A12 fiffAnswers
Figure 6.10
Q1: During meiosis, does random assortment occur before or after
crossing-over?
A1: A f ter.
Q2: What would be the effect on genetic diversity if homologous
chromosomes did not randomly separate into the daughter cells
during meiosis?
A2: Genetic diversity would decrease.
Q3: With two pairs of homologous chromosomes, four kinds of
gametes can be produced. How many kinds of gametes can be
produced with three pairs of homologous chromosomes? What
does this suggest for the 23 homologous pairs of chromosomes in
human cells?
A3: Three pairs of homologous chromosomes can produce eight
kinds of gametes. Therefore, 23 homologous pairs could produce
huge variation in gametes. To be more precise, it could produce
223 (8,388,608) different combinations of chromosomes in
gametes.
CHAPTER 7
END-OF-CHAPTER ANSWERS
- genotype: 4, phenotype: 5, heterozygote: 1, homozygote: 2,
dominant: 6, recessive: 3- gene, alleles
- meiosis, segregation, independent assortment
- (a) M, (b) C, (c) C, (d) C, (e) M
- e
- e
- incomplete dominance
- d
- pleiotropic
- b, c, e
- The first-generation result suggests that the round-shape
allele is dominant to the oval-shape allele. The next cross
should be to breed offspring with themselves to create an
F 2 generation, and the proportion of ovals would be 1 in 4,
or 25 percent (3:1 round to oval).- Orange color must be dominant to black color. You could
breed their offspring to test the hypothesis.- (a) llff (homozygous recessive for both long hair and no
furnishings)
( b) LlFf, LLFF, LlFF, LLFf
(c) 9:3:3:1 short furnished to short unfurnished to long
furnished to long unfurnished.ANSWERS TO FIGURE QUESTIONS
Figure 7.2
Q1: What is the physical structure of a gene?A1: A gene is a strand of DNA within a chromosome.Q2: How many copies of each gene are found in the diploid cells in
a woman’s body?A2: Tw o.Q3: With 46 chromosomes in a human diploid cell, how many
chromosomes come from the person’s mother and how many from
the father?A3: Each parent contributes half of the chromosomes, so
23 chromosomes from the mother and 23 from the father.Figure 7.3
Q1: Which might you observe directly: the genotype or the
phenotype?A1: The phenotype may be directly observable.Q2: Which poodle could be heterozygous: the one with the black
coat or the one with the brown coat?A2: Only the black-coated poodle may be heterozygous.Q3: Can you identify with certainty the genotype of a black
poodle? A brown poodle?A3: No for a black poodle; yes for a brown poodle.Figure 7.4
Q1: What would you predict about the color of the F 1 plants’
flowers?A1: They should all be purple.Q2: Why was it important that Mendel begin with pea plants that
he knew bred true for flower color? Why couldn’t he simply cross a
purple-flowered plant and a white-flowered plant?A2: The purple-flowered plant might be heterozygous or
homozygous.Q3: Over the years, Mendel experimented with more than 30,000 pea
plants. Why did Mendel collect data on so many plants? Why
didn’t he study just one cross? Hint: Read “What Are the Odds?”
on page 124 before answering.A3: With data from more plants, there is a better chance that the
results will accurately reflect reality.Figure 7.5
Q1: Why did Mendel’s entire F 1 generation look the same?A1: All of the F 1 plants were heterozygous, so they all had a purple
phenotype.Q2: The phenotype ratio in the F 2 generation is 3:1 purple-to-white
flowers. What is the genotype ratio?A2: 1:2:1.