Edexcel GCSE Biology: Meiosis, DNA, Genetics, and Natural Selection

Comprehensive vocabulary flashcards covering Edexcel Biology topics including meiosis, DNA structure, extraction, protein synthesis, genetic mutations, monohybrid and sex-linked inheritance, codominance, polygenic traits, and Darwinian natural selection.

Reduction division

A form of cell division (meiosis) in which the chromosome number is halved from diploid to haploid, producing four genetically different haploid daughter cells.

Gamete

A haploid sex cell containing half the normal number of chromosomes, such as sperm cells and egg cells in animals, or pollen grains and ovum cells in plants.

Recombinant chromosomes

Chromosomes created during meiosis when sections of DNA are swapped between paired maternal and paternal chromosomes along the centre of the cell.

DNA (Deoxyribonucleic acid)

The genetic material located in the nucleus of a cell, structured as a polymer made up of two antiparallel strands coiled around each other into a double helix.

Nucleotide

The repeating monomer subunit of DNA, consisting of a deoxyribose sugar, a phosphate group, and one of four nitrogenous bases attached to the sugar.

Complementary base pairing

The specific pairing of nitrogenous bases held together by weak hydrogen bonds in DNA, where Adenine always pairs with Thymine (A-T) and Cytosine always pairs with Guanine (C-G).

Detergent (DNA extraction)

A chemical solution (such as washing-up liquid) used during DNA extraction to break down cell membranes and nuclear membranes, releasing DNA from the fruit cells.

Ice-cold ethanol (DNA extraction)

Cold alcohol added slowly down the side of a test tube to cause DNA to precipitate out of the filtrate as a stringy white solid, because DNA is insoluble in cold alcohol.

Gene

A section of DNA with a particular sequence of bases that codes for a specific sequence of amino acids in a polypeptide chain.

Transcription

The first stage of protein synthesis occurring in the nucleus, where RNA polymerase unwinds the DNA and synthesizes a complementary single-stranded mRNA molecule from a gene.

RNA polymerase

The enzyme that binds to a non-coding region of DNA just in front of a gene and synthesizes a complementary mRNA transcript.

Uracil

The nitrogenous base present in RNA nucleotides that replaces thymine (T) and pairs with adenine (A).

Translation

The second stage of protein synthesis occurring in the cytoplasm, in which a ribosome reads mRNA codons to assemble amino acids in a specific order into a protein.

Codon

A triplet of bases on an mRNA molecule that codes for one specific amino acid.

tRNA (Transfer RNA)

A type of RNA molecule in the cytoplasm featuring an anticodon at one end and a specific amino acid binding site at the other; at least $20$ different types exist to transfer amino acids to ribosomes.

Anticodon

A triplet of unpaired bases on a tRNA molecule that pairs with a complementary codon on an mRNA strand.

Genetic variants in non-coding DNA

Mutations occurring in regions where RNA polymerase binds; they affect phenotype by making binding easier or more difficult, altering the quantity of mRNA transcribed and protein produced.

XDH enzyme variant

A mutated enzyme variant in fruit flies caused by an alteration in coding DNA, leading to decreased enzyme activity and resulting in brown eyes instead of normal red eyes.

Monohybrid inheritance

The pattern of inheritance for characteristics that are controlled by a single gene.

Pure breeding

A term describing an individual that is homozygous for a particular characteristic, possessing two identical alleles (e.g. $TT$ or $tt$).

F2 generation phenotypic ratio

The characteristic $3:1$ phenotypic ratio ($75\%$ dominant to $25\%$ recessive) obtained when offspring from the pure-breeding parental cross ($Tt$) interbreed.

Family pedigree diagram

A chart used to trace the pattern of inheritance of a characteristic or genetic disease across generations, using squares to represent males and circles to represent females.

Sex chromosomes

The pair of chromosomes responsible for determining biological sex, where human females carry $XX$ and human males carry $XY$.

Codominance

An inheritance pattern in which both alleles within a genotype are expressed in the individual's phenotype, such as alleles $I^A$ and $I^B$ producing the $AB$ blood group.

Sex-linked characteristic

A trait governed by alleles located on the sex chromosomes (almost always the $X$ chromosome), making recessive conditions like haemophilia and red-green colour blindness far more prevalent in males.

Carrier

A female with one normal dominant allele masking one recessive disease allele on her $X$ chromosomes; she shows no symptoms but has a $50\%$ chance of passing the condition to offspring.

Polygenic inheritance

The inheritance of traits controlled by multiple genes interacting with each other, producing a wide spectrum of phenotypic variations such as eye colour.

Continuous variation

Phenotypic variation that results from a combination of genetic potential and external environmental factors, such as human height.

Discontinuous variation

Variation that is controlled exclusively by genetic factors and falls into discrete categories, such as ABO blood groups or free versus fixed earlobes.

Insertion mutation

A mutation where an extra base is randomly added into the DNA sequence, changing that triplet and shifting every subsequent triplet further along the sequence.

Substitution mutation

A mutation where a base in the DNA sequence is randomly swapped for another base, altering only the single amino acid coded by that triplet without causing a knock-on frameshift.

Sickle cell anaemia

The first described genetic disease caused by a gene mutation that alters haemoglobin, making red blood cells stiff and sickle-shaped, which obstructs narrow blood vessels.

Mutagenic agents

Environmental factors that increase the frequency of DNA mutations, including ionizing radiation (gamma rays, X-rays, ultraviolet rays) and chemicals such as tar in tobacco.

Evolution

The change in the frequency of a phenotype in a population over many generations.

Natural selection

Charles Darwin's mechanism of evolution stating that individuals with traits best suited to their environment survive longer, reproduce more successfully, and pass those beneficial alleles to the next generation.

Peppered moth (Biston betularia)

An observed example of natural selection where industrial pollution darkened tree bark, providing a camouflage survival advantage to dark moths and increasing the frequency of the dark phenotype.