Mendelism and evolution / by E.B. Ford.

  • Ford, E. B. (Edmund Briscoe), 1901-1988.
Date:
1931
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Mendelism and evolution / by E.B. Ford. Source: Wellcome Collection.

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    110 MENDELIláM AND EVOLUTION F2. The second filial generation ; the grandchildren of a given mating. Factor. See ' Gene Factor-pair. See ' Gene Gamete. A reproductive cell of either sex ; a sperm or an ovmn in higher animals, a pollen grain or an ovule in higher plants. Gastrula. A stage in the development of multi-cellular animals when the embryo consists of a two-layered sac. Gastrulation. The formation of the gastrula. Gene. An hereditary unit which controls the appearance of definite characters. The genes are paired and are carried in the paired chromosomes, where they are situated at definite loci. Gene-complex. The interacting system produced by the whole of the genetic factors of an organism. These combine to make an internal environment in which any given factor must operate. Gene mutation. A change in a genetic factor. Genetics. The study of variation and heredity. Genetic factor. See ' Gene '. Genotype. An animal judged by its genetic constitution (com¬ pare Phenotype). Genotypic variation. Variation produced by changes (re¬ combinations or mutations) in the genes (compare Pheno- typic variation). Haploid cells. Those with a reduced number of chromosomes, as the reproductive cells. Heterogametic sex. That with dissimilar sex-chromosomes. H eterogonie growth. Disproportionate growth of the parts of an organism. Heteroploids. Individuals which contain a chromosome too few or too many. Heterozygote. An individual in which the members of a given pair of genes are dissimilar. Homogametic sex. That with similar sex-chromosomes. Homologous chromosomes. The members of the same chromo¬ some-pair. Homozygote. An individual in which the members of a given pair of genes are of similar nature. Leptotene stage. An early stage in the maturation of the germ cells in which the chromosomes become long thin threads.