File:Analysis of development (1955) (18170993461).jpg

Title: Analysis of development
Identifier: analysisofdevelo00will (find matches)
Year: 1955 (1950s)
Authors: Willier, Benjamin H. (Benjamin Harrison), b. 1890
Subjects: Embryology; Embryology
Publisher: Philadelphia, Saunders
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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/ o o\ / o O J 0 \ v ^ Q J Fig. 33. a, A haploid/diploid, white/dark mosaic axolotl from a cross between a white (recessive) female and a heterozygous dark male, at age of six months. Eye, gills, and limbs are smaller on haploid side (after Humphrey and Fankhauser, '43). b and c. Two possible explanations of origin of this mosaic, b, "Partial fertilization"; egg nucleus carrying factor for white first divided alone; left-hand cell produced haploid, white side of body; in right-hand cell, the other descendant of the egg nucleus fused with a sperm nucleus carrying the gene for dark and gave rise to the diploid, dark side. c, Dispermy; one sperm nucleus carrying gene for white divided independently and furnished the nuclei for the haploid, white side of the body; a second sperm nucleus with gene for dark fused with the egg nucleus giving rise to the diploid nuclei of the right, dark side. the meiotic divisions is suppressed so that tetraploid embryos are produced. In contrast to most balanced polyploids, aneuploids have a greatly reduced viability and are usually abnormal in appearance. The addition of as few as one or two chro- mosomes to the diploid complement disturbs the genie balance sufficiently to make normal development a rare event. Of 377 embryos with known aneuploid chromosome number only thirteen lived for periods of three months or more. The great majority showed typical abnormalities at an early stage. Most commonly the circulation was either not established at all or remained subnormal, with frequent stasis and hemorrhages in the eral effect on the development and main- tenance of the circulation which in turn creates the fluid imbalance. As might be expected, hypertriploid or near-tetraploid larvae are more viable and normal, since the unbalance created by the addition of single chromosomes to a multiple complement is less severe. None of the more viable hyperdiploids have reached sexual maturity so far. How- ever, offspring have been obtained from non- viable embryos by transplantation of gonad preprimordia to normal diploid embryos in the tail-bud stage. Chromosome Mosaics. In most of the species of amphibians investigated, embryos appear,

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