the synaptonemal complex. The synaptonemal complex is a critical component for c
ID: 205671 • Letter: T
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the synaptonemal complex. The synaptonemal complex is a critical component for chromosome pairing, segregation, and recombination. We previously identified a novel germ cell-specific HORMA domain encoding gene, Hormad1, a member of the synaptonemal complex and a mammalian counterpart to the yeast meiotic HORMA domain protein Hop1. Hormad1 is essential for mammalian gametogenesis as knockout male and female mice are infertile. Hormad1 deficient (Hormad1) ( testes exhibit meiotic arrest in the early pachytene stage, and synaptonemal complexes cannot be visualized by electron microscopy. Hormad1 deficiency does not affect localization of other synaptonemal complex proteins, SYCP2 and SYCP3, but disrupts homologous chromosome pairing. Double stranded break formation and early recombination events are disrupted in Hormad1(-/) (-) testes and ovaries as shown by the drastic decrease in the yH2AX, DMC1, RAD51, and RPA foci. HORMAD1 co-localizes with yH2AX to the sex body during pachytene. BRCA1, ATR, and yH2AX co-localize to the sex body and participate in meiotic sex chromosome inactivation and transcriptional silencing. Hormad1 deficiency abolishes yH2AX, ATR, and BRCA1 localization to the sex chromosomes and causes transcriptional de-repression on the X chromosome. Unlike testes, Hormad 1 (-/)(-)ovaries have seemingly normal ovarian folliculogenesis after puberty. However, embryos generated from Hormad1(-)) oocytes are hyper- and hypodiploid at the 2 cell and 8 cell stage, and they arrest at the blastocyst stage. HORMAD1 is therefore a critical component of the synaptonemal complex that affects synapsis, recombination, and meiotic sex chromosome inactivation and transcriptional silencingExplanation / Answer
1) According to the passage given above, the author used targeted null or knockout mutation to create a frameshift mutation in order to obtain Hormad1 deficient mice.
2) Mutated mice are all Hormad1 knockouts, hence their genotype is Hormad1 (-/) (-)
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