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Science

Genetic variation and genetic disorders

Genetic diagrams

Gregor Mendel (1822-1884) studied the inheritance of different characteristics in pea plants. He found that when he bred red-flowered plants with white-flowered plants, all the offspring produced red flowers. If he bred these plants with each other, most of the offspring had red flowers, but some had white. This was because the allele for red flowers is dominant, and the allele for white flowers is recessive. Genetic diagrams help to show how this works.

In a genetic diagram, you show all of the possible alleles for a particular characteristic. There will be two alleles from one parent, and two from the other parent, making four altogether. You then draw lines to show all the possible ways that these alleles could be paired in the offspring. There will be four possible ways, but some or all of them could be repeated.

Genetic diagram of FF x ff for flower colours

A genetic diagram showing the outcome of Mendel's first cross. All the offspring have red flowers, even though they carry the recessive allele for white flowers

In genetic diagrams, the dominant allele is shown as a capital letter, while the recessive allele is shown as a lower-case letter.

Genetic diagram of Ff x Ff for flower colours

A genetic diagram showing the outcome of Mendel's second cross. Three-quarters of the offspring have red flowers and a quarter have white flowers

Back to Cell division and inheritance index

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