Naturally occurring haploids are mainly recorded in plants. The first report dates back to 1923, when haploid individuals were identified in Jimson weed. Haploidy also occurs in certain animal lineages. Most notable is the haploid sex determination system in Hymenoptera and Diptera, such as the honey bee, which is functionally haploid because males develop from unfertilized eggs. However, experimentally induced haploid animals, especially vertebrates, typically exhibit severe developmental defects collectively referred to as “haploid syndromes”, ultimately leading to fetal lethality.
New study published in KeAi journal reproduction and reproduction This reveals why haploid fish embryos cannot survive normal development. Researchers at Hunan Normal University created haploid zebrafish embryos by activating eggs with UV-treated sperm. Unlike normal embryos, which inherit two sets of chromosomes, these embryos had only one set.
We found that haploid embryos appear normal at very early stages of development. However, as development progressed, serious problems began to emerge. Many fetuses had curved body axes, swelling around the heart, decreased ability to swim, and died early. ”
Liangyue Peng, senior author and co-corresponding author
Notably, their rate of gastrulation and hatching was also much lower than that of normal diploid embryos. To investigate the cause, the researchers compared gene activity in three groups: haploid embryos, normal diploid embryos, and malformed diploid embryos.
“Using RNA sequencing, we identified 2,247 genes with altered activity, including 13 important genes consistently associated with abnormal development,” Peng added. “Further analysis showed that these genes are involved in several important biological processes, including developmental signaling, energy production, ion balance, and cell growth.”
In particular, this study points to disruptions in FGF and Wnt signaling pathways, mitochondrial translation, ion transport, and cell cycle control. Additionally, haploid syndromes do not appear to result from a single defect. Rather, it may be caused by a combined malfunction of multiple developmental and metabolic systems required for normal embryonic growth.
“Our findings help explain why haploid embryos are difficult to use in breeding and developmental studies, although they are useful for rapid genetic screening because recessive traits can be seen directly,” Peng said.
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Reference magazines:
Guo, X. others. (2026). Induction of haploid zebrafish and analysis of resulting developmental defects and aberrant gene expression. Reproduction and reproduction. DOI: 10.1016/j.repbre.2025.12.004. https://www.sciencedirect.com/science/article/pii/S2667071225000614?via%3Dihub
