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CHAPTER 2
Why does spermatogenesis result in four spermatids, but oogenesis only results in one ovum? In oogenesis, the cell that becomes the ovum inherits most of the cytoplasm, whereas cytokinesis in spermatogenesis is equal.
An autotriploid has three sets of homologous chromosomes in each cell instead of the usual pairs of homologous chromosomes present in diploid individuals. Calculate the number of chromosomes in a diploid cell, give n = 16.
Suppose a sheep, which has 54 chromosomes, breeds with a goat, which has 60 chromosomes, and produces a geep. How many chromosomes would the geep have? Half of 54 + half of 60 = 57
What are the characteristics of a true-breeding plant line? Homozygous for the trait of interest AND when selfed, all offspring show the trait of interest, same phenotype as hybrid but differ in genotypes.
Which characteristics do eukaryotes have that prokaryotes do not normally have? Multiple chromosomes (prokaryotes have plasmids instead).
Telomeres are the natural ends of a chromosome.
What stage of mitosis do chromosomes arrive at spindle spores and the nuclear membrane reforms? Telophase
What stage of meiosis do homologous chromosomes line up in the middle? Metaphase I
Liam needs a microscope with high enough magnification to observe the bacteria cells he has cultured from Sauerkraut. Which of these microscopes has just enough magnification to allow viewing of bacteria? A scanning electron microscope (SEM) can achieve resolution greater than 1 nanometer.
A cell has 8 chromosomes in G1 of interphase. How many chromosomes will be found in anaphase of mitosis? 16 (# of chromosomes increases in anaphase as the two chromatids separate, each becoming their own chromosomes)
A cell has 8 chromosomes in G1 of interphase. How many chromosomes will be found in metaphase II? 4 ( but 8 chromatids, # of chromosomes is reduced by half after first meiotic division, meaning metaphase I has 8 chromosomes and 16 DNA molecule)
A standard petri dish has a surface area of 314 millimeters squared, which is equivalent to 314,000 micrometers squared. What is the maximum number of prokaryotic cells that could fit on the petri dish and completely cover the surface? 4000-400,000 cells
Assume that shugoshin is not degraded during meiosis. What would be the expected consequence of this abnormality? Sister chromatids would not separate at anaphase II.
Sister chromatids separate in which stage? Anaphase of mitosis and anaphase II of meiosis.
Jack is looking at a slide through a transmission electron microscope. He sees a cell lacking a nucleus and numerous smaller complex shaped viruses with icosahedral-shaped "heads" attacking the cell. What type of cell and viruses are present on the slide? The viruses are bacteriophages, and the cell is prokaryotic.
Eduardo is observing onion root tip cells under a light microscope. The cells have been dyed so that the chromosomes appear to be a darker purple on a lighter background. Most of the cells Eduardo observes will be in what phase? Interphase (the cell growth phase where the cell spends most of its time, ~70 percent of the cells should be expected to be in interphase).
CHAPTER 3/
The binomial expansion can be used to determine probability when there are several different orders in which a set of events can occur.
Which rule is used in conjunction with branch diagrams to predict the ratio of progeny with a particular set of characteristics? Multiplication.
The multiplication rule states that the probability of two or more independent events taking place together is calculated by multiplying their independent probabilities.
In cats, curled ears result from an allele ( Cu ) that is dominant to an allele ( cu ) for normal ears. Black color results from an independently assorting allele ( G ) that is dominant to an allele for gray ( g ). A gray cat homozygous for curled ears is mated with a homozygous black cat with normal ears. All the F1 cats are black and have curled ears. If two of the F1 cats mate, what phenotypic proportion is expected in the F2?
a) 1:1:1: b) 1:2: c) 9:3:3:1 (when we have a dihybrid cross of TWO heterozygotes) d) 3:
Gregor Mendel received broad scientific training during his early university studies. Which of these subjects do you think provided Mendel with the necessary knowledge to analyze phenotypic ratios from his experiments?
a) Mathematics b) Paleontology c) Entomology d) chemistry
Assume that an Aa animal produces four sperm from the same meiosis. A geneticist examines each of the four products of this meiosis and finds that one of them carries the a allele, one carries the A allele, one carries both the A and a alleles, and one has neither allele. This result is not consistent with which genetic concept?
a) principle of segregation (an example of non-disjunction, an error in meiosis that can occur when chromosomes are separating) b) conditional probability c) principle of independent assortment d) addition rule
When does the principle of independent assortment, Mendel's second law, occur in mitosis and/or meiosis?
a) anaphase I of meiosis b) anaphase of mitosis c) prophase I of meiosis d) prophase of mitosis
A gene is an inherited factor that helps determine a characteristic (it’s a specific sequence of DNA that codes for a protein and helps determine a characteristic).
Which genetic principle states that each individual possesses two alleles coding for a trait and that these alleles separate when gametes are formed?
a) chromosome theory of inheritance b) principle of segregation (then they randomly unite at fertilization) c) concept of dominance d) principle of independent assortment
What would be the phenotypic ratio produced by a cross between AaBb and aabb?
Suppose two independently assorting genes are involved in the pathway that determines fruit color in squash. These genes interact with each other to produce the squash colors seen in the grocery store. At the first locus, the W allele codes for a dominant white phenotype, whereas the w allele codes for a colored squash. At the second locus, the allele Y codes for a dominant yellow phenotype, and the allele y codes for a recessive green phenotype. The phenotypes from the first locus will always mask the phenotype produced by the second locus if the dominant allele (W) is present at the first locus. This masking pattern is known as dominant epistasis. A dihybrid squash, WwYy, is selfed, and produces 128 offspring. How many offspring are expected to have each of the following phenotypes?
A ratio of 12:3:1 is produced because of the masking effect that a dominant allele for the first gene has on the second gene.
A yellow female Labrador retriever was mated with a brown male. Half of the guppies were brown, and half were yellow. Explain how the same female, when mated with a different brown male, could produce only brown offspring? The first male was Bb Ee, and the second male was bb EE.
Why are the offspring generated from interspecies crosses often sterile? Gametes are not formed correctly because the chromosomes are unable to segregate properly during meiosis in the hybrid offspring.
In fruit flies, gray bodies ( G ) are dominant over black bodies ( g ), and red eyes ( R ) are dominant over orange eyes ( r ). If a fly that is homozygous dominant for both traits ( GGRR ) is crossed with a fly that is homozygous recessive for both traits ( ggrr ), what is the predicted genotype of the offspring? GgRr.
Suppose Maria wants to breed guinea pigs that are black with short fur. However, when she bred several guinea pigs that were black with short fur, she found that there were four different offspring phenotypes. Based on the offspring data provided, determine the number of genes and alleles that control these phenotypes.
1 gene with 4 alleles each would present equal proportions, 4 genes with 1 allele each will only present one phenotype. So, our answer is 2 alleles with 2 alleles each****.
In peas, inheritance of seed shape, plant size, and seed color follow a pattern of Mendelian inheritance. For seed shape, round peas, 𝑅 , are dominant to wrinkled peas, 𝑟 ; for plant size, tall plants, 𝑇 , are dominant to short plants, 𝑡 ;
for seed color, yellow seeds, 𝑌, are dominant to green seeds, 𝑦. Suppose a heterozygous plant, 𝑅𝑟𝑇𝑡𝑌𝑦, is selfed and the phenotype of the resulting offspring is determined. Calculate the chi-square value for this experiment.
For trihybrid cross, our phenotypic ratio is 27:9:9:9:3:3:3:1 out of 64.
Suppose a man is heterozygous for heterochromia, an autosomal dominant disorder which causes 2 different-colored eyes in an individual, producing 25 offspring with his normal-eyed wife. Of their children, 16 were heterochromatic and 9 were normal. Calculate the chi-square value for this observation and identify the statement that best interprets the results of the chi-square analysis.
An autosomal ‑ dominant condition is caused by a dominant allele. The probability of inheritance from their affected biological parents is 50%.
Imagine that a scientist studies two traits in cattle. The scientist noticed that oval is dominant over triangular with regard to snout shape. Additionally, long is dominant over short with regard to tail length. To determine if these traits are linked, two individuals that are heterozygous for both traits were crossed. The data in the table represent the number of offspring produced by this hybrid cross. Phenotypic ratio represents the predicted proportion of offspring with each set of traits that would be produced if the traits independently assort.
CHAPTER 5
Epigenetics involves reversible changes to DNA that affect how genes are expressed.
Characteristics that exhibit many overlapping phenotypes are called continuous characteristics.
What is the definition of compound heterozygote? An individual who carries two different alleles at a locus that result in a recessive phenotype.
If the color of the pepper Capsicum annuum were only influenced by a single locus, what would be the phenotype ratio of the F2 generation from a homozygous red and homozygous cream P cross?
A father can pass an X-linked trait to his daughter; can he also pass a sex-influenced characteristic to her? Yes, sex-influenced characteristics are determined by genes on autosomes (X-linked traits are located on the X chromosome, sex-influenced characteristics are determined by genes on autosomes that are expressed differently in males and females due to hormonal influences).
In chickens, comb shape is determined by alleles at two loci (R, r and P, p). A walnut comb is produced when at least one dominant allele R is present at one locus and at least one dominant allele P is present at a second locus (genotype R_ P_). A rose comb is produced when at least one dominant allele is present at the first locus and two recessive alleles are present at the second locus (genotype R_ pp). A pea comb is produced when two recessive alleles are present at the first locus and at least one dominant allele is present at the second (genotype rr P_). If two recessive alleles are present at the first and at the second locus (rr pp), a single comb is produced. A walnut is crossed with a pea chicken and the offspring consists of 3/8 walnut, 3/8 pea, 1/8 rose, and 1/8 single. What are the probable genotypes of the parents? Rr Pp x rr Pp
What is the definition of a temperature-sensitive allele? An allele whose product is functional only at certain temperatures (a conditional mutation where an organism displays a normal, wild-type, phenotype at a permissive temperature but a mutant (often non-functional or lethal) phenotype at a different, restrictive temperature).
Assume that you discover a new species of snail. Its shells can either be red (RR), pink (Rr), or white (rr) in color. You cross a red male who is of Rr genotype with a white female who is of Rr genotype. All the offspring are pink in phenotype, but 1/2 are Rr in genotype, 1/4 are RR in genotype, and 1/4 are rr in genotype. How can this outcome be
best explained? A genetic maternal effect is involved (while the offspring have a 1:2:1 genotypic ratio (1/4 RR, 1/ Rr, 1/4 rr), they all display the pink phenotype of the mother – Rr).
An allele is only expressed at temperatures greater than 30°C. This is an example of a temperature- sensitive allele.
The autosomal gene bicoid (bcd) has been studied in Drosophila and found to show a genetic maternal effect. The mutant allele (bcd-) is recessive and leads to death during embryogenesis. A particular Drosophila embryo dies during embryogenesis because of this gene. What is the genotype of the embryo's mother and the genotype of her maternal grandmother? the embryo's mother is bcd-bcd- and her grandmother is bcd+bcd- (grandmother must be heterozygous in order to have a viable bcd-bcd- daughter)
A cross between two yellow heterozygous mice (Yy) that both contain a lethal allele will produce which genotypic ratio among the progeny? 2 Yy: 1 yy (homozygous YY mice die early in development and do not appear among the progeny, resulting in a 2:1 ratio of Yy (yellow) to yy (non-yellow) in the offspring)
Huntington's disease (HD) is an autosomal dominant condition that is often not obviously expressed until middle age. However, children receiving the mutant allele from their father often express the condition earlier in life than he did. What term describes this situation? Anticipation.
Assume that a continuous characteristic is caused by six gene pairs, each locus with two alleles. How many different genotypes are possible for this characteristic? 729 (3^6 = 729)
Assume that a continuous characteristic is caused by six gene pairs, each locus with two alleles. How many different genotypes are possible for this characteristic? IAIi (it’s the only genotype that has both alleles for type A and O)
Calculate the number of possible genotypes when 3 loci, each with 2 alleles, interact to affect a characteristic.
Shell coiling of the snail Lymnaea peregra results from a genetic maternal effect. An autosomal allele for a right-handed, or dextral, shell (s+) is dominant over the allele for a left-handed, or sinistral, shell (s). A dextral male snail mates with a dextral female snail. This cross produces only offspring with sinistral shells. What is the genotype of the female parent? ss (dextral shell, s+, is dominant over the allele for sinistral shells, s. A female parent with genotype ss will produce only sinistral offspring)
In a certain species of animal, two independently assorting genes, A and B, interact in a complementary manner to produce horns for both sexes. Animals that are homozygous recessive for one or both genes (aaB_, A_bb or aabb)
Penile hypospadias, a birth defect in male humans in which the urethra opens on the shaft instead of at the tip of the penis, results from an autosomal dominant gene in some families. Females who carry the gene show no effects. What type of trait is this birth defect an example of? A sex-limited trait because the condition occurs only in males and the gene involved is autosomal (inherited by both sexes but are silenced in one sex).
The first cloned cat, CarbonCopy (CC), was tabby, while the cat she was cloned from, Rainbow, was calico. The surrogate mother was a tabby. Select the explanation that best explains why CC would never have been identical in pattern to Rainbow. The pattern of X-chromosome inactivation is established randomly in a cell lineage.
A black female cat is mated with an orange male cat. They produce two tortoiseshell females, two black males, one orange female, and one tortoiseshell male. Orange and black fur color are encoded by different alleles of the same X-linked fur color gene. What sex chromosome do the orange female and the tortie male offspring have? Select the most likely explanations for the sex chromosome types. The orange female has only one X chromosome (it came from her father), and the tortie male is XXY (random X inactivation in XXY causes orange and black patches).
Color blindness is a sex-linked recessive trait. A female is color blind in one eye but not both. Select the explanation for this condition. Is it possible for a male to have different color-blindness phenotypes in each eye? Random X-chromosome inactivation. Yes, in an XXY male where each eye has alternate X inactivation.
CHAPTER 6
Alpers' disease is a mitochondrially inherited condition that can cause a variety of symptoms, including seizures, dementia, blindness, liver dysfunction, and cerebral degeneration. Which of the individuals are affected by this disease?
A mitochondrial disease = inherited if biological mother is affected = all sexes of children affected
The pedigree describes a family with a rare genetic condition. Individual 11 is known to have no affected alleles. Use the pedigree to determine the mode of inheritance of the condition. SEX-LINKED RECESSIVE.
Skips generation = recessive = individual 16 can only express condition through hemizygosity (on X-chromosome)
Individual 11 has 2 unaffected alleles = his son can only have 1 affected allele
An X-linked recessive gene causes red-green colour blindness in humans. Suppose John and Cathy have normal vision. Cathy gives birth to color-blind son and color-blind daughter. John files for a divorce claiming that he is not the father of at least one of the children. Which statement describes John’s paternity claim? He cannot be the father of Cathy’s daughter (because for a daughter to be affected for an x-linked recessive condition, father must be affected).
Suppose that various members of a family spanning 4 generations have a mutant phenotype that is very rare. What is the most likely mode of inheritance for this rare phenotype? Autosomal dominant and sex-limited to males, because the mutant allele can be inherited from an unaffected mother.
Sex-limited because the trait is only expressed physically in one sex (males).
NOT Y-linked because affected fathers did not pass trait to ALL his sons
Ectrodactyly is a rate condition in which the fingers are absent and the hand is split. This inheritance is most likely? Autosomal recessive because the trait skips generations.
Dizygotic twinning appears to be heritable and varies in frequency among ethnic groups. Monozygotic twinning is not heritable and occurs equally among ethnic groups. What statement explains the genetic basis for this? The biological mother’s genotype affects the rate of dizygotic twinning, whereas monozygotic tanning results from a chance event during development.
offspring only express the trait when the parents express the trait or are carriers.
Testing for genetic disorders in newborn infants is called newborn screening.
A phenotypically normal woman has a son with the sex-linked condition of red–green color blindness. Assigning c for the recessive allele for the condition and c+ for the normal allele, what is the likely genotype of this woman? Xc+Xc
A four-year old boy and his two-year old brother share what proportion of their genes (alleles) compared to a set of male monozygotic twins? The brothers share one half of their genes, while the twins have all identical genes.
Preimplantation genetic diagnosis determines the presence of disease-causing genes in a(n) embryo at an early stage, while prenatal genetic testing determines this presence in a(n) developing fetus.
How are adoption studies used to separate the effects of genes and the environment in the study of human characteristics? Adoption studies assume that the environments of biological and adoptive families are independent.
Which was the most important consideration in choosing genetic conditions for mandatory newborn screening? Availability of effective treatments and early interventions.
Which common genetic ratio would be easiest to recognize among the offspring in a human family? 1:1 (results from the mating of a heterozygous parent and a homozygous recessive parent)
Interpreting many genetic tests, even with professional medical care provided, is often difficult because of all of these reasons EXCEPT the number and complexity of genetic tests and rates of concordance (presence of multiple allele mutations causing same condition, influence of environmental factors, and incomplete penetrance might make interpreting genetic tests hard).
How might genetic testing lead to genetic discrimination? Employment and health insurance.
How is the influence of genetic factors indicated for a particular trait? A higher concordance in monozygotic twins than in dizygotic twins.
While monozygotic twins are often assumed to be 100% genetically identical, they may not express their genes in an identical fashion. Which of these would be the most likely reason why female monozygotic twins would not have identical patterns of gene expression? Random nature of X inactivation means the two twins will have different X-linked alleles expressed in different cell types.
Twin studies show that asthma is caused by a combination of what factors? Environment and heritability.
CHAPTER 7
The absence of one or more of the bands that are normally seen on a chromosome reveals the presence of a chromosomal deletion.
Rates of recombination vary among species, among and along chromosomes, and even between males and females.
Genes located close together on the same chromosome belong to the same linkage group.
Recombination hotspots in humans are often found near, but not within, active genes.
Consider the cross Aa Bb × aa bb. Assume loci A and B are completely linked with no crossing over. What proportion of the progeny will have genotype Aa Bb? One-half (only two types, AaBb and aabb, are produced in equal proportions)
To set up a three-point testcross for loci A, B, and C, you need progeny that are heterozygous for all three loci (i.e. Aa Bb Cc). Which parental cross would you use to obtain the heterozygotes? AA BB CC x aa bb cc
In human–mouse somatic-cell hybrids, the human chromosomes tend to be lost, whereas the mouse chromosomes are retained.
A double crossover event between the same two nonsister chromatids occurs during prophase I of meiosis. What happens to the unaffected nonsister chromatids? They enter nonrecombinant gametes.
A testcross is made by crossing a heterozygous Aa Bb Cc mouse with a aa bb cc mouse. The total testcross progeny consists of 100 Aa Bb Cc, 100 Aa Bb cc, 100 aa bb Cc, and 100 aa bb cc. Which of these statements is CORRECT? A and B are tightly linked, but C is assorting independently (there’s no Aa bb or aa Bb progeny)
Assume that in 100 meiotic events, 12 single crossover events occur between two genes a and b. How many of the resulting 400 chromatids from these 100 meiotic events should be recombinant for a and b? 24 (when a crossover event takes place, only half of the resulting gametes will be recombinant; 0.12 × 200 = 24).
Which of the answers is NOT a difference between a heterokaryon and a typical cell from an organism? A heterokaryon cannot successfully complete mitosis or meiosis.
What is the probability of double-recombinant progeny if the single recombination frequencies of progeny are 15% and 20%? 3% (0.15 x 0.20 = 0.03 = 3%)
A female mouse of genotype CD/cd is testcrossed to a male of cd/cd genotype. In 88% of the meioses, there is no crossover event between the two genes. In 12% of the meioses, there is one crossover between the two genes. What proportion of the offspring will be Cd/cd? 3% (Rf = 0.88/0.12 = 6.67, desired genotype is half of that)
What is the probe for the gene for the fluorescence in situ hybridization (FISH) method? A single-stranded DNA complementary to the gene of interest.
The interference among three genes is 0.2. What is the coefficient of coincidence? COC = 1 - 0.2 = 0.
Two genes have been both assigned to chromosome 12 by somatic-cell hybridization analysis. However, when lod-score analysis is performed, the genes appear to be assorting independently. The most likely reason for the
- Assuming that gene order is as determined in the original animation, what would be the least common three‑point test cross progeny types if, in the triple heterozygous female parent, the scarlet eye and spineless bristle mutations were coupled and the ebony body mutation was in repulsion? ebony, spineless progeny and scarlet progeny
- Could gene order be determined if rather than eight phenotypes of progeny, as seen in the animation, there were only six phenotypes of progeny observed, representing three reciprocal progeny groups? Yes, it can be, assuming that the double recombinants are the two types of predicted progeny that are missing and that there are zero of each type.
- In the animation, the original triple‑heterozygous female fly had all of the mutations in a coupled arrangement. If, instead, the original wild‑type, triple‑heterozygous female were the result of two true breeding parents, one being scarlet and ebony and the other being spineless, which of the statements would be true? Wild ‑ type and triple ‑ mutant phenotypes would be the least frequent progeny in the three ‑ point test cross.
Perform a chi-square test of independence, using a 2x2 contingency table, on the data provided in figure to determine if the genes for flower colors and pollen shape in sweat peas are assorting independently. Give the chi-square value, degrees of freedom, and associated probability.
Daniel McDonald and Nancy Peer determined that eyespot (a clear spot in the center of the eye) in flour beetles is caused by an X-linked gene (es) that is recessive to the allele for the absence of eyespot (es+). They conducted a series of crosses to determine the distance between the gene for eyespot and a dominant X-linked gene for striped
- Does the X2 value support the hypothesis that the quiver and vestigial genes assort independently? Why or why not? Use the partial table of critical values for X2 calculations to test this hypothesis. No, the 𝑋 2 = value indicates that the observed progeny are significantly different from what would be expected with independent assortment of the two genes.
In a testcross involving two heterozygous genes, equal numbers of recombinant and nonrecombinant progeny are produced. From this result, what can be concluded? The genes are not linked.
Three-point testcrosses are often used to map genes. The two least frequent classes from such crosses usually represent which types of progeny? Double-crossover progeny.
A geneticist is using a three‑point testcross to map three linked Drosophila recessive mutations called a, b, and c, where a is associated with anomalous gait, b is associated with buckled wings, and c is associated with curved bristles. She first crosses homozygous anomalous, buckled flies to homozygous curved flies. Next, she testcrosses the F1 progeny to anomalous, buckled, curved flies. She obtains 1000 progeny distributed as shown. From this data, calculate the map distance between b and c.
