Genetics

An allele is any of the alternative forms of a gene or DNA sequence that can occupy the same position, or locus, on a chromosome.

A chromosome is a thread-like structure of DNA and protein that carries an organism's genes; most human cells hold 46 of them in 23 pairs.

Codominance is a pattern of inheritance in which both alleles in a heterozygote are fully expressed, so the traits of both appear together.

Crossing over is the exchange of matching DNA segments between paired homologous chromosomes during meiosis, creating new combinations of alleles.

Diploid describes a cell or organism with two complete sets of chromosomes, one inherited from each parent, as in most human body cells.

A dominant allele is a version of a gene whose effect shows in the phenotype even when only one copy is present, masking a recessive allele.

The structure of DNA: nucleotides, the sugar-phosphate backbone, base pairs and hydrogen bonds, antiparallel strands and the grooves.

The stages of mitosis, from prophase to telophase and cytokinesis: how one cell's copied chromosomes are shared equally between two new cells.

How a cell makes a protein: a gene is transcribed into mRNA in the nucleus, processed and exported, then translated by a ribosome.

How a replication fork copies DNA: helicase opens the helix, primase lays primers, and DNA polymerase builds a leading and a lagging strand.

How PCR copies one stretch of DNA: heat the strands apart, cool so primers bind, let Taq build new strands, and repeat until the copies number billions.

Two strands of DNA wound round each other, held together by base pairs: twelve of them here, about one full turn of the double helix.

The adaptor of protein synthesis: an L-shaped RNA of 76 nucleotides that reads a codon at one end and carries an amino acid at the other.

The first step in packing DNA into chromosomes: 147 base pairs of DNA wrapped almost twice round a core of eight histone proteins.

Studies the breeding, nutrition, growth and health of farm animals to improve their welfare and the food they produce.

Analyses evidence from crimes, such as blood, DNA, fibres and drugs, and reports what it shows to investigators and the courts.

Helps people and families understand inherited conditions and genetic test results, and what those mean for their health and choices.

Studies how genes are passed on and how changes in DNA shape traits and disease, in people, animals, plants or microbes.

Studies how plants grow, fight off disease and respond to soil and climate, and uses that knowledge to improve crops.

Uses programming and statistics to make sense of biological data, from DNA sequences and gene expression to protein structures.

The reverse complement, complement or reverse of a DNA or RNA sequence, or DNA written as RNA, from bare letters or FASTA.

Every open reading frame in all six frames, with its position, length and protein, from ATG or any start codon.

GC content, base counts, length and molecular weight of a DNA or RNA sequence, with GC along the sequence in a sliding window.