Question

14.    Evolutionary change of a trait in a population under the effect of selection can occur only when

         a) VE > 0 b) h2 > 0 c) h2 = 0 d) VE = 0

15.    You examine body weight in a laboratory population of mice. You find that individuals fall into five discrete weight classes with mean weights of 15 grams, 20 gr., 25 gr., 30 gr., and 35 gr. The variance of weight within each class is very low, and the distribution of weights in the different weight classes do not overlap. Based on these observations you would conclude that in this population and environment

a) body weight is a quantitative trait b) body weight is a qualitative trait   c) body weight is affected by many different genes d) body weight is affected only by environment e) a & d.

16.    In sage plants, height is affected by only one gene, T. One hundred seeds of genotype TT are grown in a field. After one month the plants are measured and are found to exhibit a continuous normal distribution of heights ranging from 4 to 12 inches. What can you conclude about this phenotypic variation? a) it must be due to genetic variation alone b) it must be due to environmental variation alone c) it is due to a combination of genetic and environmental variation d) you cannot tell the source of the variation.

17.    You bring a sample of flies from a natural population into the laboratory and begin selecting for high body weight by using the heaviest 20% of the population as parents each generation for five generations. If mean body weight remains the same in each generation

         a) phenotypic variation is due only to effects of the environment b) phenotypic variation is due only to genetic variation among individuals c) VG > 0 d) VE = 0

18.    Given the observations described in the previous question you would conclude that for body weight

         a) heritability is zero b) heritability is greater than zero but less than 1 c) heritability is 1 d) heritability is greater than 1

19.    The heritability of body weight in cows a) can be measured on a single individual b) is the proportion of VG which is due to VE  c) is the proportion of VP which is due to VG   d) is the proportion of VE transmitted to offspring e) all of the above.

Answer 1

14. Change in a trait has nothing to do with heritability. Heritability only talks about the probabilistic tendency of a trait in being inherited. However, The environment plays a major role in modifying a trait or to direct the inheritance of a trait in a given condition. The answer is Option a. Variability due to environment is more than Zero (VE>0).

15. Since the variance of weights in each weight classes is low, but also the distribution of weights in the weight classes do not overlap there are two factors that play a role. The low variation of weights is possible when this trait is quantitative. However, the weight value still do not overlap with each other so , the environment plays a major role too to induce some variation. The answer is Option e.

16. The Sage plant is homozygous dominant. So no variable genetic components can be in play to alter the height of the plants. The difference is environmental in nature. The answer is Option b.

17. Sice the mean body weight of the flies remains the same in the successive generations, the inheritance of weight is not a genetic phenomenon but environmental. So the answer is Option a.

18. Since body weight is environmental, the heritability is zero. Hence Option a is the answer.

19. Actually heritability is calculated by the ratio of Genetic Variability(VG)/ Total Variability(VP).
No option is correct.