Summary 1. The action of the gene on the characters of an animal is limited to those manifestations which are physiologically possible if the gene is to survive. Environmental conditions affecting the physiology of the animal will therefore have a selective action on those genes which give rise to characters in harmony with the environment concerned. The main problem in animal breeding is to be able to direct the course of evolution and to select genes giving rise to increased development of certain characters. 2. Where the development of a character is limited by environmental conditions it is not possible to select for genes which have the capacity of manifesting themselves in excess of these environmental limitations. If, therefore, the physiological factor limiting this manifestation of the gene is removed by placing the animal under optimal conditions for the development of the character in question, then it is possible to select for genes giving a higher level of production. 3. Owing to conditions affecting survival rate at birth, genetic control of reproduction has, under natural conditions, often become linked to variation in daylight hours. Egg production in hens depends on increasing hours of daylight and in sheep on decreasing hours, varying in degree according to the latitude of origin of the breed. Before progress can be made in the selection of genes concerned with this, the survival rate at birth has to be regulated by the control of environmental conditions. 4. Most commercially valuable characters in animals are quantitative rather than qualitative, so that it is the degree to which the character is manifest that is important. In breeding for high milk yield various physiological factors (letting down of milk, food intake before and after parturition, milk pressure, etc.) have in turn become limiting factors for further increase in yields, and further genetic selection for increased yields has not been possible until appropriate action has been taken to eliminate these limiting factors. 5. A disadvantage of the method of selection within a specially controlled environment is that the environmental conditions limit the scope of the genetic characters that can be selected for effectively. Thus selection for high milk yields in temperate climates is not directly applicable to tropical climates, for factors regulating body temperature in high air temperatures have not been selected for, and in tropical climates combination with genes for this latter character must be made before the genes for high milk production become effective. 6. In the selection of genes for meat production and growth the control of the plane of nutrition during the different phases of growth is important, for by this means control of the body proportions is obtained. The natural nutritive conditions under which the specialized breeds of pork, bacon, lard and native pigs have been produced, when repeated under experimental conditions on inbred lines, give the same types of individuals as before. Genetic selection would appear to...

Academic studies and traditional breeding of yeasts depend upon their sporulation lifestyle. The strains used have been specially selected to sporulate readily and to mate producing new yeast types. Unfortunately brewing yeast strains do not behave in this way. They sporulate poorly, any spores which are formed are usually non-viable and any haploid strains produced are invariably non-maters. Only in recent years, with the development of recombinant-DNA techniques, has the specific breeding of new brewing yeast strains become widespread. Strains have been produced with the ability to ferment a wider range of carbohydrates, with altered flocculation properties and which produce beers with modified flavours. Many have been tested on the pilot scale and one, an amylolytic brewing yeast, has received approval for commercial use.

Ewes. There was some variation from year to year in the times of onset and end of the breeding season; on the average it was evenly spaced on either side of the shortest day. Occasionally ewes were served and became pregnant at times well outside the normal limits of the breeding season. Lambs were allowed to suckle the ewes for as long as they would; when lambing occurred more than about 100 days from the start of the season there was no delay in onset of heat in the ewe. When lambing was later there was some delay, but the duration of the lactation anoestrum shortened to a minimum near the middle of the season and then lengthened again.In the first half of the season the period of the oestrous cycle lengthened slowly and steadily; in the second part it became more variable, there was first a slight shortening, but upon the whole it continued to increase in length. From the start of the season the frequency of twinning increased quickly to a peak in about November and then declined for the rest of the season. At the end of the season there was a high proportion of services not fertile.Lambs. Growth in the first 2 months was greatest in those born in May; in the fourth to sixth months it was greatest in the earliest born and least in the latest, the highest weight at 6 months old being reached by those earliest born.

Fermentation performance (defined as the time required, in hours, to attenuate an all malt wort from OG 1040°to 1020°) can be accurately predicted for Saccharomyces cerevisiae NCYC 1681 using the Acidification Power test (r =0 943, p = <0 001: 37 samples). The results obtained with four other yeasts suggest that the test has wide applicability. The test measures the ability of a population of yeast cells to maintain different intracellular and extracellular hydrogen ion concentrations when placed in distilled water. It also measures the change in these concentr ations induced by the presence of glucose. The method is reproducible (standard deviation of the mean =0 61 %) and is unaffected by variations of ±11 % of yeast weight in the assay, this makes the Acidification Power test a 'stand alone' test, no secondary analyses (such as dry weight determination) are necessary. The test can be performed using common laboratory equipment and can be applied routinely in breweries for yeast selection based on the use of Reject Quality Limits (RQL). In addition, the technique may find application in the evaluation of yeast handling protocols, in the assessment of new or novel yeast strains, and in the assessment of yeast condition prior to acid washing.