3b - Variation and Mutation

Alleles

等位基因 (děngwèi jīyīn) Different forms or versions of the same gene, found at the same locus on homologous chromosomes. They are a primary source of genetic variation.

Continuous variation

连续变异 (liánxù biànyì) Variation in a characteristic where individuals show a range of phenotypes with smooth gradations between extremes (e.g., height, weight). Often influenced by multiple genes (polygenic) and the environment.

Deletion

（基因）缺失 ((jīyīn) quēshī) A type of gene mutation where one or more nucleotide bases are removed from the DNA sequence, often causing a frameshift and significantly altering the resulting protein.

Discontinuous variation

不连续变异 (bùliánxù biànyì) Variation in a characteristic where individuals fall into distinct, clear-cut categories with no intermediates (e.g., blood groups, tongue rolling). Often controlled by a single gene or a few genes.

Environmental variation

环境变异 (huánjìng biànyì) Differences between individuals that are due to environmental factors (e.g., diet, climate, lifestyle) rather than inherited genetic differences.

Genetic variation

遗传变异 (yíchuán biànyì) Differences between individuals that are due to variations in their genes or DNA sequences, inherited from their parents. The raw material for evolution.

Mutagen

诱变剂 (yòubiànjì) An agent, such as radiation (e.g., UV, gamma rays) or certain chemicals (e.g., in tobacco smoke), that can cause an increase in the rate of mutation in DNA.

Mutation

突变 (tūbiàn) A random, spontaneous, and permanent change in the nucleotide sequence of an organism's DNA (gene mutation) or in the structure or number of its chromosomes (chromosome mutation). The ultimate source of new alleles.

Natural selection

自然选择 (zìrán xuǎnzé) The process by which organisms with heritable traits better suited to their environment are more likely to survive, reproduce, and pass those advantageous traits to their offspring. Acts on variation.

Phenotype

表现型 (biǎoxiànxíng) The observable characteristics of an organism, resulting from the interaction of its genotype (genes) and the environment. Variation is observed in phenotypes.

Sexual Reproduction

有性生殖 (变异来源) (yǒuxìng shēngzhí (biànyì láiyuán)) A mode of reproduction involving the fusion of gametes from two parents, leading to offspring with a unique combination of alleles from both parents, thus increasing genetic variation through meiosis and fertilization.

Substitution

（基因）替换 ((jīyīn) tìhuàn) A type of gene mutation where one nucleotide base is replaced by another. May result in a different amino acid (missense), a stop codon (nonsense), or no change (silent) due to degenerate genetic code.

Variation

变异 (biànyì) Any difference in characteristics (traits) between individuals of the same species. Can be genetic or environmental, continuous or discontinuous.