the process of passing traits from parents to their offspring through reproduction

a specific characteristic that is part of an organism’s phenotype

two alleles must be present in the genotype for the characteristic to be expressed in the phenotype

one or two alleles must be present in the genotype for the characteristic to be expressed in the phenotype

a chemical molecule made of nucleotides, which contains the genetic code for making proteins in all living organisms

Explaining inheritance: Mendel and beyond

Biology

Alleles, genotype, and phenotype

Models of single-gene inheritance: Punnett squares

Models of single-gene inheritance: family tree diagrams

The inheritance of biological sex in humans

Pupils will learn about growth through cell division, mitosis as part of the cell cycle, cancer as the result of changes in cells that lead to uncontrolled growth and division, and the formation of gametes by meiosis.

Pupils learned about what the genome is, what it’s made of and where it’s stored, more detail about the chemical structure of DNA, and the relationship between an organism’s genome and its phenotype.

This unit covers key genetic terms, single-gene inheritance, and genetic crosses, including probability and ratios. It explores how most traits result from multiple genes and sex determination in humans. The unit also includes interpreting data and using models to solve problems.

Inheritance, genotype and phenotype

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

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

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?

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?

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.

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

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

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

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

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?

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?

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?

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

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

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.

Exit Quiz

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