Summary. Chromosomal analyses were made of 463 rabbit blastocysts drawn from thirty-nine superovulated does of four strains. Semen containing 1\m=.\5%diploid spermatozoa was taken from one strain only. Artificial insemination was conducted with untreated semen or with centrifuged fractions containing either 0\m=.\4%or 2\m=.\9%diploid spermatozoa. The results indicate that diploid spermatozoa are not a major cause of triploidy among embryos. The sex ratio scored chromosomally among 434 diploid blastocysts was 48\m=.\62(\m=+-\2\m=.\40)%males. With data in the literature incorporated, the average sex ratio among 1077 blastocysts (consistent over three species of mammal) became 50\m=.\42 (\m=+-\1\m=.\52)% males. These figures may be taken to estimate the primary sex ratio. Sex ratio among blastocysts is extremely stable over various biological and experimental conditions. Twenty-three (5%) of the 463 analysable blastocysts were heteroploid. They comprised eight triploids (5 XXX, 3 XXY), four trisomics, four diploid/trisomic mosaics, one diploid/monosomic mosaic, four diploid/ tetraploid mosaics, one diploid/triploid mosaic and one triploid/ hexaploid mosaic. `Clustering' of heteroploids occurred in particular dams. Superovulation had no demonstrable effect on the incidence of heteroploidy. There is some evidence of genetic (dam strain) effects on the incidence.

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Chromosomal abnormalities and sex ratio in rabbit blastocysts

Germ cell transplantation and testis tissue xenografting in domestic animals.

Chromosome aberrations and their influence on the reproductive performance of domestic animals - a review

Sex chromosome divergence, which follows the cessation of recombination and degeneration of the sex-limited chromosome, can cause a reduction in expression level for sex-linked genes in the heterozygous sex, unless some mechanisms of dosage compensation develops to counter the reduction in gene dose. Because large-scale perturbations in expression levels arising from changes in gene dose might have strong deleterious effects, the evolutionary response should be strong. However, in birds and in at least some other female heterogametic organisms, wholesale sex chromosome dosage compensation does not seem to occur. Using RNA-seq of multiple tissues and individuals, we investigated male and female expression levels of Z-linked and autosomal genes in the collared flycatcher, a bird for which a draft genome sequence recently has been reported. We found that male expression of Z-linked genes was on average 50% higher than female expression, although there was considerable variation in the male-to-female ratio among genes. The ratio for individual genes was well correlated among tissues and there was also a correlation in the extent of compensation between flycatcher and chicken orthologs. The relative excess of male expression was positively correlated with expression breadth, expression level, and number of interacting proteins (protein connectivity), and negatively correlated with variance in expression. These observations lead to a model of compensation occurring on a gene-by-gene basis, supported by an absence of clustering of genes on the Z chromosome with respect to the extent of compensation. Equal mean expression level of autosomal and Z-linked genes in males, and 50% higher expression of autosomal than Z-linked genes in females, is compatible with that partial compensation is achieved by hypertranscription from females’ single Z chromosome. A comparison with male-to-female expression ratios in orthologous Z-linked genes of ostriches, where Z–W recombination still occurs, suggests that male-biased expression of Z-linked genes is a derived trait after avian sex chromosome divergence.

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Transcriptome sequencing reveals the character of incomplete dosage compensation across multiple tissues in flycatchers.

Origins of Heteroploidy in Chicken Embryos

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R. C. Miller

Papers

Sex proportion of domestic chicken at 16 hours of incubation

Deletion, Monosomy, and Multiple Monosomy-Trisomy Mosaicism in Chicken Embryos