Practice question

Parental ditype tetrad type contains spores all sharing parental allele combinations present in original cross parents, exemplified cross AB x ab producing ascus with two AB spores and two ab spores only, no Ab or aB recombinants. Such pattern arises when no exchange occurs between scored loci during meiosis, common for tightly linked genes with low recombination. Frequency PD high relative NPD signals linkage because parental chromatids preserved. Scoring PD requires ability distinguish parental haplotypes from recombinant haplotypes directly in haploid ascospores based on phenotype or molecular genotype analysis.