Plasmopara halstedii

Plasmopara halstedii is a eukaryotic plant pathogen that infects sunflower, causing sunflower downy mildew. Sunflower has evolved genes that confer resistance to downy mildew, called Pl genes, and breeding to spread the disease-resistant phenotype is a major method for controlling the disease in sunflower crops. Breeding programs in France in the 1980s were initially effective at controlling downy mildew. However, by the 1990s and 2000s, populations of P. halstedii had overcome several of the resistance genes. Additionally, while only one pathotype of P. halstedii existed in France until 1988, twenty years later 14 pathotypes could be found throughout France.

Researchers collected DNA from 24 samples of P. halstedii isolated from infected sunflowers for population genetic analysis. They analyzed data from 12 genetic markers, including one called Pha43, which had two alleles, called R and r. The genotype data from Pha43are shown in the table below.

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Genotype Count
RR 13
rr 9
Rr 2
Total 24

Data: Delmotte et al. (2008). Infection, Genetics and Evolution.

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Using the observed genotype data, answer the following questions.

Based on the frequency of the R and the r alleles, what is the expected frequency of the Rr genotype in Hardy-Weinberg equilibrium?

What is the observed frequency of the RR genotype in the French P. halstedii population?

What is the observed frequency of the rr genotype in the French P. halstedii population?

What is the observed frequency of the Rr genotype in the French P. halstedii population?

Do these data indicate that the population is in Hardy-Weinberg equilibrium for the Pha43 marker?

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