Download Answers to End-of-Chapter Questions – Brooker et al ARIS site

Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 16
Test Yourself Questions
1. Based on Mendel’s experimental crosses, what is the expected F 2 phenotypic ratio of a monohybrid
cross?
a. 1:2:1
b. 2:1
c. 3:1
d. 9:3:3:1
e. 4:1
Answer: c. The F2 generation is the result of crossing F1 individuals, which are heterozygous. When two
heterozygous individuals are crossed the results would be ¾ of the offspring express the dominant
phenotype and ¼ of the offspring would express the recessive phenotype.
2. During which phase of cellular division does Mendel’s law of segregation physically occur?
a. mitosis
b. meiosis I
c. meiosis II
d. all of the above
e. b and c only
Answer: b. Mendel’s law of segregation refers to the separation of the two alleles into separate cells.
Meiosis is the cellular division process that produces haploid cells. During the first meiotic division, a
diploid cell divides to produce haploid cells. This is the phase in which the two alleles segregate, or
separate, from each other.
3. An individual that has two different alleles of a particular gene is said to be
a. dihybrid.
b. recessive.
c. homozygous.
d. heterozygous.
e. hemizygous.
Answer: d. An individual that is heterozygous has two different alleles of a particular gene (e.g., Aa).
4. Which of Mendel’s laws cannot be observed in a monohybrid cross?
a. segregation
b. dominance/recessiveness
c. independent assortment
d. codominance
e. All of the above can be observed in a monohybrid cross.
Answer: c. Independent assortment describes how pairs of alleles segregate independently of each
other. This requires the observation of two or more pairs of alleles.
5. During a ____ cross, an individual with the dominant phenotype and unknown genotype is crossed
with a ______ individual to determine the unknown genotype.
a. monohybrid, homozygous recessive
b. dihybrid, heterozygous
c. test, homozygous dominant
d. monohybrid, homozygous dominant
e. test, homozygous recessive
Answer: e. A testcross is used to determine the genotype of an individual with the dominant phenotype.
In a test cross, an individual that exhibits the recessive phenotype, and is therefore homozygous
recessive, is crossed with the unknown. The ratio of the offspring phenotypes will be used to determine
the genotype of the unknown.
6. In humans, males are said to be ______ at X-linked loci.
a. dominant
b. homozygous
c. recessive
d. heterozygous
e. hemizygous
Answer: e. Because males carry only one copy of X-linked genes, they are said to be hemizygous.
7. A gene that affects more than one phenotypic trait is said to be
a. dominant.
b. wild type.
c. dihybrid.
d. pleiotropic.
e. heterozygous.
Answer: d. Pleiotropy refers to the phenomenon where one gene affects more than one phenotypic trait.
8. A hypothetical flowering plant species produces red, pink and white flowers. To determine the
inheritance pattern, the following crosses conducted with the results indicated:
red x red  all red
white x white  all white
red x white  all pink
What type of inheritance pattern does this represent?
a. dominance/recessiveness
b. X-linked
c. codominance
d. incomplete dominance
e. pleiotropy
Answer: d. Incomplete dominance refers to the inheritance pattern where the heterozygous expresses a
phenotype that is intermediate to the homozygotes.
9. Genes located on a sex chromosome are said to be ____________.
a. X-linked.
b. dominance.
c. hemizygous.
d. sex-linked .
e. sex-influenced.
Answer: d. Sex-linked refers to genes located on the sex chromosomes, either X or Y for example.
Genes located specifically on the X chromosome are X-linked.
10. Genes that are expressed differently depending on whether the individual is male or female are
a. sex-linked
b. pleiotropic
c. sex-influenced
d. incomplete dominant
e. hemizygous
Answer: c. Sex-influenced genes refer to genes that are autosomal but are expressed differently in
males than in females.
Conceptual Questions
1. Define genotype and phenotype.
genotype: The genetic composition of an individual.
phenotype: The characteristics of an organism that are the result of the expression of its genes.
2. Define autosome.
autosomes: The paired chromosomes.
3. Explain why recessive X-linked traits in humans are more likely to occur in males.
Answer: Because males are hemizygous, they may display a recessive trait that is masked by the
dominant allele in a heterozygous female. It only takes one recessive allele for the male to display the
trait.
Experimental Questions
1. Prior to the Feature Investigation, what was the original purpose of Morgan’s experiments with
Drosophila?
Answer: Morgan was testing the hypothesis of use and disuse. This hypothesis suggests that if a
structure is not used, over time, it will diminish and/or disappear. In Morgan’s experiments, originally he
was testing to see if flies reared in the dark would lose some level of eye development.
2. How was Morgan able to demonstrate red-eye color is dominant to white-eye color?
Answer: Using the same methods as Mendel, Morgan crossed a true-breeding strain of red-eye flies
with a white-eyed fly. All of the offspring were red-eye indicating that red-eye was the dominant trait.
3. What results led Morgan to conclude that eye color was associated with the sex of the individual?
Answer: When the F1 individuals were crossed, the ratio was slightly different than the expected
Mendelian ratio. Only male F2 offspring expressed the white-eye color. At this time, Morgan was aware
of sex chromosome differences between male and female flies. He realized that since males only
possess one copy of X-linked genes, this would explain why only F2 males exhibited the recessive trait.
Collaborative Questions
1. Discuss Mendel’s two laws and why they are important.
Answer:
The law of segregation - This law states that the two copies of a gene (alleles) segregate from each
other during transmission from parent to offspring. In other words, for each pair of alleles your mother
will give you only one and your father will give you only one. This will give you a total of two alleles per
trait. The impact of this law is that in each generation there is a shuffling of genes to get a unique
individual.
Independent assortment - This law states that the alleles of each different gene assort randomly during
gamete formation. In other words a specific allele for one gene may be found in a gamete regardless of
which allele for a different gene is found in the same gamete. This also shuffles the genes and
increases the genetic diversity of a species.
2. What are the fundamental principles of the chromosome theory of inheritance?
Answer:
a. Chromosomes contain the genetic information that is passed from parent to offspring and from one
cell to another. Genes, the basic units of genetics, are found on these chromosomes.
b. Chromosomes are replicated and each chromosome retains its individuality (the same number and
type of genes) during cell division and gamete formation.
c. The nucleus of a diploid cell contains two sets of chromosomes that are found in homologous pairs.
Half of these chromosomes come from the mother and the other half comes from the father and each
set of chromosomes carry a full complement of genes.
d. During meiosis, one member of each chromosome pair segregates into one daughter nucleus and its
homologue segregates into the other daughter nucleus. Each of the resulting haploid cells contain only
one set of chromosomes. During the formation of haploid cells, the members of different chromosome
pairs segregate independently of each other.
e. Gametes are haploid cells that combine to form diploid cells during fertilization, with each gamete
transmitting one set of chromosomes to the offspring.