A genetic variant in a gene creates an allele (a different version of the gene), which produces a different phenotype.

One or both dominant alleles in the genotype for the characteristic to be expressed in the phenotype.

Two recessive alleles in the genotype for the characteristic to be expressed in the phenotype.

The combination of alleles an organism has for a characteristic (i.e. phenotype).

Features that result, at least partly, from the genetic code of an organism’s genes.

Alleles, genotype, and phenotype

Biology

Models of single-gene inheritance: Punnett squares

Models of single-gene inheritance: family tree diagrams

Explaining inheritance: Mendel and beyond

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

Gametes contain one copy of each chromosome.

Gametes contain two copies of each chromosome.

Gametes have four copies of each chromosome.

Adult body cells contain two copies of each chromosome. Gametes are sex cells. Which statement about gametes is true?

The diagram shows a chromosome pair. Four genes are shown. One gene is labelled on the left chromosome. Which position (A, B, C or D) shows the location of this gene on the right chromosome?

A plant’s flowers are either red or white. Plants with the genotypes RR and Rr have red flowers. Which allele is recessive?

A genetic variant of a gene coding for a different phenotype.

Only one copy of this type of allele will cause a phenotypic feature.

The combination of alleles an organism has for a feature.

Observable features that are at least partly caused by genes.

Two copies of this allele are needed to cause a phenotypic feature.

True or false? Different alleles have different genetic codes, so they produce a different amino acid sequence and so a protein with a different 3D shape.

Phenotype refers to an organism’s observable characteristics. Which factors can affect an organism’s phenotype?

Starting with the smallest, put these in size order.

What is the genome in a unicellular organism?

A polymer made of two nucleotide chains forming a double helix.

A monomer made of one nucleotide chain forming a helix.

A polymer made of one nucleotide chain forming a helix.

A monomer made of two nucleotide chains forming a double helix.

A polymer made of three nucleotide chains forming a triple helix.

Which is the best description of a DNA molecule?

True or false? All genes code for enzymes.

Amino acids are joined together in sequence to make a polypetide chain.

The enzyme speeds up a chemical reaction.

Put these in order to describe the production of a red pigment in a petal.

Starter Quiz

Phenotype refers to an organism’s observable characteristics. Which factors can affect an organism’s phenotype?