Male mice can grow female organs — if their mothers lack iron

Jun 4, 2025

Iron deficiency in mother mice can lead to male offspring developing female sex organs, challenging traditional genetic beliefs. This highlights the complex interplay between maternal nutrition and sex determination. Research also reveals the vital role of small-scale fishers, who contribute significantly to global nutrition and sustainable practices. Additionally, fascinating discoveries about protein ambidexterity and the unique eyesight of humpback whales shed light on evolutionary adaptations and the challenges faced by these majestic creatures in their environment.

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INSIGHT

Iron disrupts mice sex determination

Iron deficiency in pregnant mice can cause genetically male offspring to develop female sex organs.
This happens because iron is needed for an enzyme that activates the male sex gene SRY.

INSIGHT

Sex determination is multifactorial

Iron is one factor influencing sex determination; it's more complex than genetics alone.
Environmental factors like iron levels can play a significant role in mammalian sex development.

INSIGHT

Iron's pregnancy role spans mammals

Though mice and humans differ, iron's role in pregnancy is crucial across mammals.
Iron deficiency during pregnancy has important consequences even if the exact effects on human sex determination are unclear.

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00:45 Iron’s role in mice sex determination

Iron deficiency in mice mothers can sometimes result in their offspring developing female sex organs despite having male sex genes, according to new research. While genetics has been thought to be the primary factor in determining offspring sex in mammals, the new work shows that a lack of iron disrupts an enzyme involved in the development of testes, leading to some mice with male sex-determining genes being born with female genitalia and ovaries. This suggests that sex determination is controlled by more than genetics, but more work will need to be done to understand the precise mechanisms involved.

News: Male mice can grow ovaries if their pregnant mums are iron deficient

Research article: Okashita et al.

06:31 Research Highlights

How climate change is making dust storms more likely, and understanding the genetics of a boy who couldn’t feel pain.

Research Highlight: The perfect storm for dust storms, thanks to global warming

Research Highlight: CRISPR helps to show why a boy felt no pain

08:51 The role of small-scale fishers in sustainability

The contributions that small-scale fishers make to sustainable fishing have been described as ‘invisible’, but now a huge research project has revealed the role this community plays in feeding populations and protecting oceans. Looking at data from 58 countries, researchers have shown that small-scale fishers account for around 40% of the global catch and feed approximately 25% of the world’s population. The people behind the initiative hope that these data can help give a voice to small-scale fishers as people look for ways to feed the world sustainably.

Immersive : Small-scale fisheries

19:44 Briefing Chat

The discovery of an ‘ambidextrous’ protein; and why humpback whales, despite their enormous eyes, appear to be shortsighted.

Nature: Rare ‘ambidextrous’ protein breaks rules of handedness

Discover Magazine: Big Eyes, Blurry Vision: Why Humpback Whales Struggle to See Clearly

Subscribe to Nature Briefing, an unmissable daily round-up of science news, opinion and analysis free in your inbox every weekday.

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