all embryos are female

Introduction

The sex ratio and development of human embryos have been subjects of extensive research, particularly in the context of embryonic stem cell lines and early embryonic development. Understanding the factors influencing the predominance of female embryos and the physiological differences between male and female embryos can provide insights into reproductive biology and assisted reproductive technologies.

Key Insights

Female Bias in Embryonic Stem Cell Lines:
- There is a significant increase in female human embryonic stem cell (HESC) lines derived from preimplantation genetic diagnosis (PGD) and in vitro fertilization (IVF) embryos, attributed to suboptimal culture conditions rather than a true gender imbalance in the embryos used for derivation.
Sex Ratio in Early Embryos:
- Histological analysis of human embryonal gonads from induced abortions shows a higher male-to-female ratio at earlier gestational stages, suggesting that the primary sex ratio may be higher than the secondary ratio observed at birth.
Gene Expression Differences:
- In mouse embryos, the Fthl17 gene family, which is X-linked and imprinted, shows predominantly female expression following the two-cell stage, indicating early sex differences in gene expression before gonadal differentiation.
Sex-Related Physiology:
- Male and female preimplantation embryos exhibit differences in their proteome and metabolome due to the period when both X chromosomes are active. These differences manifest in altered enzyme activity and metabolic pathways, affecting nutrient utilization and growth rates.
Embryo Development Kinetics:
- Studies using time-lapse systems to analyze embryo development kinetics show significant similarities in timings related to the female component, although no specific intrinsic female factors were identified. Sperm quality, such as oligozoospermia, can influence early embryonic development timings.

Conclusion

Research indicates a notable female bias in human embryonic stem cell lines, likely due to culture conditions rather than an inherent gender imbalance. Early-stage embryos exhibit sex-specific differences in gene expression and metabolic activity, with male embryos being more prevalent at earlier gestational stages. These findings highlight the complex interplay of genetic and environmental factors in embryonic development and the importance of considering sex differences in reproductive biology studies.

All embryos are female

Summary

Introduction

Key Insights

Conclusion

Sources and full results

Female sex bias in human embryonic stem cell lines.

Female preponderance in human embryonic stem cell lines is due to suboptimal culture conditions, rather than a true gender imbalance in embryos used for derivation.

Analysis and quantification of female and male contributions to the first stages of embryonic kinetics: study from a time-lapse system

Sperm may have an early embryonic effect, but no specific female factors were identified in this study.

Sex ratio in human embryos obtained from induced abortion: histological examination of the gonad in 1,452 cases.

The earlier in gestation, the higher the sex ratio of human embryos, suggesting that the primary sex ratio may be higher than the secondary ratio of 106 males to 100 females at birth.

The X-linked imprinted gene family Fthl17 shows predominantly female expression following the two-cell stage in mouse embryos

By the two-cell stage in mouse embryos, the Fthl17 gene family shows predominantly female expression, indicating early sex differentiation occurs before gonad differentiation.

Sex-related physiology of the preimplantation embryo.

Male and female preimplantation embryos exhibit differences in their cellular phenotype, including altered enzyme activity and metabolic pathways, which may influence their growth rates and potential for identifying sex differences in human embryos.

Female bovine blastocysts are more prone to apoptosis than male ones.

Female bovine blastocysts are more prone to apoptosis than male ones, with a more pronounced difference in apoptosis when cultured in fetal calf serum, especially in small blastocysts.

Comparison of gender-specific human embryo development characteristics by time-lapse technology.

Female and male human embryos show similar cell division kinetics, but female embryos show earlier cavitation, but these results are not statistically significant.

Sexing of Live Rabbit Blastocysts

Fluorescence microscopy can identify male and female rabbit embryos within five days of conception, potentially benefiting agriculture and human affairs.

Experimental Intersexuality: The Relative Sensitivity of Male and Female Rat Embryos to Administered Estrogens and Androgens

Male and female rat embryos show mutually antagonistic effects on sexual structure differentiation, with estrogens nullifying masculinizing effects of androgens and androgens nullifying feminizing effects of estrogens.

Apomixis: Embryo Sacs and Embryos Formed without Meiosis or Fertilization in Ovules.

Apomictic reproduction in flowering plants produces genetically identical embryos, offering potential for high-yielding food crops and a sustainable method for perpetuating a given genotype.

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