Chromosomal Abnormalities and Sex Ratio in Rabbit Blastocysts

Abstract

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.`C lustering' 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.

Karyotypes of 3- or 4-day-old pig embryos after short in-vitro culture

“…Fechheimer & Beatty (1974) and Hare & Singh (1979) give modes of origin of this abnormality. The fact that Hare et al (1980) did not obtain pregnancy after transfer of this type of embryo to pseudopregnant cattle does not prove the karyotype to be an embryonic lethal.…”

“…In man, there is a coincidence between a high level of chromosome abnormalities amongst early conceptuses and a high level of prenatal death. Experimental animals such as the mouse, the Syrian hamster and the rabbit are characterized by lower levels of embryonic wastage and the frequencies of chromosome abnor¬ malities amongst pronucleate eggs and young blastocysts are also low (rabbit: Fechheimer & Beatty, 1974;mouse: Fraser & Maudlin, 1979; Syrian hamster: Martin, Balkan & Burns, 1983).…”

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

“…Equal numbers were ZWW and ZZZ and all 10 can be considered as resulting from suppres¬ sion of MIL The rarity of a diandric origin of triploidy in birds is in contrast to the situation in mammals. Beatty (1974) (Austin, 1961 ;Fechheimer & Beatty, 1974). Clearly no single mechanism is sufficient to account for the various types of 2n/3n chick embryos which have so far been reported.…”

“…In man and other mammals the occurrence of heteroploid chromo¬ some complements in embryos is perhaps the most important cause of abortion or embryonic death : it has been estimated that 60% of spontaneous abortions are the direct result of chromosomal ab¬ normalities of the afflicted embryos (see Boué, Boué & Lazar, 1975, for basis of this estimate). Chromosomal analysis of preimplantation mouse, rabbit, hamster and rat embryos also shows that a relatively high proportion die early because of chromosomal abnormality (Butcher & Fugo, 1967;Vickers, 1969;Shaver & Carr, 1969;Kaufman, 1973 ;Yamamoto, 1973 ;Fechheimer & Beatty, 1974). Each species exhibits a unique array of heteroploid types reflecting its individual susceptibilities to errors of the reproductive process which result in chromosomal abnormalities (Ford, 1975).…”

The survival and transport to the site of fertilization of diploid rabbit spermatozoa

“…However, such triploids as are found in the rabbit are most probably due to chromosome doubling in the oocyte rather than to fertilization by diploid sperma¬ tozoa (Fechheimer & Beatty, 1974;Beatty, 1974). Therefore The present study was designed to determine whether diploid rabbit spermatozoa are as successful as haploids in reaching the site of fertilization, with special reference to any possible selectivity of sperm transport within the female reproductive tract.…”