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Biomedical subjects

R G Jaap

Publications and source records attributed to R G Jaap.

At least 19 recordsLinked to original sources
PubMed1979

Gametic products transmitted by chickens heterozygous for chromosomal rearrangements.

Chromosomal analysis was made from 3744 chick embryos derived from reciprocal matings between parents, one of which was heterozygous for a pericentric inversion, a centric fission, or one of three translocations. The objectives were to determine the types and frequencies of genetically balanced and unbalanced gametes transmitted to early embryos by rearrangement heterozygotes and to ascertain if some gametic types were preferentially produced or utilized. The array of embryos obtained from the heterozygous sires did not deviate significantly from the expected, except in the case of the centric fission group. Among embryos derived from heterozygous dams, however, significant deviations from the expected 1:1 ratio for complementary gametic products, resulting from specific balanced and unbalanced segregation types, were found consistently in all three translocation groups and the centric fission group (P less than 0.025). It was concluded that differences exist between heterozygous sires and dams in the frequencies at which some gametic types are produced. The deviations from the expected ratios among progeny of heterozygous dams may be the result of anaphase lagging during the meiotic division of oogenesis.

Animals↗
PubMed1978

The parental source of heteroploidy in chick embryos determined with chromosomally marked gametes.

Males homozygous for chromosomal translocations were mated to karyologically normal females. The resulting embryos, after incubation for 16-18 h, were prepared for cytogenetic analysis. Of the 62 embryos analysed, 54 (7.8%) were heteroploid or contained a major heteroploid cell line. Each of the 638 normal 2n embryos contained one marker and one normal chromosome, indicating that none arose from gynogenesis. Thirteen homogeneous haploid embryos were identified; 24 embryos were chimaeric 1n/2n and one was 1n/3n. All haploid cell lines contained a marker chromosome indicating androgenetic origins. The 9 homogeneous triploid (3n) embryos and the 3n cell line in a single 1n/3n embryo contained a single marker. All resulted from fertilization by single spermatozoon of eggs that were diploid as a result of suppression of the second meiotic division. The 3n lines of two 2n/3n embryos were derived from other mechanisms. A single homogeneous tetraploid (4n) embryo and the 4n cell lines of three 2n/4n mosaic embryos each contained two marker chromosomes and presumable resulted from failure of cytokinesis in an early cleavage division.

Animals↗
PubMed1977

Structural rearrangements of chromosomes in the domestic chicken: experimental production by X-irradiation of spermatozoa.

In order to produce chicks heterozygous for structural aberrations of chromosomes, 67 hens were inseminated with semen that had been exposed to 1200 R of X-rays. A sample of 204 chicks was hatched and survived. Among these, 18 (8.9%) contained rearrangements comprising 19 translocations and one pericentric inversion. All 10 males and eight females heterozygous for rearrangements were fertile and transmitted these rearrangements to approximately half their hatched progeny. Each of the major chromosomes of the chicken karyotype, except number 6, was involved in one or more of the translocations. The pericentric inversion was of a segment of chromosome number 2.

Animals↗
PubMed1976

Cytogenetic and phenotypic effects of a chromosomal rearrangement involving the Z-chromosome and micro-chromosome in the chicken.

Measurements demonstrated that the Z-chromosome was truly metacentric. Forty-six percent of one arm of a female's Z-chromosome had been translocated to a microchromosome (Z-micro) by irradiation of semen. The bread was 23 crossover units distal to the late feathering (K) locus. The barring (B) locus on the non-broken arm assorted almost independently of the Z-micro segment. Semen from eight sons of this Z-micro female was used to inseminate 98 dwarf (dw) broiler-type females. From karyotypes of 147 male and 149 female progeny, we identified 69 males heterozygous and 79 females hemizygous for Z-micro. Body weight of 43 males heterozygous for Z-micro was significantly greater than that of 45 normal Z paternal half-brothers at all ages from 2 to 24 weeks. In contrast, body weight of 57 Z-micro females compared with their 56 normal Z paternal half-sisters was depressed significantly at 2, 4, and 6 weeks but not significantly at 8, 12, 16, and 24 weeks of age. Age at first egg was retarded 8 days and egg production over a 153 day test period was reduced 19.6%, primarily due to a reduction of egg laying sequence from 2.7 to 2.1 days in the Z-micro females.

Animals↗
PubMed1975

Incidence and origin of heteroploidy, especially haploidy, in chick embryos from intraline and interline matings.

Preparations for chromosomal analysis were made from 2107 chick embryos at 16 hours of incubation. The embryos resulted from intraline and reciprocal interline matings of two genetically different stocks (AG and D6). The two stocks had been previously characterized as producers of high (AG) and low (D6) frequencies of chromosomally aberrant embryos. The overall frequency of aberrant embryos was 4.0 plus or minus 0.42%. The types and frequencies of abnormalities were: haploidy and haploid-euploid mosaics, 57%; polyploidy and polyploid-diploid mosaics, 19%; aneuploidy, 17%; aneuploid-diploid mosaics, 5%; and structural aberrations, 2%. Although there were no significant differences among the four types of matings in the overall frequency of heteroploid embryos (P greater than 0.1), a significant difference (P smaller than 0.01) in the frequency of haploid and haploid-euploid mosaic embryos was found. The difference was entirely attributable to the line of dam; D6 dams had 1.2% and AG dams had 2.7% haploid and haploid-euploid mosaic embryos. The difference between lines of sires was not significant. In addition, there was evidence of nonrandom distribution, among dams of both lines, of haploid and haploid-euploid mosaic embryos. It was concluded that the genotype of dam is an important influencing factor in the production of haploid cell lines in embryos. The superfluous genome in triploid embryos is usually maternal in origin, resulting from retention of the second polar body in the ovum. Sex-chromosome aneuploidy in chick embryos apparently derives from nondisjunction at meiosis I of oogenesis. The sex proportion of 2023 chromosomally sexed, diploid embryos was 50.2 plus or minus 1.1% male. No significant heterogeneity was observed among the types of matings. Sex proportion was not significantly influenced by any of a number of nongenetic variables.

Aneuploidy↗
PubMed1975

An attempt to force molt small egg-type pullets.

Small 1.1 kg. egg-type pullets having the sex-linked dw dwarfing gene were more resistant to a force molting program started at 11 months of age than were their 1.4 kg. non-dwarf counterparts. Water deprivation appeared to prevent egg production sooner in the dwarfs than in the non-dwarfs but egg production eight weeks after initiation of the force molt program was 46 per cent versus 64 per cent for the non-dwarf pullets.

Animal Feed↗
PubMed1975

Body growth response to selection and crossbreeding in dwarf and normal broiler-type chickens.

A normal-bodied broiler population and one dwarfed by the dw sex-linked gene were each sub-divided into two lines. AGB (normal) and D2B (dwarf) were selected only for superior body weight at eight weeks of age. AGE (normal) and D2E (dwarf) were sublines in which prospective dams were selected for large egg weight while prospective sires were selected for eight-week body weight. Selection for large eight-week weight of both sexes in both dwarf and normal populations during each of three generations resulted in superior growth rate to that observed when the dams were selected for egg weight. When the selected dams were tested each generation for their ability to produce superior broiler crossbreds using a commercial broiler sire strain, AGE proved superior to AGB in the second and third generations while D2B and D2E dams produced crossbreds with similar broiler weights. Normal-bodied dams which produced crossbreds having superior growth to that of the dwarf dams in the first generation lost most of this superiority by the third generation in sons and the second generation in daughters. Reproductive fitness was superior within the dwarf lines as well as in their ability to produce more crossbred progeny.

Animals↗