Linkage disequilibrium — the nonrandom association of alleles at different loci — is a sensitive indicator of the population genetic forces that structure a genome. Given a multihybrid cross that obeys independent assortment and follows a dominant and recessive pattern, several generalized rules exist; you can use these rules to check your results as you work through genetics calculations ((Figure)). Now that you have struggled with a number of genetics problems, it may be worthwhile to make some generalizations about problem solving beyond what has been presented for each chapter so far. The first task always is to determine exactly what information has been presented and what is being asked. We show that this rule is inaccurate for intense selection and that a correct formula is L = 2σu (i) (1 - q (i)) w/ (z - x) = 2U w/ (z - x) = 2U/ (z - x + 2U) in which U is the mean number of new mutations per haploid genome in the population and w is the mean relative fitness before selection. You can start with any genotypes you want, but be sure to specify the phenotypes of individuals at each stage of the process. Outline the crosses similar to what is shown in Figure 7.8, and specify which progeny will be considered recombinant. Because human males need to inherit only one recessive mutant X allele to be affected, X-linked disorders are disproportionately observed in males. Females must inherit recessive X-linked alleles from both of their parents in order to express the trait. Genetic linkage analysis can be used to determine the order of genes on chromosomes. Closely linked genes are not segregating independently, like genes located on different chromosomes. This has different implications, e.g., in relation to trait correlations. Summary Note: As you will see below, when unaccounted for population structure is a concern, you will want to use KING for relationship filtering. In practice, KING tends to be more robust to unaccounted for population structure; whereas, such structure distorts GRM estimates. Please do not prune or filter any good SNPs that pass QC prior to any KING inference, unless the number of variants is too many to fit the computer memory, e.g., 100,000,000 as in a WGS study, in which case rare variants can be filtered out. If we want to measure recombination frequency between these genes, we first need to construct a fly in which we can observe recombination. That is, we need to make a fly that is not just heterozygous for both genes, but where we know exactly which genes are together on the chromosome.