In a herd of dairy cows the narrow-sense heritability for milk protein content is 0.76, and for milk butterfat it is 0.82. The correlation coefficient between milk protein content and butterfat is 0.91. If the farmer selects for cows producing more butterfat in their milk, what will be the most likely effect on milk protein content in the next generation?

In an assessment of learning in Drosophila, flies were trained to avoid certain olfactory cues. In one population, a mean of 8.5 trials was required. A subgroup of this parental population that was trained most quickly (mean=6.0) was interbred, and their progeny were examined. These flies demonstrated a mean training value of 7.5. Calculate realized heritability for olfactory learning in Drosophila.

Suppose you want to develop a population of Drosophila that would rapidly learn to avoid certain substances the flies could detect by smell. Based on the heritability estimate you obtained in Problem 16, do you think it would be worth doing this by artificial selection? Why or why not?

In a population of tomato plants, mean fruit weight is 60 g and h² is 0.3. Predict the mean weight of the progeny if tomato plants whose fruit averaged 80 g were selected from the original population and interbred.

What techniques can scientists use to determine if a particular transgene has been integrated into the genome of an organism?

In a population of 100 inbred, genotypically identical rice plants, variance for grain yield is 4.67. What is the heritability for yield? Would you advise a rice breeder to improve yield in this strain of rice plants by selection?

While most quantitative traits display continuous variation, there are others referred to as “threshold traits” that are distinguished by having a small number of discrete phenotypic classes. For example, Type 2 diabetes (adult-onset diabetes) is considered to be a polygenic trait, but demonstrates only two phenotypic classes: individuals who develop the disease and those who do not. Theorize how a threshold trait such as Type 2 diabetes may be under the control of many polygenes, but express a limited number of phenotypes.