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SEC T I O N 9 - 1 R E VIEW
M ENDEL’S L EGACY
VOCABULARY REVIEW Distinguish between the terms in each of the following pairs
of terms.
1. F1 generation, F2 generation
2. dominant, recessive
3. self-pollination, cross-pollination
MULTIPLE CHOICE Write the correct letter in the blank.
1. Mendel obtained plants that were true-breeding for particular traits by
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a. growing plants from the seeds of
other plants that showed that trait.
b. discarding plants that showed
other traits.
c. allowing plants to self-pollinate for several
generations.
d. allowing plants to cross-pollinate for
one generation.
2. When Mendel crossed a strain of tall pea plants with a strain of short pea plants, he
observed that all of the plants in the F1 generation were tall. This suggests that
a. the tall trait was controlled by a
dominant factor.
b. the short trait was controlled by
a dominant factor.
c. both traits were controlled by a
recessive factor.
d. the strain of short plants was not capable of pollinating the strain of tall plants.
3. A cross between true-breeding green-podded pea plants and true-breeding yellow-podded
pea plants produces only green-podded plants. When the F1 generation is allowed to selfpollinate, the F2 generation consists of
a.
b.
c.
d.
only green-podded plants.
only yellow-podded plants.
about three-quarters yellow-podded plants and one-quarter green-podded plants.
about three-quarters green-podded plants and one-quarter yellow-podded plants.
4. When alleles for different characteristics are on separate chromosomes, they are
distributed to gametes independently. This observation is summarized by the law of
a. cross-pollination.
b. independent assortment.
c. segregation.
d. molecular genetics.
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SHORT ANSWER Answer the questions in the space provided.
1. What does the term allele mean as it is used in genetic crosses?
2. Explain how the events of meiosis account for the law of segregation and the law of independent
assortment.
3. If orange flower color in a plant is controlled by an allele F and red flower color is controlled by
an allele f, which flower color is dominant?
If true-breeding orange-flowered plants are crossed with true-breeding red-flowered plants, what
will be the flower color(s) of the F1 plants?
4. Critical Thinking How would Mendel’s observations and conclusions have been different if
many of the characteristics he studied, such as seed color and seed texture, had been controlled
by genes located close together on the same chromosome?
The diagram below shows the assortment of two pairs of homologous chromosomes during
meiosis. One pair has a gene for flower color (R allele = red, r allele = white). The other pair has a
gene for seed color (B allele = brown, b allele = gray).
REPRODUCTIVE CELL
R
GAMETES
46
Section 9-1 Review
r B
b
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STRUCTURES AND FUNCTIONS In the spaces inside each gamete, indicate the four possible combinations of alleles the gametes could receive.
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SEC T I O N 9 - 2 R E VIEW
G ENETIC C ROSSES
VOCABULARY REVIEW Define the following terms, and provide one example for each.
1. complete dominance
2. incomplete dominance
3. codominance
MULTIPLE CHOICE Write the correct letter in the blank.
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1. The appearance of an organism is its
a. genotype.
b. phenotype.
c. genotypic ratio.
d. phenotypic ratio.
2. A genetic cross performed many times produces 798 long-stemmed plants and 266 shortstemmed plants. The probability of obtaining a short-stemmed plant in a similar cross is
a. 266/1,064.
b. 266/798.
c. 798/266.
d. 798/1,064.
3. A monohybrid cross of two individuals that are heterozygous for a trait exhibiting
complete dominance would probably result in a phenotypic ratio of
a. 4 dominant:0 recessive.
b. 1 dominant:3 recessive.
c. 3 dominant:1 recessive.
d. 1 dominant:1 recessive.
4. To determine the genotype of an individual that shows the dominant phenotype, you
would cross that individual with one that is
a. heterozygous dominant.
b. heterozygous recessive.
c. homozygous dominant.
d. homozygous recessive.
5. In a dihybrid cross between an individual with the genotype RRYY and an individual with
the genotype rryy, all of the offspring will have the genotype
a. RRYY.
b. RrYY.
c. RrYy.
d. rryy.
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SHORT ANSWER Answer the questions in the space provided.
1. What is the difference between a homozygous individual and a heterozygous individual?
2. If the probability that a specific trait will appear in the F2 generation is 0.25, how many individuals would be expected to show that trait in an F2 generation consisting of 80 individuals?
3. A homozygous dominant individual (AA) is crossed with an individual that is heterozygous for
the same trait (Aa). What are the possible genotypes of the offspring, and what percentage of the
offspring is likely to show the dominant phenotype?
4. Critical Thinking Some animals, such as cows, normally produce only one offspring from each
mating. If a cow showed a dominant phenotype, why would a typical testcross be a difficult way
to determine the genotype of that animal?
STRUCTURES AND FUNCTIONS Write the possible genotypes of the offspring in the
Punnett square below. Then answer the questions in the spaces provided.
WwRr
1. What proportion of the offspring will
be dominant for both traits?
2. What proportion of the offspring
will have the same genotype as
their parents?
3. What proportion of the offspring will be
homozygous dominant for both traits?
WwRr
4. What proportion of the offspring will be
homozygous recessive for both traits?
48
Section 9-2 Review
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A plant with the genotype WwRr is crossed with another plant with the same genotype.
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3. Vesicles formed by the Golgi apparatus fuse at
the midline of the cell to form the cell plate, a
cell wall that elongates to separate the cell into
two cells.
4. Without a G1 growth phase, the cells would not
grow to their mature size after cytokinesis.
Therefore, the offspring cells would become
smaller with each cell cycle.
STRUCTURES AND FUNCTIONS
a, telophase; b, metaphase; c, prophase; d, anaphase
Section 8-3
VOCABULARY REVIEW
1. Oogenesis is the production of mature egg cells,
or ova.
2. A tetrad is a pair of homologous chromosomes lined
up next to each other during prophase I of meiosis.
3. Independent assortment is the random separation
of homologous chromosomes during anaphase I.
4. Polar bodies are haploid offspring cells produced
by meiosis during oogenesis.
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MULTIPLE CHOICE
1. d
2. c
3. a
4. b
5. c
SHORT ANSWER
1. Genetic recombination occurs during crossingover and independent assortment.
2. Prophase I: DNA coils into chromosomes, the nucleolus and nuclear envelope disappear, the mitotic
spindle forms, and synapsis and crossing-over occur.
Metaphase I: the tetrads line up randomly along the
midline of the cell, and spindle fibers attach to the
centromere of each homologue. Anaphase I: the
homologues move toward opposite poles of the cell.
Telophase I: the chromosomes reach the opposite
ends of the cell, and cytokinesis begins.
3. In meiosis I, the offspring cells are haploid but
each cell contains two copies of the chromosome
because the original cell copied its DNA before
meiosis I. The offspring cells of meiosis II are also
haploid, but each cell contains only one copy of
the chromosome because, unlike meiosis I, the
cells do not copy their DNA before meiosis II.
4. The advantage of asexual reproduction is that offspring are genetically identical to their parent, so if
the parent is well adapted to its environment, the
offspring will also be well adapted. The disadvantage of asexual reproduction is that without genetic
recombination, the offspring lack the variability that
would allow some to survive if the environment
became less favorable to their survival.
STRUCTURES AND FUNCTIONS
a, anaphase II; b, metaphase I; c, anaphase I;
d, metaphase II
Section 9-1
VOCABULARY REVIEW
1. The F1 generation consists of the offspring of a
cross between two parents; the F2 generation consists of the offspring of a cross between two individuals in the same F1 generation.
2. A dominant factor is one that masks the effect of
another factor for the same characteristic; a recessive factor is one whose effect is masked by another factor for the same characteristic.
3. Self-pollination occurs between flowers on the same
plant. Cross-pollination occurs between flowers on
different plants.
MULTIPLE CHOICE
1. c
2. a
3. d
4. b
SHORT ANSWER
1. An allele is each of two alternative forms of a
gene.
2. In meiosis, the two alleles of each gene are segregated when the two chromosomes in each pair of
homologues are separated into different gametes.
Alleles of genes located on different chromosomes
or far apart on the same chromosome assort independently when homologues are randomly separated during meiosis.
3. Orange flower color is dominant. All of the F1
plants will have orange flowers.
4. Mendel would have observed that the traits
controlled by dominant factors for these characteristics almost always appeared together. Thus, he
might not have concluded that the factors for different characteristics are assorted independently.
STRUCTURES AND FUNCTIONS
Possible combinations are RB, Rb, rB, and rb.
Section 9-2
VOCABULARY REVIEW
1. In complete dominance, heterozygous and dominant homozygous individuals have the same phenotype. For example, in pea plants, the P allele is
completely dominant over the p allele, so both PP
and Pp plants have purple flowers.
2. In incomplete dominance, neither allele is completely dominant over the other and both influence the phenotype. For example, in four o’clocks,
neither the R nor r allele is completely dominant,
so Rr plants have pink flowers.
3. In codominance, neither allele is dominant or
recessive; both are expressed in heterozygotes.
For example, in MN blood blood types, both M and
N molecules are produced by an LMLN individual.
MULTIPLE CHOICE
1. b
2. a
3. c
4. d
5. c
SHORT ANSWER
1. In a homozygous individual, both alleles of a pair
are the same; in a heterozygous individual, the
two alleles of a pair are different.
2. 0.25 × 80 individuals = 20 individuals
3. AA and Aa will result. 100% will have the dominant
phenotype.
4. In a testcross, the dominant phenotype would
appear in all of the offspring if the cow were
homozygous dominant but in only about 50% of
the offspring if the cow were heterozygous. With
only one individual per F1 generation, distinguishing between these two possibilities would
take a long time, until a calf with the recessive
phenotype was born.
STRUCTURES AND FUNCTIONS
Arrangements of the offspring alleles will vary
according to the order of the parental alleles in the
Punnett square. 1. 9/16 2. 1/4 3. 1/16 4. 1/16
Modern Biology Study Guide Answer Key
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