The figure below is a pedigree that shows the inheritance of a trait, Trait G, in a family

The figure below is a pedigree that shows the inheritance of a trait, Trait G, in a family. The presence of Trait G in an individual is determined entirely by Gene G. Gene G has 2 alleles: G, which is dominant, and g, which is recessive.

Each individual represented in the pedigree was assigned a number (shown below the symbol for the individual) for reference. Scientists determined that the Gene G genotype of Individual 20 is gg and that the Gene G genotype of Individual 21 is Gg. Based on this information, the scientists concluded that Trait G is a recessive trait.

1. How many generations are shown in the figure?

A. 3
B. 4
C. 22
D. 24

2. Based on the figure, the 2 individuals in which of the following pairs most likely have the greatest genetic similarity across their genomes?

F. Individual 3 and Individual 4
G. Individual 12 and Individual 13
H. Individual 16 and Individual 24
J. Individual 18 and Individual 21

3. Suppose that Individual 23 and Individual 24 have 4 biological children. Based on the figure, how many of the children, if any, have Trait G ?

A. 0
B. 1
C. 3
D. 4

4. According to the figure, how many of the grandchildren of Individual 1 and Individual 2, if any, have Trait G ?

F. 0
G. 1
H. 2
J. 7

5. Based on the figure, is it likely that Trait G is a sex-linked trait?

A. Yes, because mothers with Trait G always passed Trait G to their sons.
B. Yes, because mothers with Trait G did not always pass Trait G to their sons.
C. No, because mothers with Trait G always passed Trait G to their sons.
D. No, because mothers with Trait G did not always pass Trait G to their sons.

6. Based on the information provided, will an individual with the Gene G genotype Gg have Trait G ?

F. Yes, because Trait G is a dominant trait.
G. Yes, because Trait G is a recessive trait.
H. No, because Trait G is a dominant trait.
J. No, because Trait G is a recessive trait.

Answers

1. The best answer is B. The figure shows the first generation (Individuals 1 and 2), the second generation (Individuals 4, 6, and 7), the third generation (Individuals 10, 11, 12, 13, 15, 16, and 17), and the fourth generation (Individuals 18-23).

2. The best answer is G. In order to answer this item, the examinee must know that the more closely related two individuals are to each other, the greater the genetic similarity is likely to be. According to the figure, Individuals 12 and 13 are sisters and would likely have the greatest genetic similarity.

3. The best answer is D. In order to answer this item, the examinee must know how to work a genetic cross. According to the figure, both Individuals 23 and 24 have Trait G. According to the passage, Trait G is recessive. It follows that Individuals 23 and 24 both have the gg genotype and that all their children will also have the gg genotype. All their children will therefore have Trait G.

4. The best answer is H. According to the figure, the grandchildren of Individuals 1 and 2 are Individuals 10, 11, 12, 13, 15, 16, and 17. According to the key for the figure, a black circle and black square represent individuals with Trait G. Of the grandchildren, only Individuals 10 and 16 have Trait G.

5. The best answer is D. In order to answer this item, the examinee should know that with a sex-linked trait, an affected female passes the trait to all her sons. According to the figure, Individuals 4 and 10 were the only females with Trait G who had a son. Individual 4’s son, Individual 11, did not have Trait G. It follows that Trait G is not a sex-linked trait.

6. The best answer is J. According to the passage, Individual 21 has the Gene G genotype Gg. According to the figure, Individual 21 does not have Trait G. The passage states that Trait G is the recessive trait. An individual with the Gg genotype will have the dominant trait. F and G are incorrect; an individual with the Gg genotype will not have Trait G.