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Genetics: crossing over and expected progeny?
In corn, small pollen (sp) is recessive to normal pollen (sp+) and banded necrotic tissue, called zebra necrotic (zn), is recessive to normal tissue (zn+). The genes that produce these phenotypes are 12 m.u. (map units) apart on chromosome 10. If crossing over occurs between these two loci, give the types of progeny expected from the following crosses: 1) sp+ zn+ / sp zn X sp zn / sp zn
2) sp+ zn / sp zn X sp zn / sp zn
1 Answer
- Asst ProfLv 71 decade agoFavorite Answer
Using s for sp, z for zn, and + for dominant, wild type:
1) the parental cross is +s+z x sszz, so this is a 1x4 Punnett square-- the gametes are ++, +z, s+, and sz AND sz. You will get all 4 possible combinations of progeny. The cross-over phenotypes, +s and +z will make up 12% of the progeny.
2) the parental cross is +szz x sszz, so this is a 1x2 Punnett square-- the gametes are +z an sz AND sz. There will be two kinds of progeny, split 50/50, +szz and sszz