A model used to show the inheritance of alleles from parents to offspring.

A sex cell (i.e. sperm and egg) that carries half the genetic information required for an individual organism.

The combination of alleles that an individual has for each gene.

Shows hows how much of one value there is compared to another.

A measure of the chance or likelihood of an event occurring.

Models of single-gene inheritance: Punnett squares

Biology

Alleles, genotype, and phenotype

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

a measure of the chance of an event happening

shows how much of one value there is compared to another

The nucleus of a chimpanzee body cell contains 48 chromosomes. How many chromosomes will there be in the nucleus of a chimpanzee zygote?

A woman is heterozygous (Ff) for the gene that codes for a protein. What genotypes can her eggs have?

Two heterozygous (Rr) red flowered plants cross pollinate each other. Use the Punnett square to work out the ratio of red : white flowering offspring.

A couple who are both heterozygous (Ff) for the A gene want to have a child. Use the incomplete Punnett square to work out the probability that the child will be homozygous recessive.

Flowers can be red (RR or Rr) or white (rr). A single plant with red flowers pollinates itself. Some of the offspring plants have white flowers. What was the genotype of the parent plant?

The sequence of amino acids in a protein.

The sequence of nucleotides bases in protein.

Genotype at least partly depends on phenotype.

Phenotype at least partly depends on genotype.

Which statement best describes the relationship between phenotype and genotype?

Horse body cells have 64 chromosomes. How many chromosomes will there be in a horse's unfertilised egg cell?

True or false? Offspring inherit different genes from each parent.

In humans the CF protein affects the stickiness of mucus. There are two alleles F and f. Individuals with the genotype ff have very sticky mucus. Which allele is dominant?

The petal cells contain a colourless chemical.

The enzyme catalyses a chemical reaction.

The colourless chemical is converted to a red pigment.

Plants produce either red pigmented flowers or white flowers with no pigment. The RR or Rr genotypes have red flowers. Plants with rr genotype have white flowers. Order the statements to explain how.

Starter Quiz

Which is the genetic code?