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Lesson · Grade 10 · Science

Mendel's peas: dominant and recessive alleles

  • Grade 10
  • Science
  • 1 min 50 s
  • British Columbia
  • BC10-SC-05

One diagram builds up step by step. It starts with a purple PP plant and a white pp plant, introducing allele, dominant, recessive, genotype, phenotype and homozygous along the way, and their cross gives offspring that are all Pp, heterozygous and purple. A Punnett square then crosses two of those offspring to give 1 PP, 2 Pp and 1 pp, about 3 purple to 1 white (Mendel counted 705 purple and 224 white), and the video points out that dominant does not mean more common before ending on a one-line recap.

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In one sentence

The question this lesson answers

In 1866, Gregor Mendel published his work on pea plants. How is flower colour passed on?

Each plant has two alleles for flower colour, one from each parent. An allele is a version of a gene.

Transcript

What the lesson says

In 1866, Gregor Mendel published his work on pea plants. How is flower colour passed on?

Each plant has two alleles for flower colour, one from each parent. An allele is a version of a gene.

Purple, capital P, is dominant: one copy is enough to make purple flowers.

White, small p, is recessive: it needs two copies to show.

The pair of alleles is the plant's genotype.

The feature you can see, its flower colour, is its phenotype.

Two matching alleles make a plant homozygous.

Mendel crossed these plants. Each parent passes on one allele.

Every offspring gets one of each, so it is heterozygous.

Purple is dominant, so all the offspring are purple.

The white allele is still there, hidden, not lost.

Next, Mendel crossed these offspring with each other.

A Punnett square shows how they combine. Each parent passes on a capital P or a small p, equally often.

That gives one homozygous dominant, two heterozygous, and one homozygous recessive.

Three in four have a capital P, so we expect about three purple to one white.

Mendel counted 705 purple and 224 white plants, close to three to one.

Careful: dominant does not mean more common. It means one copy is enough to show.

So one dominant allele is enough to show, and two heterozygous parents give about three purple to one white.

Curriculum

Where this fits

British Columbia, Grade 10

Science 10, Biology: patterns of inheritanceBC10-SC-05

Previous: Genes and Environment: Traits Come from BothNext: Punnett Squares: Predicting Offspring

The outcomes and strands follow the British Columbia curriculum.

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