1) Two alleles expressing exactly the same information for a trait are designated as ________.
2) Dominant alleles are so called because under most circumstances they ________.
A) code only for tallness and dark skin
B) suppress the expression of other alleles
C) code for genes that are never considered lethal
D) code for most phenotypic and genotypic expressions of a trait
3) Recessive genes are usually expressed in humans only when ________.
A) they are coding for skin color
B) they are coding for genetic diseases
C) the organism is in the embryonic stage
D) both alleles are exactly the same, or homozygous
4) Those characteristics that can be determined on superficial inspection of an individual are
known as ________.
5) The number of gamete types from independent assortment of the homologues during meiosis
in humans would be:
A) 21 × 2 (42)
B) 232 (529)
C) 223 (78 million)
D) 46 × 2 (92)
6) A female infant is born with several hundred oocytes, each one genetically unique. This is due
B) recessive inheritance
C) chromosome deletion
D) independent assortment and random crossover
7) If we are to consider the variation resulting only from independent assortment and random
fertilization, any resulting offspring represents about one out of ________.
A) 64 zygotes possible
B) 23,000 zygotes possible
C) 64,000 zygotes possible
D) 72 trillion zygotes possible
8) Mitosis differs from meiosis because in meiosis we observe ________.
9) The reason recessive genetic disorders are more frequent than disorders inherited as dominant
is that ________.
A) dominant genetic disorders are never expressed in males
B) people carrying dominant genetic disorders always die before birth
C) carriers may pass them on to their offspring, unaware that they are carriers
D) recessive genetic disorders are limited to persons of the same ethnicity
10) The gene responsible for the condition known as sickle-cell anemia demonstrates ________.
A) incomplete dominance
B) a dominant genetic disorder
C) a sex-linked genetic disorder
D) a recessive genetic disorder
11) An example of multiple allele inheritance is ________.
A) the ABO blood group
B) the appearance of freckles on the skin
C) the appearance of birthmarks on the skin
D) hair that seems to have several shades of a color
12) Which of the following is true concerning environmental influence on genetic expression?
A) It is impossible to alter in any way the expression of a gene in humans.
B) The only time a gene can be influenced by environmental factors is in the second
trimester of the pregnancy.
C) Environmental factors determine the way in which 90 percent of our genes are
D) Drugs and nutrition can alter normal gene expression.
13) Sex chromosomes of a normal male are ________.
D) Any of these, depending on the father
14) A woman has blond hair and brown eyes. This statement is best described as indicating
A) allelic pairs
B) recessive traits
15) A chromosomal aberration in which part of a chromosome is lost is known as ________.
D) crossing over
16) Inheritance of stature (height) in humans is probably due to ________.
C) incomplete dominance
D) polygene inheritance
17) Huntingtonʹs disease is an example of a(n) ________ gene.
D) incomplete dominant
18) An individual who is heterozygous for a particular trait, yet expresses both alleles of that trait,
is an example of ________.
B) recessive inheritance
C) incomplete dominance
D) sex-linked inheritance
20) Given the information in Figure 29.1, what would the genotype ratio be for the offspring?
21) Given the information in Figure 29.1, what is the phenotype ratio (assuming C is dominant
and there is no incomplete dominance)?
22) Given the information in Figure 29.1, if C were an incomplete dominant trait, what would the
phenotype ratio be for the offspring?
23) ________ is the most common type of fetal testing.
A) Blood chemistry
C) A DNA probe
24) Huntingtonʹs disease involves ________.
A) hypersecretion of growth hormone
B) the presence of an extra chromosome
C) degeneration of the basal nuclei of the brain
D) hyposecretion of thyroxine
25) One possible scientific explanation for siblings having very different skin color is ________.
A) polygene inheritance, which results in continuous phenotypic variation between
B) that some people may be in the sun longer than others
C) that the gene for dark skin is dominant over the gene for light skin, and some offspring
inherit chromosomes with one of each allele
D) There is no explanation for the variation
26) Which of the following statements is true concerning screening?
A) Screening is illegal in over half of the world.
B) Screening can be done only in the first trimester of pregnancy.
C) Genetic screening is rarely done because it yields very little accurate information.
D) Screening can be done before conception by carrier recognition or during fetal testing.
27) The diploid genome contains chromosomes from ________.
A) the father only
B) the mother only
C) each parent, and it synthesizes others
D) both the mother and father, but only about half of the genome from each
28) Amyʹs hand was exposed to X rays. A gene in a skin cell of her hand mutated. This mutant
A) will definitely cause skin cancer
B) will replicate itself and be passed on to Amyʹs children
C) will not form an exact duplicate of itself when the cell divides
D) will replicate itself when the cell divides but will not be passed on to Amyʹs offspring
29) Select the incorrect statement about Chromosomes and genes.
A) Genes on neighboring but different chromosomes are called linked.
B) Recombinant chromosomes have segments of DNA from each parent on the same
C) The longer a chromosome, the more crossovers are expected.
D) A personʹs genetic makeup is referred to as his or her genotype.
30) The main way a recessive allele would be expressed even when only one copy is present
would be ________.
B) recessive inheritance
C) sex-linked inheritance
D) incomplete dominance
31) A couple whose blood types are A (IAi) and B (IBi) may have a child with which of the
following blood types?
A) AB only
B) A and B only
C) A, B, AB, and O
D) AB and O only
32) Gene mutations in the sex chromosomes of the human would tend to become visibly
A) more frequently in males
B) more frequently in females
C) equally frequently in both sexes
D) in neither males or females
33) For which of the following are newborn infants not routinely screened at birth?
B) color blindness
C) imperforate anus
D) congenital hip dysplasia
Fill-in-the-Blank/Short Answer Questions
1) The X and Y chromosomes are considered the ________ chromosomes.
2) An allele that completely masks the expression of the other alleles is called ________.
3) Observable characteristics expressed by the genes for a trait are called the ________.
6) Removing a sample of the fluid surrounding the fetus for the purpose of studying the
chromosomes is a procedure called ________.
9) Define phenocopy.
11) How might carriers of deleterious genes be recognized?
Answer: Carriers of deleterious genes may be recognized if their offspring show symptoms of the
condition or disease caused by the deleterious gene. Because the genes are usually
recessive, they would show only phenotypically if the offspring received the recessive
genes from both parents. A pedigree analysis may be done to trace a particular trait
back through several generations. Blood chemistry tests (and DNA probing) may also
be done if particular genetic traits are suspected.
12) ________ disease is a disorder of brain lipid metabolism and is an example of a recessive trait.
13) When both parents are heterozygous for a recessive trait, they run a one-in-four chance that
the ________ trait will be expressed in their children.
20) When might amniocentesis be appropriate?
Answer: Amniocentesis might be performed any time a history of any genetic disability is
discovered in a family, especially if there are several occurrences in a family. This will
give the parents an early warning of any possible problem with the fetus. Other
ʺhigh-risk pregnanciesʺ (e.g. women over 35) may also suggest use of amniocentesis.
21) Describe briefly the three mechanisms that lead to genetic variability.
Answer: The three mechanisms that lead to genetic variability include independent assortment of
chromosomes, crossover of homologues, and random fertilization of eggs by sperm.
Each pair of homologous chromosomes synapses during meiosis I, forming a tetrad. The
alignment and orientation of the tetrads on the metaphase I spindle depend on chance.
The chromosomes are then randomly distributed to daughter cells. Because the way
each tetrad aligns is random, and many mother cells are undergoing meiosis
simultaneously, each alignment and each type of gamete occurs with the same
frequency as all others. Additional variation results from the crossing over and
exchange of chromosomal parts that occur during meiosis I. During meiosis, paternal
chromosomes can precisely exchange gene segments with the homologous maternal
ones, giving rise to recombinant chromosomes with mixed contributions from each
parent. A single human egg will be fertilized by a single sperm on a totally haphazard
Among members of the Fuzzy Wuzzy tribe, we will consider two pairs of genes:
F = fuzzy hair vs. f = straight hair,
T = long hair vs. t = short hair.
A homozygous, straight-shorthaired male marries a homozygous,fuzzy-longhaired female (P1 generation).
Their offspring (the F1 generation) intermarry and produce progeny (second generation) of four types: fuzzy-longhaired, fuzzy-shorthaired, straight-longhaired, and straight-shorthaired.
results follow a standard dihybrid pattern.
22) What is (are) the phenotype(s) of the first-generation offspring?
23) What is (are) the genotype(s) of the first-generation offspring?
24) A cross of two second-generation, straight-shorthaired individuals would yield what
25) What would the parental gametes be from a cross of two second-generation,
26) What would be the gametes of the first-generation individuals?
27) The second-generation types would have what phenotypes?
28) The second-generation phenotypes would follow what ratio? (Pair the number with a
phenotype in each case.)
29) What possible genotype(s) could the second-generation, fuzzy-longhaired individuals
30) What were the genotypes of the parental (P1) individuals?
31) Two tall red pea plants, when crossed, produced some offspring that were white and dwarf.
Assuming that tallness and redness are dominant, what are the genotypes of the parents?
1) In humans, farsightedness is inherited by possession of a dominant gene. If a man who is
homozygous for normal vision (aa) marries a woman who is heterozygous for farsightedness,
what proportion of their children would be expected to be farsighted?
2) Parents are informed after an amniocentesis that the results show a baby who has an extra
number 21 chromosome. Should there be concern and what might the problem be?
3) Jane and Allen have just discovered that their son is a hemophiliac. Neither of them has
hemophilia, and Allen claims that no such condition was ever expressed in his family. Jane
was told that her father was a hemophiliac and that problems resulting from this condition
caused his death. Allen has also been told that hemophilia can only be passed on to an
offspring by parents and not by grandparents; he believes that Jane was unfaithful and that
the child is not his. If you were a genetic counselor, what would you tell Allen?
Answer: The grandfather of the child was a hemophiliac and gave his X chromosome to Jane. She
did not express the disease because she has two X chromosomes, and the normal
dominant allele suppressed the expression of hemophilia (a male needs only one
hemophiliac allele to express the disease). Jane was not unfaithful, as she is a carrier
who would not be expected to express the recessive phenotype. The child probably
received the allele from Jane even though she did not have the disease
4) The folk singer, Woody Guthrie, died of Huntingtonʹs chorea. One of his parents also died of
this disease affecting the nervous system. The disease usually affects carriers between 25 and
45 years of age and is inherited as a Mendelian autosomal dominant trait. Using Punnett
squares, determine the probability that any of the three Guthrie offspring will have this
Answer: Woody had to have been a heterozygote Hh for the allele because the dominant
homozygous condition is lethal to the fetus. Woodyʹs wife did not have the disease so
she was not carrying it. Genetically they were Hh × hh. Using a Punnett square, the
probability of having a child with the disease would be 50%.
5) A 40-year-old pregnant woman is concerned about possible genetic defects in her unborn
fetus. Her physician recommends prenatal testing and advises her of two methods. Compare
and contrast amniocentesis with chorionic villi sampling relative to the time each can be
performed, and the relative advantages and disadvantages of each.
Answer: Amniocentesis is not normally done before the 14th week of pregnancy. The
disadvantage is the risk of injury to the fetus, but ultrasound visualization has
dramatically reduced the risk. Tests can be done on the fluid withdrawn to determine
the presence of chemicals that serve as markers for specific diseases. The cells
themselves are cultured and examined for DNA markers of genetic disease.
Karyotyping is also done to check for chromosomal abnormalities. Chorionic villi
sampling can be done at eight weeks. It is much faster but may be more risky for the
fetus. Karyotyping can be done on the rapidly dividing cells very quickly.
6) A family has four offspring belonging respectively to ABO blood groups A, B, O, and AB. Give
the genotypes and phenotypes of the parents.
7) Assume that the allele controlling brown eyes (B) is dominant over that controlling blue eyes
(b) in human beings. (In actuality, eye color in humans is an example of polygene inheritance,
which is much more complex than this.) A blue-eyed man marries a brown-eyed woman, and
they have six children, all brown-eyed. What is the most likely genotype of the father? What is
the most likely genotype of the mother? If the seventh child had blue eyes, what can you
conclude about the parentsʹ genotypes?
Answer: The most likely genotype of the father is bb (homozygous recessive) for the trait. The
most likely genotype for the mother is either Bb (heterozygous with both a dominant
and a recessive gene) or BB (homozygous dominant) for the trait. If the seventh child
had blue eyes, the motherʹs genotype would be Bb, and the fatherʹs genotype still would
8) Suppose an XcXc female marries an XcY man. (a) What is the probability of producing a
color-blind son? (b) What is the probability of producing a color-blind daughter? (c) What is
the probability of producing a daughter who is a carrier for the color-blind gene? (d) What is
the probability of having four sons in a row?
9) Assume that brown eyes (B) are dominant over blue (b); and right-handedness (R) is dominant
over left-handedness (r). A brown-eyed, right-handed man marries a blue-eyed,
right-handed woman. Their first child is brown-eyed and right-handed, and their second
child is blue-eyed and left-handed. What are the genotypes of the parents?
10) This is a first pregnancy for a 22-year-old woman. She is in her 16th week of pregnancy. She
is scheduled for an amniocentesis and expresses concern that the ʺbaby will be stuck with the
needle.ʺ What should the nurse say to the client?
11) A client is heterozygous for sickle-cell anemia. Explain why the client would have few or no
symptoms of sickle-cell anemia.
12) A nurse is providing genetic counseling to a couple who both have the sickle-cell anemia trait,
but not the disease. The couple is trying to decide whether or not to have a child. What is the
possibility a child would inherit the disease? What is one reason they might consider not
having a child?
Match the following:
1) Actual genetic makeup.
2) A chromosome pair that may
be very different in size.
3) Genes not expressed unless
they are present in
4) Situation in which an
individual has identical
alleles for a particular trait.
B) Sex chromosomes
5) Lack of skin pigmentation.
6) Rare type of dwarfism
resulting from an impaired
ability of the fetus to form
7) An unremitting, fatal nervous
system disease involving
degeneration of the basal
8) A condition of excessive
Diff: 2 Page Ref: 1151
9) A disorder of brain lipid
C) Huntingtonʹs disease
D) Tay-Sachs disease
E) Cystic fibrosis
10) Genes for the same trait that
have different expressions.
11) The gene allele that
suppresses or masks the
expression of the other allele.
12) Situation in which an
individual has different
alleles making up the
genotype for a particular trait.
13) Chromosomes regulating
most body characteristics.
1) When two genes are on the same chromosome, they are considered linked.
5) Chromosomes that are not directly involved with sex determination are called sex-linked.
9) Environmentally produced phenotypes that mimic conditions that may be caused by genetic
mutation are called phenocopies.
11) A Punnett square is a diagram that may be used to figure out the possible combinations of
genes for a trait.
12) The term lethal dominant gene indicates that the gene causes death only when the individual is
13) In incomplete dominance, the heterozygote has a phenotype intermediate between that of
homozygous-dominant and homozygous-recessive individuals.
14) The two equally useful avenues for detecting carriers are pedigrees and the use of Punnett
16) Genetic segregation implies that the members of the allele pair determining each trait are
distributed to different gametes during mitosis.
17) Genetic variation results from the crossing over and exchange of chromosomal parts that occur
during meiosis II.
19) It takes a major deviation in the epigenetic marks of a specific chromosome to result in a
devastating human illness.