Chapter 12 Flashcards
In a simple Mendelian monohybrid cross, true-breeding tall plants are crossed with short plants, and the F1 plants, which are all tall, are allowed to self-pollinate. What fraction of the F2 generation are both tall and heterozygous?
A. 1/8
B. 1/4
C. 1/3
D. 2/3
E. 1/2
E
The phenotype of an individual
A. depends at least in part on the genotype.
B. is either homozygous or heterozygous.
C. determines the genotype.
D. is the genetic constitution of the organism.
E. is either monohybrid or dihybrid.
A
Which statement about an individual that is homozygous for an allele is not true?
A. Each of its cells possesses two copies of that allele.
B. Each of its gametes contains one copy of that allele.
C. It is true-breeding with respect to that allele.
D. Its parents were necessarily homozygous for that allele.
E. It can pass that allele to its offspring.
D
Which statement about a test cross is not true?
A. It tests whether an unknown individual is homozygous or heterozygous.
B. The test individual is crossed with a homozygous recessive individual.
C. If the test individual is heterozygous, the progeny will have a 1:1 ratio.
D. If the test individual is homozygous, the progeny will have a 3:1 ratio.
E. Test cross results are consistent with Mendel’s model of inheritance for unlinked genes.
D
In the F2 generation of a dihybrid cross
A. four phenotypes appear in the ratio 9:3:3:1 if the loci are linked.
B. four phenotypes appear in the ratio 9:3:3:1 if the loci are unlinked.
C. two phenotypes appear in the ratio 3:1 if the loci are unlinked.
D. three phenotypes appear in the ratio 1:2:1 if the loci are unlinked.
E. two phenotypes appear in the ratio 1:1 whether or not the loci are linked.
B
The ABO blood groups in humans are determined by a multiple-allele system in which IA and IB are codominant and are both dominant to IO. A newborn infant is type A. The mother is type O. Possible phenotypes of the father are
A. A, B, or AB.
B. A, B, or O.
C. O only.
D. A or AB.
E. A or O.
D
In epistasis
A. nothing changes from generation to generation.
B. one gene alters the effect of another.
C. a portion of a chromosome is deleted.
D. a portion of a chromosome is inverted.
E. the behavior of two genes is entirely independent.
B
Linked genes
A. must be immediately adjacent to one another on a chromosome.
B. have alleles that assort independently of one another.
C. never show crossing over.
D. are on the same chromosome.
E. always have multiple alleles.
D
The genetic sex of a human is determined by
A. ploidy, with the male being haploid.
B. the Y chromosome.
C. X and Y chromosomes, the male being XX.
D. the number of X chromosomes, the male being XO.
E. Z and W chromosomes, the male being ZZ.
B
In humans, spotted teeth are caused by a dominant sex-linked gene. A man with spotted teeth whose father had normal teeth marries a woman with normal teeth. Therefore,
A. all of their daughters will have normal teeth.
B. all of their daughters will have spotted teeth.
C. all of their children will have spotted teeth.
D. half of their sons will have spotted teeth.
E. all of their sons will have spotted teeth.
B
Which of the following is not a characteristic of pea plants (shown) that caused Mendel to choose them for his studies of inheritance?
A. Flower morphology that made controlled cross-pollination possible
B. Prior studies on meiosis in this species
C. Existence of true-breeding strains
D. Presence of many well-defined, contrasting traits
E. Ease of cultivation
B
Which of the following statements about Mendel’s studies of monohybrid crosses (shown) is false?
A. Plants developing from seeds produced by crossing the two parent plants would be the F1 generation.
B. In studies of single characters, reciprocal crosses always gave the same results.
C. For each of the different monohybrid crosses, the trait that disappeared in the F1 generation reappeared in three-fourths of the F2 generation.
D. In monohybrid crosses, all F1 plants are heterozygous for the gene being studied.
E. In monohybrid crosses, approximately one-half of the F2 plants are homozygous for the gene being studied.
C
Which of the following statements about the interpretation of Mendel’s monohybrid studies is false?
A. Mendel’s monohybrid crosses allowed him to study a single gene in isolation.
B. A plant’s phenotype depends largely on which alleles are present for the gene being studied.
C. For each gene, the alleles from the two parents blend together to form a new phenotype.
D. Although F2 plants show only two phenotypes, three genotypes were present in this generation.
E. The alleles for a gene segregate independently of each other during gamete formation.
C
Which of the following statements about the dihybrid cross shown is false?
A. ssY- is a genotype that produces a recombinant phenotype.
B. The probability of obtaining the genotype ssYY in the F2 generation is 0.25 × 0.25 = 0.0625.
C. The physical basis for the law of independent assortment occurs during metaphase I of meiosis.
D. If the two genes shown in the cross were linked, you would expect mostly spherical green and wrinkled yellow F2 plants.
E. A test cross with F1 plants would produce one-fourth each of all four possible phenotypes.
D
The cross shown here depicts the F1 progeny resulting from mating true-breeding white and red snapdragons, which display incomplete dominance with respect to flower color. Complete the following sentence about the expected results in the F2 generation: According to the blending theory of inheritance, you should observe _______; whereas if the mode of inheritance is particulate with incomplete dominance, the expected results are _______.
A. 100% pink; 50% pink and 50% white
B. 100% pink; 75 percent red and 25% white
C. 100% pink; 25% white, 50% pink, and 25% red
D. 100% red; 50% pink and 50% white
E. 100% red; 25% white, 50% pink, and 25% red
C
The following figure shows clotting reactions for the ABO blood group system in humans. Select the following combination of terms that best describes the mode of inheritance illustrated by this system.
A. Codominance, pleiotropic
B. Codominance, multiple alleles
C. Codominance, multiple genes
D. Codominance, epistasis
E. Incomplete dominance, multiple alleles
B
Which of the following statements regarding quantitative variation of phenotypes is false?
A. Quantitative variation is also referred to as continuous variation.
B. Multiple genes with multiple alleles contribute to quantitative variation.
C. The environment contributes to quantitative variation.
D. Human height is an example of quantitative variation.
E. Identifying quantitative trait loci is relatively straightforward.
E
This figure shows gamete production in a wild-type female (left) and a black vestigial-winged male fruit fly (right) involved in a test cross. Which of the following genotypes are recombinant, and what would be the expected number of recombinants among 250 progeny if the map unit distance between these genes is 10 cM?
A. BbVgvg and bbvgvg; 10
B. BbVgvg and Bbvgvg; 25
C. bbvgvg and bbVgvg; 25
D. Bbvgvg and bbVgvg; 10
E. Bbvgvg and bbVgvg; 25
E
Gene Mapping: Given the genetic map for Drosophila melanogaster shown here, if you were to cross a YyMm female with a yymm male, what would be the expected number of YyMm individuals among 200 offspring?
A. 35
B. 70
C. 65
D. 100
E. 130
C
Which of the following statements about sex determination in humans (shown here) is false?
A. In both humans and Drosophila, the genetic constitution of sperm determines sex of the zygote.
B. XO individuals in both humans and Drosophila are female and sterile.
C. XXY individuals are female in Drosophila, but male in humans.
D. In humans, XX individuals with the SRY portion of the Y chromosome translocated onto another chromosome are male.
E. The Y chromosome plays no role in sex determination in Drosophila, whereas in humans it does.
B
Sex is determined in different ways in different species. Which of the following statements about sex determination in animals is false?
A. Reciprocal crosses involving genes on the X chromosome do not give identical results.
B. Sex determination mechanisms are only seen in dioecious species.
C. Male birds are hemizygous for genes on the sex chromosomes.
D. Male honeybees have only one set of autosomes.
E. In both Drosophila and humans, males are XY and females are XX.
C
In the following cross shown, the expected results are _______, whereas the reciprocal cross would produce _______.
A. all red-eyed flies; all white-eyed flies
B. all red-eyed flies; red-eyed females and white-eyed males
C. all red-eyed flies; red-eyed males and white-eyed females
D. red-eyed males and white-eyed females; red-eyed females and white-eyed males
E. red-eyed males and white-eyed females; all white-eyed flies
B
Which of the following statements about the two crosses shown here is false?
A. In cross 1, half of the daughters will be carriers and half will be color-blind.
B. In cross 1, all sons will be normal.
C. In cross 2, half of the daughters will be normal and half will be carriers.
D. In cross 2, half of the sons will be normal and half will be color-blind.
E. The Y chromosome plays no role in the determination of red-green color blindness.
A
Plants may show maternal inheritance of a trait because
A. the gene for the trait is present in plastid DNA.
B. the gene for the trait is present in mitochondrial DNA.
C. the gene for the trait is present on the Y chromosome.
D. plastids and mitochondria are often not present in sperm.
E. A, B, and D
E
Which of the following statements about bacterial conjugation is false?
A. There is transfer of DNA from the donor cell to the recipient cell and vice versa.
B. The donor and recipient cells recognize each other by sex pili.
C. DNA transfer occurs through a cytoplasmic bridge between the two cells.
D. DNA must be cut before it is transferred.
E. DNA from the donor may be integrated in the recipient’s chromosome.
A
Mendel concluded that each pea has two heritable units for each character, and each gamete receives one unit. Mendel’s “unit” is new referred to as a(n)
A. base pair of DNA.
B. character.
C. allele of a gene.
D. chromosome.
E. locus.
C
If a trait not expressed in the F1 generation reappears in the F2 generation, the inheritance of the trait in question is an example of
A. codominance.
B. dominance and recessiveness.
C. incomplete dominance.
D. epistasis.
E. a sex-linked trait.
B
If two strains of true-breeding plants that have different alleles for a certain character are crossed, the F1 progeny
A. are dihybrids.
B. are heterozygous for that character.
C. are also true-breeding.
D. have an intermediate phenotype.
E. have the same genotype as the dominant parent.
B
In the ABO blood type system,
A. A, B, and O are codominant.
B. A, B, and O are incompletely dominant.
C. A and B are codominant.
D. O is incompletely dominant to A and B.
E. A is dominant to B, and B is dominant to O.
C
The cross AaBb x AaBb is an example of a ___ cross and the result of such crosses led Mendel to propose what we now call ___.
A. dihybrid cross; law of independent assortment
B. dihybrid cross; law of segregation of genes
C. test cross; law of segregation of genes
D. test cross; law of independent assortment
E. selfcross; law of segregation of genes
A
The 9:3:3:1 ratio is obtained
A. through a dihybrid cross in which the genes are linked on the same chromosome.
B. through a dihybrid cross in which the genes are on different chromosomes.
C. when crossing over occurs.
D. in a test cross.
E. None of the above
B
The site on the chromosome occupied by a gene is called a(n)
A. allele.
B. region.
C. locus.
D. type.
E. phenotype.
C
In Mendel’s experiments, if the allele for tall (T) plants was incompletely dominant over the allele for short (t) plants, what offspring would have resulted from crossing two Tt plants?
A. 1/4 tall; 1/2 intermediate height; 1/4 short
B. 1/2 tall; 1/4 intermediate height; 1/4 short
C. 1/4 tall; 1/4 intermediate height; 1/2 short
D. All tall offspring
E. All intermediate height offspring
A
The physical appearance of a character is called
A. the genotype.
B. the phenotype.
C. an allele.
D. a chromosome.
E. a gene.
B
PTC tasting is a dominant trait. Finn and Maggie both can taste PTC but their daughter, Celia, cannot. If Finn and Maggie have a second child, what is the probability that this child also will not taste PTC?
A. 1/2
B. 0
C. 1
D. 3/4
E. 1/4
E
Segregation of alleles occurs
A. during gamete formation.
B. at fertilization.
C. during mitosis.
D. during the random combination of gametes to produce the F2 generation.
E. only in monohybrid crosses.
A
Which of the following statements about Mendelian genetics is false?
A. Alternative forms of genes are called alleles.
B. A locus is a gene’s location on its chromosome.
C. Only two alleles can exist for a given gene.
D. A genotype is a description of the alleles that represent an individual’s genes.
E. Individuals with the same phenotype can have different genotypes.
C
In a test cross, round peas of an unknown genotype were crossed with wrinkled peas of a known genotype (rr). If half of the offspring from that cross are round and half are wrinkled, what is the genotype of the unknown plant?
A. Heterozygous: Rr
B. Dominant: R
C. Homozygous recessive: rr
D. The genotype cannot be determined from the information given.
E. Homozygous dominant: RR
A
___ is the term for an allele that has more than one distinguishable phenotypic effect.
A. Epistasis
B. Multiple alleles
C. Codominance
D. Pleiotropy
E. Incomplete dominance
D
The genetic sex of a human is determined by
A. the number of X chromosomes, with XX and XXY being female.
B. the SRY gene located on the Y chromosome.
C. the number of copies of the HER gene, with two copies resulting in female development.
D. the number of Y chromosomes with YY being male and XY being female.
E. the ratio of autosomes to sex chromosomes.
B
It is predictable that half ot eh human babies born will be male and half will be female because
A. of the segregation of the X and Y chromosomes during male meiosis.
B. of the segregation of the X chromosomes during female meiosis.
C. all eggs contain an X chromosome
D. Both a and b
E. Both a and c
When reciprocal crosses rpoduce identical results, the trait is
A. sex-linked.
B. not sex-linked.
C. not autosomally inherited.
D. Both a and c
E. Both b and c
B
Suppose that a dihybrid cross produces a F2 generation with a phenotypic ratio close to 11:1:1:3 rather than 9:3:3:1. This ratio is indicative of:
A. independent assortment.
B. complete dominance.
C. non-disjunction.
D. gene linkage.
E. mutation of alleles.
D
Sex determination in birds and mammals is similar except that in birds, females are ___ while in mammals, females are ___.
A. heterogametic; homogametic
B. homogametic; heterogametic
C. haploid; heterogametic
D. diploid; heterogametic
E. None of the above
A
When a given trait is the result of multigene action, one of the genes may mask the expression of one or all other genes. this phenomenon is termed
A. epistasis.
B. epigenesis.
C. dominance.
D. incomplete dominance.
E. pleitropy.
A
White eyes is a recessive sex-linked (X-linked) trait in fruit flies. If a white-eyed female fruit fly is mated to a red-eyed male, their offspring should be
A. 50% red-eyed and 50% white-eyed for both sexes
B. all white-eyed for both sexes
C. all white-eyed males and all red-eyed females.
D. all white-eyed females and all red-eyed males.
E. 50% red-eyed males and 50% white-eyed males and all red-eyed females.
C
A human male carrying an allele for a trait on the X chromosome is
A. heterozygous.
B. homozygous.
C. hemizygous.
D. monozygous.
E. holozygous.
C
Red-green colorblindness is a recessive X-linked trait in humans. A woman with normal color vision marries a man who also has normal color vision. They have three children: a daughter with normal color vision, a son with normal color vision, and a son with colorblindness. Which of the following statements is true concerning this family?
A. The woman (mother) is a carrier of the colorblindness allele.
B. The woman (mother) had a mutation occur in the color vision gene in one of her eggs.
C. The man (gather) is a carrier of the colorblindness allele.
D. The man (father) must have a Y chromosome with the colorblindness allele.
E. The son with colorblindness much have two copies of the recessive colorblindness allele.
A
Which of the following observations support the idea that the gene controlling maleness is lcoated on the Y chromosome?
A. XO individuals are usually sterile, normal intelligence, female, with slight physical abnormalities.
B. XXY individuals are sterile males with long limbs.
C. XXX individuals are normal females.
D. Some men are XX but have a small piece of the Y attached to another chromosome.
E. All of the above are observations suggesting that the gene controlling maleness is on the Y chromosome.
E
A dramatic departure from expected phenotypic ratios may be the result of
A. environmental influences.
B. linkage.
C. epistasis.
D. gene interactions.
E. All of the above
E
segregation
separation of alleles during mitosis or homologous chromosomes during meiosis
epistasis
presence of an allele or gene determines whether another gene will be expressed
gene
unit of heredity
allele
alternate form(s) of a genetic character; found at same loci on homologous chromosomes
heterozygous
having different alleles of a given gene, e.g. Aa
expressivity
degree to which a genotype is expressed in the phenotype
can be affected by the environment
particulate theory
genes are hpysical entities that retain identities after fertilization
genotype
exact description of genetic constitution, wrt single trait or a larger set of traits
Punnett wquare
method of predicting results of a genetic cross based on parental genotypes
heritable trait
trait that is at least partially determined by genes
quantitative trait loci
set of genes that determines a complex character that exhibits quantitative variation
secondary sex determination
formation of secondary sex characteristics
dihybrid cross
cross between parents wrt alleles of two loci of interest
e.g. AABB, AaBb, aabb
true-breeding
genetic cross in which same result occurs every time wrt traits of interest
due to homozygous parents
