Simulation of chromosomal homology searching in meiotic pairing.

A cellular automaton model has been developed to simulate some aspects of chromosome behaviour during meiotic prophase when homologous chromosomes search for each other so that they can pair. Simulations allow one to compare the relative efficiencies of random searching by chromosome shuffling along the inner nuclear membrane or within the lumen of the nucleus, the effects of biased movements and of chromosome clustering (bouquet or synizetic knot), different numbers of homology recognition sites per chromosome and different chromosome numbers on the efficiency of the pairing process. Parameters of the simulated models can be easily adjusted to fit experimentally obtained figures.

[A thermodynamic model to predict oxygen consumption and peripheral blood flow in the newborn infant. II. Its validity under steady-state conditions]. / Ein thermodynamisches Modell zur Beurteilung des Sauerstoffverbrauches und des peripheren Blutflusses beim Neugeborenen. II. Seine Gültigkeit unter Gleichgewichtsbedingungen.

A thermodynamic model, which allows to predict oxygen consumption and peripheral blood flow from temperature measurements, was tested for its validity in newborn infants. This model is based on the close relation between 1) oxygen consumption and heat production and 2) between circulation and heat convection. In this model 3 temperatures on the patient, 2 temperatures in the environment and geometrical variables (weight, length) are measured and known physiological relations used to calculate oxygen consumption (VO2) and peripheral blood flow (pBF). In 15 newborns the VO2 was synchroneously determined by means of the flow-trough method and the thermomodel. The VO2 and the VO2/kg bodyweight respectively correlated significantly (p less than 0.01) with the directly measured VO2 (correlation coefficients r 0.89 and 0.66 respectively). In 12 newborns the peripheral blood flow was synchroneously determined by means of the impedance plethysmography and the thermomodel. The directly measured peripheral blood flow correlated significantly (p less than 0.001) with the peripheral heat flow (r = 0.73, 34 measurements) and with the peripheral blood flow (r = 0.86, 34 measurements) both obtained from the thermomodel. The values of VO2 and pBF obtained by direct measurement and by the thermomodel are as closely correlated as values which were obtained comparing two conventional methods. These results demonstrate the validity of the theoretical model being suitable for clinical use to continuously predict VO2 and pBF.

[The determination of oxygen consumption from temperature measurements with the use of a thermodynamic model ]. / Die Bestimmung des Sauerstoffverbrauchs bei Neugeborenen aus Temperaturmessungen unter Zuhilfenahme eines thermodynamischen Modells.

A thermodynamic model is described which allows to calculate the oxygen consumption from 4 temperatures as input-variables. These input-variables are: one core-temperature (Tesoph), two skin-temperatures (one at the chest, one at the calf) and the incubator-air temperature. This model is based on the close relationship between oxygen consumption and heat production. The rate of heat production is derived from heat loss to the environment plus heat storage in the body. The data are smoothened by a special mathematical procedure and processed by a HP-85 Computer. Oxygen consumption was synchronously determined by the thermodynamic model and by a conventional method 155 times in four newborns. The flow-through method was used as conventional reference method. The results show that the thermodynamic model yields values for oxygen consumption which are closely related to directly measured values; which indicate the increase in oxygen consumption with activity and decreased environmental temperature; and which follow rapid changes in oxygen consumption of 5 ml/kg per minute. Consequently this thermodynamic model seems suitable to predict the relative changes in oxygen consumption. However the absolute values of oxygen consumption obtained by the model and obtained by direct measurement differ by 5 to 25% the thermodynamic model yielding systematically higher values than the direct measurement. The reasons for this difference are discussed. We demonstrated that a maximum of reliable information can be obtained from a minimal number of measuring sites on the patient by using a theoretical-analytical model.

[A thermodynamic model to predict oxygen consumption and peripheral blood flow of the newborn infant (author's transl)]. / Ein thermodynamisches Modell zur Beurteilung des Sauerstoffverbrauches und des peripheren Blutflusses beim Neugeborenen.

The continuous evaluation of the oxygen consumption and peripheral blood flow is technically difficult and practically not feasible in the newborn infant. We attempted to assess these two variables by means of a thermodynamic model, where only a set of geometrical variables and a set of temperatures have to be measured. The body is represented by a central cylinder (head, trunk) and a peripheral cylinder (extremities) and the heat flux therein is described by mathematical formulas. Only steady state conditions are considered. From the heat flux "surface leads to environment" the oxygen consumption and from the heat flux "central cylinder leads to peripheral cylinder" the peripheral blood flow is derived. On the patient only one core temperature (rectum) and two skin temperatures--one on the chest and the other one on the calf--have to be measured. The validity of the model was tested in 17 healthy newborns (body weight 1,100-3,850 g) and 6 diseased newborns (body weight 1,500-3,400 g). Comparing the computed oxygen consumption to values from the literature for a similar group showed good agreement. In 7 newborns the calculated oxygen consumption correlated well (r = 0.88, p less than 0.01) with the directly and synchroneously measured oxygen consumption. Indirect proof that the model also gives a reasonable index for the peripheral blood flow was obtained by relating the computed peripheral blood flow a) to values from the literature for a similar group and b) by demonstrating the dependence of the (calculated) peripheral blood flow on the haematocrit (r = -0.58, p less than 0.01).

A remark on the notions of gene and gametic frequencies for sex-linked genes.

A general model describing the evolution of genotypic frequencies at a heterosomal locus with n alleles is introduced. The treatment includes as a special case the standard derivation for X-linked loci as well as different concepts encountered in the literature which seem to contradict this derivation. The disagreement, however, is easily solved by distinguishing between gene and gametic frequencies.