Question

Suppose a graduate student is studying a population of bluebonnets along a roadside. The plants in this population are genetically variable. She counts the seeds produced by 100 plants and measures the mean and variance of seed number. The variance is 30. Selecting one plant, the student takes cuttings from it and cultivates them, producing many genetically identical clones. She then transplants these clones into the roadside population, allows them to grow for one year, and then counts the number of seeds produced. The student finds that the variance in seed number among the cloned plants is 10.

From the phenotypic variance (??)of the genetically variable and genetically identical plants, calculate the broad‑sense heritability (?2) of seed number for the roadside population of bluebonnets.

?2=???????????

Choose which assumption must be made in order for this estimate of broad-sense heritability to be correct.

1. The genetic variance component is strictly the result of additive genetic variance.

2. The phenotypic variance of the genetically identical plants is the same as the genetically variable population.

3. There is no phenotypic variance associated with the environment.

4. The environmental variance of the genetically identical plants is the same as that of the genetically variable population.

Suppose a farmer is interested in developing a breeding program on his chicken farm. The farmer would like to artificially select for egg weight, egg shape, shell color, and shell thickness. In a large population of his chickens, the farmer has measured these four continuous egg traits of interest and calculated their variances, which are shown in the table.

Variance	Weight	Shape	Shell Color	Shell thickness
Phenotypic	503	1043	112	526
Additive Genetic	12	140	59	15
Environmental	250	522	53	220
Dominance genetic	16	657	11	23

Which trait would best respond to artificial selection by the farmer?

1. shell color

2. egg shape

3. shell thickness

4. egg weight

Select all of the statements that identify how the farmer might utilize the information gained from his data.

-Further inbreed the chickens on the farm with the largest egg weight to improve the overall phenotype.

-Identify quantitative trait loci correlated to each trait examined in the chicken population after obtaining genetic sequence data for his chicken population.

-Recommend a selective breeding program for a population of chickens from another country based on his results.

-Design an experiment to improve the weight trait in the current chicken population by changing the farm environment.

Answer 1

Answer to the first question:

Broad sense heritability (H²) is an estimation of effect of all genetic factors on phenotypic variations (V_p). Mathematically,

H² =V_G/V_P ----------(i)

Total phenotypic variation is a sum of variance due to genetic factors and variance due to environmental factors (V_E),

V_P=V_G + V_{E -------(ii)}

It is given that in 100 random plants, variance is 30. This is the total phenotypic variation or V_P.

Also, in the cloned plants all will be genetically same, and any difference would be due to environmental factors. Variance in cloned plants is 10, thus V_E = 10.

We have V_P=30 and V_E=10. Thus, from equation (ii),

V_G=30-10

V_G=20

Using the values of Vp and V_G in (i) we get,

Hence,  the broad‑sense heritability (?2) of seed number for the roadside population of bluebonnets is 2/3 or 0.67.

Answer 2:

Assumption that must be made in order for this estimate of broad-sense heritability to be correct:

The environmental variance of the genetically identical plants is the same as that of the genetically variable population.