Download CHAPTER 7

CHAPTER 7
Concept check questions (in figure legends)
FIGURE 7.1
Concept check: Which types of offspring are found in excess based on Mendel’s law of
independent assortment?
Answer: The offspring found in excess are those with purple flowers, long pollen, and red
flowers, round pollen.
FIGURE 7.2
Concept check: If a crossover began in the short region between gene A and the tip of the
chromosome, would this event affect the arrangement of the A and B alleles?
Answer: No, such a crossover would not change the arrangements of these alleles.
FIGURE 7.3
Concept check: Of the 8 possible phenotypic combinations in the F2 generation, which ones
are the product of a single crossover?
Answer: A single crossover can produce offspring with: gray body, red eyes, miniature
wings; gray body, white eyes, miniature wings; yellow body, red eyes, long wings; and
yellow body, white eyes, long wings.
FIGURE 7.4
Concept check: Why are the parental offspring more common than the recombinant
offspring?
Answer: When genes are relatively close together, a crossover is relatively unlikely to
occur between them. Therefore, the parental offspring are more common.
FIGURE 7.5
Concept check: Why are the types of offspring described in panel (b) more numerous than
those described in panel (c)?
Answer: The reason is because the w and m genes are farther apart than the y and w genes.
FIGURE 7.6
Concept check: In this experiment, what are the two types of characteristics that crossing
over can change? Hint: one type is seen only with a microscope whereas the other type can
be seen with the unaided eye.
Answer: Crossing over can change the combination kernel phenotypes and also it can
change the morphologies of the chromosomes compared to the parental chromosomes.
FIGURE 7.7
Concept check: List 5 reasons why genetic maps are useful?
Answer: Genetic mapping is useful to: (1) understand the complexity and genetic
organization of a species; (2) understand the underlying basis of inherited traits; (3) clone
genes; (4) understand evolution; (5) diagnose and treat diseases: (6) predict the likelihood
of a couple having offspring with genetic diseases; (7) agricultural breeders of livestock
and crops.
FIGURE 7.8
Concept check: When and in which fly or flies did crossing over occur in order to produce
the recombinant offspring?
Answer: Crossing over occurred during oogenesis in the female parent of the recombinant
offspring.
FIGURE 7.9
Concept check: Describe the basic strategy that is followed in this experiment.
Answer: The basic strategy is to conduct testcrosses, like the one shown in Figure 7.8. The
percentage of recombinant offspring is a measure of the map distance between the genes.
FIGURE 7.10
Concept check: What phenomenon explains why the maximum percentage of recombinant
offspring does not exceed 50%?
Answer: Multiple crossovers prevent the maximum percentage of recombinant offspring
from exceeding 50%.
FIGURE 7.11
Concept check: Does mitotic recombination occur in a gamete (sperm or egg cell) or in a
somatic cell?
Answer: Mitotic recombination occurs in somatic cells.