Genes E and H are syntenic in an experimental organism with the genotype EH/eh. Assume that during each meiosis, one crossover occurs between these genes. No homologous chromosomes escape crossover, and none undergo double crossover. Are genes E and H genetically linked? Why or why not? What is the proportion of parental gametes produced by meiosis?

Why does more crossing over occur between two distantly linked genes than between two genes that are very close together on the same chromosome?

Explain why a 50 percent recovery of single-crossover products is the upper limit, even when crossing over always occurs between two linked genes?

Why are double-crossover events expected less frequently than single-crossover events?

What two essential criteria must be met in order to execute a successful mapping cross?

Alleles A and a are on one pair of autosomes, and alleles B and b are on a separate pair of autosomes. Does crossover between one pair of homologs affect the expected proportions of gamete genotypes? Why or why not? Does crossover between both pairs of chromosomes affect the expected gamete proportions? Why or why not?

You have isolated (1) a streptomycin-resistant mutant (strᴿ) of Chlamydomonas that maps to the chloroplast genome and (2) a hygromycin-resistant mutant (hygᴿ) of Chlamydomonas that maps to the mitochondrial genome. What types of progeny do you expect from the following reciprocal crosses?

mt⁺ strᴿ hygˢ× mt⁻ strˢ hygᴿ

mt⁺ strˢ hygᴿ× mt⁻ strᴿ hygSˢ

Two different female Drosophila were isolated, each heterozygous for the autosomally linked genes b (black body), d (dachs tarsus), and c (curved wings). These genes are in the order d–b–c, with b being closer to d than to c. Shown here is the genotypic arrangement for each female along with the various gametes formed by both:

Identify which categories are noncrossovers (NCOs), single crossovers (SCOs), and double crossovers (DCOs) in each case. Then, indicate the relative frequency in which each will be produced.