Genetic inheritance


  • Students should be able to explain the terms: • gamete

• chromosome

• gene

• allele

• dominant

• recessive

• homozygous • heterozygous • genotype

• phenotype.

Some characteristics are controlled by a single gene, such as: fur colour in mice; and red-green colour blindness in humans. Each gene may have different forms called alleles.

The alleles present, or genotype, operate at a molecular level to develop characteristics that can be expressed as a phenotype.

A dominant allele is always expressed, even if only one copy is present. A recessive allele is only expressed if two copies are present (therefore no dominant allele present).

If the two alleles present are the same the organism is homozygous for that trait, but if the alleles are different they are heterozygous.

Most characteristics are a result of multiple genes interacting, rather than a single gene.

Students should be able to understand the concept of probability

in predicting the results of a single gene cross, but recall that most phenotype features are the result of multiple genes rather than single gene inheritance.

Students should be able to use direct proportion and simple ratios to express the outcome of a genetic cross.

Students should be able to complete a Punnett square diagram and extract and interpret information from genetic crosses and family trees.

(HT only) Students should be able to construct a genetic cross by Punnett square diagram and use it to make predictions using the theory of probability.

Recognise/draw/interpret diagrams. Translate from data to a representation with a model. Use models in explanations, or match features of a model to the data from experiments or observations that the model describes or explains. Make predictions or calculate quantities based on the model or show its limitations. Give examples of ways in which a model can be tested by observation or experiment.

Understand simple probability,

Use ratios, fractions and percentages,

Understand and use the symbols: =, <, <<, >>, >, ∝, ~,

Construct and interpret frequency tables and diagrams, bar charts and histograms,

Translate information between graphical and numeric form