Mendel investigated the inheritance of traits (e.g. flower colour and seed texture) in pea plants in the 1850s-60s.
Earlier scientists thought traits blended during sexual reproduction; Mendel showed traits were dominant and recessive.
Mendel suggested heritable ‘factors’ caused traits; other scientists discovered DNA in 1869 and genes in the 1900s.
Theories about heredity developed over time; 1943: DNA associated with inheritance; 1953: structure of DNA worked out.
Over recent decades scientists have discovered the importance of studying whole genomes, not just individual genes.

Common misconception

Two genes are inherited, both alleles contribute to the genotype; scientists work in isolation from one another.

Keep repeating that alleles are different codes for the same protein, different proteins lead to different traits (phenotypes). Scientists build on the work of others, and critique each other's work, to build a better understanding.

Keywords

Heredity - the process of passing traits from parents to their offspring through reproduction
Trait - a specific characteristic that is part of an organism’s phenotype
Recessive - two alleles must be present in the genotype for the characteristic to be expressed in the phenotype
Dominant - one or two alleles must be present in the genotype for the characteristic to be expressed in the phenotype
DNA - a chemical molecule made of nucleotides, which contains the genetic code for making proteins in all living organisms

With the history, the dates aren't important, focus on the flow of ideas, one building on another through time.

Teacher tip

Equipment

None required.

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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6 Questions

Q1.

One gene controls pea pod shape. The inflated pod allele (I) is dominant. The constricted pod allele (i) is recessive. How many i alleles must a pea plant inherit to have constricted pods?

1 or 2

Correct answer: 2

Q2.

The diagram is a model of the inheritance of I and i alleles from two parent pea plants. What is this type of diagram called?

evolutionary tree

family tree

food web

Correct answer: Punnett square

Q3.

Two pea plants with the genotype Ii are bred together. Which Punnett square has been completed correctly to show the possible genotypes of the offspring plants?

Correct answer: C

Q4.

The Punnett square shows that the proportion of offspring that will have the genotype ii is in 4.

Correct Answer: 1, one

Q5.

What is the probability that an offspring of these parent plants will have the genotype ii?

Correct Answer: 0.25, 25%, 25 %, 1 in 4

Q6.

The allele for inflated pods (I) is dominant. The Punnett square shows that the ratio of individuals with inflated pods to constricted pods in the offspring will be :1.

Correct Answer: 3, three

Exit quiz

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6 Questions

Q1.

Who investigated the inheritance of traits in pea plants in the 1850s and 1860s?

Francis Crick

Correct answer: Gregor Mendel

Marie Maynard Daly

Rosalind Franklin

Q2.

True or false? Mendel suggested that the traits he investigated were linked to heritable alleles.

true

Correct answer: false

Q3.

Mendel investigated inheritance of flower colour. The allele for purple flowers is dominant (P), and for white flowers is recessive (p). What colour flowers will a Pp plant have?

a blend of purple and white

Correct answer: purple

white

Q4.

Mendel bred two pea plants, as shown in the Punnett square. He called the offspring the F1 generation. How many of the F1 generation plants are likely to have white flowers?

Correct Answer: 0, none, zero

Q5.

Mendel bred two of the F1 generation plants, as shown in the Punnett square. He called the offspring the F2 generation. He showed that the ratio of purple to white flowered F2 plants was :1.

Correct Answer: 3, three

Q6.

Starting with the earliest, put the scientific discoveries in order.

1 - Pea plant traits were linked to dominant and recessive heritable “factors”.

2 - An X-ray image of DNA was produced.

3 - The 3D structure of the DNA double helix was worked out.

4 - The gene and alleles linked to smooth and wrinkled peas were identified.

5 - The human genome was sequenced.