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#trans configuration

2 public questions tagged with this topic.

Linkage and Mapping

Recombination frequency is same in cis and trans because

Recombination frequency quantifies probability of exchange between two loci measured as proportion recombinant progeny. Exchange probability depends on physical length of DNA, chromatin structure, and map distance, not on how alleles are distributed across homologs in the parent. Cis AB/ab and trans Ab/aB both possess identical interlocus chromatin and identical chance of chiasma formation. Arrangement merely defines which gametes are labeled parental versus recombinant after meiosis in testcross. After correcting labeling, calculated RF identical because crossover mechanism occurs independently of allelic phase, reflecting conserved chromosome biology.

Ref: Hartl & Ruvolo, Genetics, 6th ed., Chapter 5: Recombination Frequency Independent of Coupling Phase

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Linkage and Mapping

In trans configuration, parental gametes are

Trans configuration also termed repulsion places dominant allele of one locus and recessive allele of second locus on same homolog, genotype written Ab / aB. During meiosis without crossing over between loci, these chromosomes segregate intact, so gametes carrying Ab and aB constitute parental nonrecombinant class observed at high frequency. Recombinant class AB and ab appears only after single crossover exchanges segments. Cis configuration AB/ab reverses parental identities but does not alter physical distance, therefore recombination frequency remains governed by interval length and chromatid interference, not by initial arrangement of alleles.

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 4: Cis-Trans Configurations and Gamete Types

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