexual reproduction. It highlights how recombination, gamete formation (independent assortment), and random pairing of gametes each contribute to genetic and phenotypic variation.

Project video to the whole class.

  • Variations in the DNA sequences of genes are called alleles.
  • Alleles are shuffled during sexual reproduction (recombination, independent assortment, and fertilization).
  • Allele shuffling during sexual reproduction contributes to genetic variation in a population.
Cause & Effect

Students see an overview of how recombination and independent assortment (cause) contribute to genetic variation (effect).

5 minutes

Build-a-Bird

This paper model of sexual reproduction uses real pigeon traits to demonstrate how two parents can produce highly varied offspring. Students recombine parental chromosomes, make gametes, then randomly combine two gametes. Finally, they decode the resulting allele combinations to draw the traits of a pigeon offspring.

Note: For simplicity, we’ve placed alleles on one chromosome.

After students complete their pigeons, hang them (along with the gametes they used to make them) all on a large wall space or white board. Discuss the following:

  • Where the alleles came from in the first place (answer: in a previous geneation, there was a mutation in a reproductive cell)
  • How allele “shuffling” during sexual reproduction contributes to genetic and phenotypic variation in offspring
  • The amount of genetic and phenotypic variation you see in the offspring from just two pigeons

Time-saving tip: Have students work in pairs to recombine the chromosomes, then have each student choose two gametes from the same parents to build their own bird.

To find more information about pigeon traits, visit Pigeon Breeding: Genetics At Work

  • Variations in the DNA sequences of genes are called alleles.
  • Alleles are shuffled during sexual reproduction (recombination, independent assortment, and random fertilization).
  • Allele shuffling during sexual reproduction contributes to genetic variation in a population.
Developing and/or Using Models

Paper chromosomes are manipulated to model crossing over and independent assortment as generators of genetic variation.

Cause & Effect

Students visualize how crossing over and independent assortment (cause) increases genetic variation (effect).

45 minutes

Scissors, tape, colored pencils

Student Instructions (pdf)

Make one copy per student or pair (copies may be re-used), or have students view on tablets or computers.

Chromosome Cut-Outs (pdf)

Make one copy per student or pair.