Question

All cattle are part of the same species, Bos taurus. There are many different breeds of cattle. Herefords and Simmental are two different breeds of cattle.



A rancher raises a herd of Hereford cattle and a herd of Simmental cattle. All cattle have access to the same amount of food and space in the rancher's pasture. Each type of cattle consumes the same amount of calories of similar food each day. Both types of cattle reach maturity and adulthood when they are 1 year old. The table below compares the average weight of a newborn calf and the average weight of an adult cow in each of the rancher's herds.

Breed Calf Weight Adult Weight
Hereford 90 pounds 980 pounds
Simmental 90 pounds 1,050 pounds

Which of the following best explains the difference in growth between the two herds?
A.
Factors in the environment promote the growth of Simmental cattle more than the growth of Hereford cattle.
B.
Simmental cattle have genetic differences from Hereford cattle that result in higher rates of growth.
C.
The growth of Simmental cattle and Hereford cattle is controlled by completely different genes.
D.
Limited food and space reduce the growth of Simmental cattle more than the growth of Hereford cattle.

Answer 1

Answer: B.

Reason: Both herds experience the same environment, food, and starting weight, so environmental differences can't explain the heavier Simmental adults. Breed differences reflect inherited (genetic) variation in growth rate and adult size. Option C is too strong—breeds share most genes—while A and D conflict with the stated equal conditions.