Meiotic crossovers characterized by haplotype-specific chromosome painting in maize

Meiotic crossovers (COs) play a critical role in generating genetic variation and maintaining faithful segregation of homologous chromosomes during meiosis. We develop a haplotype-specific fluorescence in situ hybridization (FISH) technique that allows visualization of COs directly on metaphase chromosomes. Oligonucleotides (oligos) specific to chromosome 10 of maize inbreds B73 and Mo17, respectively, are synthesized and labeled as FISH probes. The parental and recombinant chromosome 10 in B73 x Mo17 F1 hybrids and F2 progenies can be unambiguously identified by haplotype-specific FISH. Analysis of 58 F2 plants reveals lack of COs in the entire proximal half of chromosome 10. However, we detect COs located in regions very close to the centromere in recombinant inbred lines from an intermated B73 x Mo17 population, suggesting effective accumulation of COs in recombination-suppressed chromosomal regions through intermating and the potential to generate favorable allelic combinations of genes residing in these regions.

Inversions

Inversions are intrachromosomal structural rearrangements. The most common is the simple (or single) inversion. If the inversion coexists with another rearrangement in the same chromosome, it is a complex inversion. In an inversion, a segment of chromosome is switched 180 degrees. If this segment includes the centromere, this is a pericentric inversion; if not, it is a paracentric inversion. In principle, and almost always in practice, it is only the pericentric inversion that conveys an important genetic risk to carriers of the inversion: Their children may inherit a “recombinant” chromosome that would inevitably be imbalanced. This chapter considers these two type of inversions and discusses the degree of genetic risk that may—or may not—be associated.

Pericentric Inversion in Chromosome 10 in a Girl, Inherited from a Phenotypically Normal Mother: Case Report and Literature Review

Pericentric inversions in chromosome 10 are regarded as both common and rare conditions, based on breakage and rearrangement within each specific segment. We present phenotypic and cytogenetic characterizations of a rare recombinant chromosome 10, namely inv(10)(p11q26), in a 13-month-old flabby girl associated with a maternal pericentric inversion. A review of the literature on the different aspects of this condition is also provided.

Defining the Role of the MADS-Box Gene, Zea Agamous-like1, a Target of Selection During Maize Domestication

Genomic scans for genes that show the signature of past selection have been widely applied to a number of species and have identified a large number of selection candidate genes. In cultivated maize (Zea mays ssp. mays) selection scans have identified several hundred candidate domestication genes by comparing nucleotide diversity and differentiation between maize and its progenitor, teosinte (Z. mays ssp. parviglumis). One of these is a gene called zea agamous-like1 (zagl1), a MADS-box transcription factor, that is known for its function in the control of flowering time. To determine the trait(s) controlled by zagl1 that was (were) the target(s) of selection during maize domestication, we created a set of recombinant chromosome isogenic lines that differ for the maize versus teosinte alleles of zagl1 and which carry cross-overs between zagl1 and its neighbor genes. These lines were grown in a randomized trial and scored for flowering time and domestication related traits. The results indicated that the maize versus teosinte alleles of zagl1 affect flowering time as expected, as well as multiple traits related to ear size with the maize allele conferring larger ears with more kernels. Our results suggest that zagl1 may have been under selection during domestication to increase the size of the maize ear.

A Peruvian Child with 18p-/18q+ Syndrome and Persistent Microscopic Hematuria

Chromosome 18 pericentric inversion carriers could have offspring with recombinant chromosomes, leading to patients with clinical variable manifestations. Patients with 18p-/18q+ rearrangements share some clinical characteristics, while other characteristics differ. Factors for such divergence include the length of the inverted segment, among others. Here, we describe a Peruvian child with dysmorphic features, intellectual disability persistent microscopic hematuria, aortic pseudocoarctation, and descending aorta arteritis, among others. Karyotype analysis of family members determined the mother as the carrier of a pericentric inversion: 18[inv(18)(p11.2q21.3)]. This child carries a recombinant chromosome 18, with chromosomal microarray analysis detecting two genomic imbalances in patient's chromosome 18: one duplicated region and one deleted segment in the large and the short arms, respectively. Persistent microscopic hematuria has not been reported among 18p-/18q+ phenotypes. Our patient elucidates that other factors play significant and yet unknown roles for not fulfilling the proposed genotype–phenotype correlation associated with hemizygosity in this type of recombinant chromosome 18 or presenting these features as the patient ages.