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Grade 10 Intermediate About 20 min Version 1 Awaiting review Premium

Inheritance: Mendel's pea crosses

Gregor Mendel studied pea plants. Height is controlled by one gene with two forms, or alleles: T for tall, which is dominant, and t for short, which is recessive. Every plant has two alleles, one from each parent. TT and Tt plants are tall, because the dominant T hides t; only tt plants are short. When a plant makes gametes (pollen or egg cells), each gamete gets just one of its two alleles. A Punnett square shows every way the gametes can combine, so you can predict the fraction of offspring with each genotype (the alleles) and phenotype (what the plant looks like).

What you will learn

  • Use a Punnett square to predict the offspring of a cross.
  • Explain dominant and recessive alleles, genotype and phenotype.
  • Explain Mendel's 3 : 1 ratio and the use of a test cross.

Before you start

  • Know that genes are carried on chromosomes and passed from parents to offspring.

Materials

  • Punnett square worksheet

Equipment

  • None for the virtual lab

Procedure

  1. Cross a pure tall plant (TT) with a short plant (tt) and record the offspring (the F1 generation).
  2. Cross two of the F1 plants (Tt × Tt) and record the expected offspring out of 4 and out of 1000.
  3. Cross a Tt plant with a short tt plant (a test cross) and record.

How this simulation is simplified

  • Each gamete gets one of the parent's two alleles with equal chance; the counts shown are the expected numbers.