Size inheritance and growth in a mouse species cross (Mus musculus × Mus bactrianus). II. Birth weights

✍ Scribed by Green, C. V.

• Book ID: 102889869
• Publisher: John Wiley and Sons
• Year: 1931
• Tongue: English
• Weight: 581 KB
• Volume: 58
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/jez.1400580112

✦ Synopsis

Birth weights, like litter size, are determined by the interaction of two sets of factors: one, intrinsic, or genetic, and the other, extrinsic, or environmental.

Within the limits of normal variation, induced by environmental factors, the weight at birth of any mammal is characteristic of that particular form. The newly born offspring of the Perissodactyla and the Artiodactpla are large and well developed, while, on the other hand, bears, and especially the hfarsupialia, have extremely small, almost fetal, young. Within a single order considerable variation in size and precocity may occur. Among the Lagomorpha, the hares (Lepus) give birth to young fully furred and comparatively large, while the rabbits (e.g., Oryctolagus and Sylvilagus) produce blind and naked offspring. In the order Rodentia even greater differences occur. Guinea-pigs (Cavia) are large and so well developed at birth as to be nearly capable of independent existence. Mice (Mus), on the contrary, typifying the more usual situation in this order, are comparatively small at birth and are blind, naked, and helpless. Kope6 ( 2 4 ) , in comparing different races of rabbits, states that birth weight is in direct proportion to the average weight of the adult females of the breeds examined. I n mice a similar 'One of a series from a thesis submitted in partial fulfillment of the require-mat8 for the degree of Doctor of Philosophy in the Department of Zoology of the University of Michigan.