# Odds of genetic trait inheritance using probability?

1. Apr 30, 2012

### itlivesthere

I'd like to find out a way to predict how dominant a particular trait would be over the course of a particular number of generations. There will be only two traits going head to head, each with a particular probability of outcome.

Let's say the probability that Trait A will display as the phenotype of the population's offspring would be 50.1% (501 per 1000 births).
Let's say the probability that Trait B will display as the phenotype of the population's offspring would be 49.9% (499 per 1000 births).
The estimated total fertility rate is 2.36 children per woman.

I understand that many more variables would be needed for accurate figures, but I'm more interested in a general result to begin with.

Over the course of 8,000 generations of offspring and a constant fertility rate of 2.36, which percentage of the population would display the phenotype of Trait A or of Trait B?

(Note: I've tried binary logistic regression and even monohybrid crossing, but I seem to be screwing it up somehow.)

2. Apr 30, 2012

### SW VandeCarr

It's not clear what kind of genetics you're describing. In classical Mendelian genetics the phenotypes resulting from various combinations of dominant (D) and recessive traits (R) will be:

DD=D, DR=D, RD=D, RR=R. Thus the recessive phenotype will appear in 1/4 of the first generation on average.

Where did you get the distribution you described?

EDIT: If you have codominance with 2 alleles, then the Hardy-Weinberg equilibrium should hold between heterozygous (pq) and homozygous (p or q) offspring: That is p + q = 1 and $p^2 + 2pq + q^2 = 1$. Why couldn't you just plug your frequencies into this?

Last edited: May 1, 2012
3. May 1, 2012

### SW VandeCarr

Correction to the first equation which should be $(p+q)^2 = 1$.