Inheritance, Variation and Evolution Mind Map (GCSE)

A polymer made of two strands twisted into a double helix. DNA is found in structures called chromosomes.

A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids, to make a specific protein.

The entire genetic material of an organism. The whole human genome has been studied, which helps identify genes linked to diseases and trace human migration.

Human body cells have 23 pairs of chromosomes. One pair are the sex chromosomes: XX in females and XY in males.

Male and female gametes (sperm and egg cells, or pollen and egg cells) join at fertilisation. The offspring get a mix of genes from both parents, so they vary.

One parent, no joining of gametes, and offspring that are genetically identical clones. It happens by mitosis.

Cell division that makes gametes. The chromosomes are copied, then the cell divides twice, giving four gametes, each with a single set of chromosomes and each genetically different.

The gametes join, restoring the full number of chromosomes. The new cell divides by mitosis as the embryo develops.

• Allele: a version of a gene
• Dominant: always expressed, even with only one copy
• Recessive: expressed only with two copies
• Homozygous: two identical alleles; heterozygous: two different alleles
• Genotype: the alleles present; phenotype: the characteristic shown

Show the possible offspring of two parents. Write each parent's alleles along the edges, fill in the grid, and give the outcome as a ratio, a probability or a percentage.

Crossing XX with XY gives a 50% chance of a boy and a 50% chance of a girl.

Polydactyly (extra fingers or toes) is caused by a dominant allele. Cystic fibrosis, a disorder of cell membranes, is caused by a recessive allele. Embryo screening raises ethical and economic issues.

Variation comes from the genes inherited, from the environment, or from a combination of both.

Changes to DNA happen all the time. Most have no effect, a few change the phenotype, and very rarely one gives an advantage.

Darwin's theory:

• Individuals vary because of their genes
• Those best suited to the environment are more likely to survive and breed
• They pass on the useful alleles
• Over many generations, the species changes

All species of living things evolved from simple life forms that first developed more than three billion years ago.

Choose parents with the characteristic you want, breed them, then select the best offspring and repeat over many generations. Used for disease resistance, bigger yields, gentle dogs and large flowers.

Inbreeding reduces variation, so some breeds are more prone to disease or inherited defects.

A gene from one organism is cut out and inserted into another. Examples include bacteria making human insulin, and crops resistant to insects or herbicides, or with bigger fruit.

Possible effects on wild plants and insects, and uncertain long-term effects of eating GM crops.

The remains of organisms from millions of years ago, preserved where parts did not decay, where parts were replaced by minerals, or as traces such as footprints. The fossil record is incomplete because many early forms were soft-bodied.

Bacteria reproduce quickly, so resistant strains evolve in a short time: evidence of natural selection happening now.

Edexcel only. Fossils such as Ardi and Lucy, the work of Richard Leakey's team, and the development of stone tools show how humans evolved.

Linnaeus grouped organisms into kingdom, phylum, class, order, family, genus and species, and named each with two words (genus and species). Carl Woese's three-domain system splits life into archaea, bacteria and eukaryota.