Modifiers of heterocarpy determine capitulum size inMicroseris hybrid D 14 (Asteraceae — Lactuceae)
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The proportion of the outer, “hairy” achenes in capitula of hybrid D 14 (Microseris pygmaea × M. bigelovii) is determined by the same major gene as in its sister hybrid, B 87, as shown by marker segregation. Crossover between major gene and markers shows their genetic independence. Two modifiers segregating 9:7 influence the proportion of hairies in plants homozygous for the major gene. These same modifiers (or two genes linked with them) also determine the segregation of the number of achenes per head. Most likely, the modifiers act indirectly via a residual dependence of heterocarpy on capitulum size within strict quantitative limits set by the major gene. The identification of modifiers in a polygenic system as major genes for another character acting pleiotropically supports our contention that relatively few genes interact in plant development to determine key morphological characteristics at the organismic level.
Key WordsAngiosperms Asteraceae Lactuceae Microseris. — Heterocarpy canalized numbers meristic characters quantitative genetics modifier genes
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