A 1.6 kb deletion involving exons 1-4 of MCPH1.
MCPH1d1/MCPH1d2 animals are viable with an early maternal effect lethal phenotype.
The homozygous MCPH1d2 maternal effect lethal phenotype involves cell cycle arrest in a metaphase-like stage.
At early developmental stages, homozygous MCPH1d2 embryos lacking maternal MCPH1 display at most a narrow zone of clearing of cytoplasm around the egg periphery without pole cell formation or cellularisation.
Homozygous MCPH1d2 embryos lacking maternal MCPH1 show centrosomal abnormalities from the first mitotic cycle.