c-ray
04-30-2006, 07:19 PM
Effective breeding population is one of the most basic parameters of population genetics. The idealised Ne is by definition infinitely large and diverse and fully represents all the potential genetic expressions in the population.
The actual calculation is fairly simple arithmetic and goes as follows:
Ne = 4 * (# of Males) * (# of Females) / (# of Males) + (# of Females)
For example a grower selects 1 male and 500 females for breeding. The effective breeding population is; (4) * (1) * (500) / (500+1) = 4. The effective breeding population can never be larger than the number of males selected for breeding. Another example 50 males 10 females Ne becomes 2000/60 or 33.33.
I read the article by DJ Short regarding his breeding of the famous Blueberry wherein he states that he only uses one male for his breeding selections. That might help explain why Blueberry is so resistant to breeding improvement. To quote, "Second, I select only one male from any single breeding project. Again, this simplifies things and avoids mistakes enormously. That male is generally selected at about the third week in the flowering cycle, unless it is a clone from another project".
By and large most cannabis breeders tend to ignore matters like effective breeding population when making their selections for males.
To expand on the basic concept of Ne one must consider how Ne effects the F statistic (Coefficient of Inbreeding).
So let's assume an NE of say 4. The decline in heterozygosity or rate of inbreeding at from the first generation would be: F1 = (1) / (2 * Ne) or 1 / (2 * 4) = .125.
With each subsequent generation the decline in heterozygosity is cumulative. Take generation F6
F6 = 1 - (1 - F1) ^ 6 = 1 - (1 - .125) ^ 6 = .551
By the 6th generation 55% of the genetic diversity will have been lost in the line. By the 12th generation 1 - (.87.5) ^ 12 = 80 % of the genetic diversity will have been eliminated.
The larger the Ne the lower the rate is the actual loss of diversity through inbreeding.
The actual calculation is fairly simple arithmetic and goes as follows:
Ne = 4 * (# of Males) * (# of Females) / (# of Males) + (# of Females)
For example a grower selects 1 male and 500 females for breeding. The effective breeding population is; (4) * (1) * (500) / (500+1) = 4. The effective breeding population can never be larger than the number of males selected for breeding. Another example 50 males 10 females Ne becomes 2000/60 or 33.33.
I read the article by DJ Short regarding his breeding of the famous Blueberry wherein he states that he only uses one male for his breeding selections. That might help explain why Blueberry is so resistant to breeding improvement. To quote, "Second, I select only one male from any single breeding project. Again, this simplifies things and avoids mistakes enormously. That male is generally selected at about the third week in the flowering cycle, unless it is a clone from another project".
By and large most cannabis breeders tend to ignore matters like effective breeding population when making their selections for males.
To expand on the basic concept of Ne one must consider how Ne effects the F statistic (Coefficient of Inbreeding).
So let's assume an NE of say 4. The decline in heterozygosity or rate of inbreeding at from the first generation would be: F1 = (1) / (2 * Ne) or 1 / (2 * 4) = .125.
With each subsequent generation the decline in heterozygosity is cumulative. Take generation F6
F6 = 1 - (1 - F1) ^ 6 = 1 - (1 - .125) ^ 6 = .551
By the 6th generation 55% of the genetic diversity will have been lost in the line. By the 12th generation 1 - (.87.5) ^ 12 = 80 % of the genetic diversity will have been eliminated.
The larger the Ne the lower the rate is the actual loss of diversity through inbreeding.