Skip to content
Login Register

#gene-centromere distance

2 public questions tagged with this topic.

Linkage Mapping and Tetrad analysis

If SDS frequency is 40%, distance between gene and centromere is

Given SDS frequency 40 percent among ordered octads scored in Neurospora, gene-centromere recombination equals half that value because only half chromatids recombinant per SDS tetrad with two parental two recombinant configuration. Therefore distance equals 20 percent or 20 centimorgans, representing moderate linkage to centromere. Calculation steps: percent SDS = number SDS asci divided total asci ×100 =40, then half =20 cM final distance. This distance lies within typical centromere-proximal to intermediate region demonstrating measurable linkage. Knowledge allows ordering genes relative centromere and predicting proportion FDS asci expected nearby.

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 5: SDS 40 Percent Maps To 20 cM Example

View Details
Linkage Mapping and Tetrad analysis

Distance between gene and centromere is calculated as

When second division segregation occurs, only two of four chromatids involved in single crossover become recombinant with respect centromere, two remain parental genotype. Recombination frequency therefore half of SDS asci proportion because half chromatids show recombination per tetrad. Map distance in centimorgans equals half percent SDS, calculated as percent SDS divided by two or SDS frequency ×50. Example illustrates 60 percent SDS corresponds 30 map units. Calculation assumes no chromatid interference and multiple crossovers rare. For very distal genes multiple exchanges may cause SDS plateau below theoretical 66 percent due to even crossovers.

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 5: Gene-Centromere Distance Half SDS Formula

View Details