Questions 15 to 17 refer to the following data: Snuffleups are small, ant eating
ID: 278398 • Letter: Q
Question
Questions 15 to 17 refer to the following data: Snuffleups are small, ant eating mammals that live deep in the jungles of Brazil. They possess a nose that varies between 3 inches long and 19 inches long. The exact length of the nose is determined by quantitative loci. If one crosses a 19 inch nosed snuffleup with one that has a 3 inch nose, one gets F1 offspring with 11 inch noses. When one crosses two F1 individuals, one gets an array of nose lengths from 3 to 19 inches long. However, among the F2, three inch noses occur only about 1 in 256 offspring, and 19 inch noses occur about one in 256 offspring.
15. How many loci are involved in forming this trait? a. 1 b. 2 c. 3 d. 4 e. 5 f. 6
16. What is the contribution per allele for this trait (in inches/allele)? a. 6 b. 5 c. 4 d. 3 e. 2 f. 1
17. Two 11 inch nosed F1 individuals are crossed. How often will their progeny have noses 9 inches long? a. 8/256 b. 1/256 c. 28/256 d. 56/256 e. 70/256
Explanation / Answer
15. Option D is correct
Four genes are involved in the determination of the nose length.
It is clear that 1/256 is completely homozygous recessive (shortest nose length) and 1/256 is completely homozygous dominant (longest nose length). From this, we can say that there are four loci controlling this trait.
16. Option E is correct.
Parental cross: AABBCCDD (19 inches) X aabbccdd (3 inches)
F1 progeny: AaBbCcDd (11 inches)
Background (default) nose length when all the alleles are recessive = 3 inches
Nose length in F1 with 4 dominant alleles = 11 inches
Length difference = 11 - 3 = 8 inches
Contribution from each allele = 8/4 = 2 inches
17. Option D is correct
9 inches nose = 3 dominant alleles
EX: AABbccdd, AaBbCcdd etc..
The probability is 56/256
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