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Questions and Answers of Biology

Explain why the products of meiosis may not be genetically identical, whereas the products of mitosis are.
What is a homolog? With regard to genes and alleles, how are homologs similar to and different from each other?
The period between meiosis I and meiosis II is called interphase II. Does DNA replication take place during interphase II?
List several ways in which telophase appears to be the reverse of prophase and prometaphase.
Corn has 10 chromosomes per set, and the sporophyte of the species is diploid. If you performed a karyotype, what is the total number of chromosomes you would expect to see in the following types of
The arctic fox has 50 chromosomes (25 per set), and the common red fox has 38 chromosomes (19 per set). These species can interbreed to produce viable but infertile offspring. How many chromosomes
Let's suppose that a gene affecting pigmentation is found on the X chromosome (in mammals or insects) or the Z chromosome (in birds) but not on the Y or W chromosome. It is found on an autosome in
Describe the cellular differences between male and female gametes.
At puberty, the testes contain a finite number of cells and produce an enormous number of sperm cells during the life span of a male. Explain why testes do not run out of spermatogonia! cells.
Describe the timing of meiosis I and II during human oogenesis.
Three genes (A, B, and C) are found on three different chromosomes. For the following diploid genotypes, describe all of the possible gamete combinations. A. Aa Bb Cc B. AA Bb CC C. Aa BB Cc D. Aa bb
A phenotypically normal woman with an abnormally long chromo-some 13 (and a normal homolog of chromosome 13) marries a phe-notypically normal man with an abnormally short chromosome 11 (and a normal
What is a sister chromatid? Are sister chromatids genetically similar or identical? Explain.
Assuming that such a fly would be viable, what would be the sex of a fruit fly with the following chromosomal composition? A. One X chromosome and two sets of autosomes B. Two X chromosomes, one Y
What would be the sex of a human with the following numbers of sex chromosomes? A. XXX B. X (also described as X0) C. XYY D. XXY
How does the attachment of kinetochore microtubules to the kinetochore differ in metaphase of meiosis I from metaphase of mitosis? Discuss what you think would happen if a sister chromatid was not
For the following events, specify whether they occur during mitosis, meiosis I, or meiosis II: A. Separation of conjoined chromatids within a pair of sister chromatids B. Pairing of homologous
Describe the key events during meiosis that result in a 50% reduction in the amount of genetic material per cell.
A cell is diploid and contains three chromosomes per set. Draw the arrangement of chromosomes during metaphase of mitosis and metaphase of meiosis I and II. In your drawing, make one set dark and the
When studying living cells in a laboratory, researchers sometimes use drugs as a way to cause cells to remain in a particular phase of the cell cycle. For example, aphidicolin inhibits DNA synthesis
Discuss why crosses (i.e., the experiments of Mendel) and the microscopic observations of chromosomes during mitosis and meiosis were both needed to deduce the chromosome theory of inheritance.
Female flies with white eyes and miniature wings (both X-linked recessive traits) were crossed to male flies with red eyes and normal wings. On rare occasions, female offspring were produced with
Experimentally, how do you think researchers were able to determine that the Y chromosome causes maleness in mammals, whereas the ratio of X chromosomes to the sets of autosomes causes sex
In Morgan's experiments, which result do you think is the most convincing piece of evidence pointing to X-linkage of the eye color gene? Explain your answer.
In his original studies of Figure 3.18, Morgan first suggested that the original white-eyed male had two copies of the white-eye allele. In this problem, let's assume that he meant the fly was XWYW
How would you set up crosses to determine if a gene was Y linked versus X linked?
Occasionally during meiosis, a mistake can happen whereby a gamete may receive zero or two sex chromosomes rather than one. Calvin Bridges made a cross between white-eyed female flies and red-eyed
Let's suppose that you have karyotyped a female fruit fly with red eyes and found that it has three X chromosomes instead of the normal two. Although you do not know its parents, you do know that
White-eyed flies have a lower survival rate than red-eyed flies. Based on the data in Figure 3.18, what percentage of white-eyed flies survived compared with red-eyed flies, assuming 100% survival of
In Figure 3.18, Morgan obtained a white-eyed male fly in a population containing many red-eyed flies that he thought were true-breeding. As mentioned in the experiment, he crossed this fly with
A diploid eukaryotic cell has 10 chromosomes (5 per set). As a group, take turns having one student draw the cell as it would look during a phase of mitosis, meiosis I, or meiosis II; then have the
Discuss the principles of the chromosome theory of inheritance. Which principles were deduced via light microscopy, and which were deduced from crosses? What modern techniques could be used to
Describe the differences among dominance, incomplete domi¬nance, codominance, and overdominance.
A woman with type B blood has a child with type O blood. What are the possible genotypes and blood types of the father?
A type A woman is the daughter of a type O father and type A mother. If she has children with a type AB man, what are the following probabilities? A. A type AB child B. A type O child C. The first
In Shorthorn cattle, coat color is controlled by a single gene that can exist as a red allele (R) or white allele (r). The heterozygotes (Rr) have a color called roan that looks less red than the RR
In chickens, the Leghorn variety has white feathers due to an autosomal dominant allele. Silkies have white feathers due to a recessive allele in a second (different) gene. If a true-breeding white
Hemophilia is an X-linked recessive trait in humans. If a heterozygous woman has children with an unaffected man, what is the probability of the following combinations of children? A. An affected
With regard to scurs in cattle (a sex-influenced trait), a cow with no scurs whose mother had scurs had offspring with a bull with scurs whose father had no scurs. What are their probabilities of
Discuss the differences among sex-influenced, sex-limited, and sex-linked inheritance. Give examples.
In cats, a temperature-sensitive allele produces the Siamese phenotype in which the cooler extremities are dark and the warmer trunk area is lighter. A Siamese cat that spends most of its time
A true-breeding male fly with light-eosin eyes is crossed to a white-eyed female that is heterozygous for the wild-type (C) and cream alleles (ca). What are the expected proportions of their
The trait of hen- versus cock-feathering is a sex-limited trait controlled by a single gene. Females always exhibit hen-feathering as do HH and Hh males. Only hh males show cock-feathering. Starting
In the pedigree shown here for a trait determined by a single gene (affected individuals are shown in black), state whether it would be possible for the trait to be inherited in each of the following
The pedigree shown here also concerns a trait determined by a single gene (affected individuals are shown in black). Which of the following patterns of inheritance are possible?A. RecessiveB.
Let's suppose you have pedigree data from thousands of different families involving a particular genetic disease. How would you decide whether the disease is inherited as a recessive trait as opposed
Compare phenotypes at the molecular, cellular, and organism levels for individuals who are homozygous for the hemoglobin allele, HbAHhA, and the sickle cell allele, HbSHbS.
A very rare dominant allele that causes the little finger to be crooked has a penetrance value of 80%. In other words, 80% of heterozygotes carrying the allele will have a crooked little finger. If a
A sex-influenced trait in humans is one that affects the length of the index finger. A "short" allele is dominant in males and recessive in females. Heterozygous males have an index finger that is
Three coat-color patterns that occur in some breeds of horses are termed cremello (beige), chestnut (brown), and palomino (golden with light mane and tail). If two palomino horses are mated, they
What is meant by a gene interaction? How can a gene interaction be explained at the molecular level?
Let's suppose a recessive allele encodes a completely defective protein. If the functional allele is dominant, what does that tell you about the amount of the functional protein that is sufficient to
A nectarine is a peach without the fuzz. The difference is controlled by a single gene that is found in two alleles, D and d. At the molecular level, would it make more sense to you that the
The blood serum from one individual (let's call this person individual 1) is known to agglutinate the red blood cells from a second individual (individual 2). List the pairwise combinations of
Which blood phenotypes (A, B, AB, and/or O) provide an unambiguous genotype? Is it possible for a couple to produce a family of children with all four blood types? If so, what would the genotypes of
Mexican hairless dogs have little hair and few teeth. When a Mexican hairless is mated to another breed of dog, about half of the puppies arc hairless. When two Mexican hairless dogs are mated to
Certain species of summer squash exist in long, spherical, or disk shapes. When a true-breeding long-shaped strain was crossed to a true-breeding disk-shaped strain, all of the F1 offspring were
In a species of plant, two genes control flower color. The red allele (R) is dominant to the white allele (r); the color-producing allele (C) is dominant to the non-color-producing allele (c). You
In Drosophila, red eyes is the wild-type phenotype. Several different genes (with each gene existing in two or more alleles) are known to affect eye color. One allele causes purple eyes, and a
As mentioned in Experimental Question E12, red eyes is the wild-type phenotype in Drosophila, and several different genes (with each gene existing in two or more alleles) affect eye color. One allele
Let's suppose you were looking through a vial of fruit flies in your laboratory and noticed a male fly that has pink eyes. What crosses would you make to determine if the pink allele is an X-linked
When examining a human pedigree, what features do you look for to distinguish between X-linked recessive inheritance and autosomal recessive inheritance? How would you distinguish X-linked dominant
The cream allele is a modifier of eosin and the cream allele is autosomal. By comparison, the red and eosin alleles are X-linked. Based on these ideas, conduct a chi square analysis to determine if
In chickens, some varieties have feathered shanks (legs), but others do not. In a cross between a Black Langhans (feathered shanks) and Buff Rocks (unfeathered shanks), the shanks of the F1
In sheep, the formation of horns is a sex-influenced trait; the allele that results in horns is dominant in males and recessive in females. Females must be homozygous for the horned allele to have
A particular breed of dog can have long hair or short hair. When true-breeding long-haired animals were crossed to true-breeding short-haired animals, the offspring all had long hair. The F2
In the clover butterfly, males are always yellow, but females can be yellow or white. In females, white is a dominant allele. Two yellow butterflies were crossed to yield an F1 generation consisting
The Mic2 gene in humans is present on both the X and Y chromosome. Let's suppose the Mk2 gene exists in a dominant Mic2 allele, which results in normal surface antigen, and a recessive mic2 allele,
Duroc Jersey pigs are typically red, but a sandy variation is also seen. When two different varieties of true-breeding sandy pigs were crossed to each other, they produced F, offspring that were red.
As discussed in this chapter, comb morphology in chickens is governed by a gene interaction. Two walnut comb chickens were crossed to each other. They produced only walnut comb and rose comb
In certain species of summer squash, fruit color is determined by two interacting genes. A dominant allele, W, determines white color, and a recessive allele (w) allows the fruit to be colored. In a
Let's suppose a gene exists as a functional wild-type allele and a nonfunctional mutant allele. At the organism level (i.e., at the level of visible traits), the wild-type allele is dominant. In a
A true-breeding rooster with a rose comb, feathered shanks, and cock-feathering was crossed to a hen that is true-breeding for pea comb and unfeathered shanks but is heterozygous for hen-feathering.
In oats, the color of the chaff is determined by a two-gene interaction. When a true-breeding black plant was crossed to a true-breeding white plant, the F1 generation was composed of all black
Define the term epigenetic inheritance, and describe two examples.
With regard to the numbers of sex chromosomes, explain why dosage compensation is necessary.
What is a Barr body? How is its structure different from that of other chromosomes in the cell? How does the structure of a Barr body affect the level of X-linked gene expression?
Among different species, describe three distinct strategies for accomplishing dosage compensation.
Describe when X-chromosome inactivation occurs and how this leads to phenotypic results at the organism level. In your answer, you should explain why XCI causes results such as variegated coat
How many Barr bodies would you expect to find in humans with the following abnormal compositions of sex chromosomes? A. XXY B. XYY C. XXX D. XO (a person with just a single X chromosome)
What is the spreading phase of X-chromosome inactivation? Why do you think it is called a spreading phase? Discuss the role of the Xist gene in the spreading phase of XCI.
Describe the inheritance pattern of maternal effect genes. Explain how the maternal effect occurs at the cellular level. What are the expected functional roles of the proteins that are encoded by
When does the erasure and reestablishment phase of genomic imprinting occur? Explain why it is necessary to erase an imprint and then reestablish it in order to always maintain imprinting from the
In what types of cells would you expect de novo methylation to occur? In what cell types would it not occur?
On rare occasions, people are born with a condition known as uniparental disomy. It happens when an individual inherits both copies of a chromosome from one parent and no copies from the other
Genes that cause Prader-Willi syndrome and Angelman syndrome are closely linked along chromosome 15. Although people with these syndromes do not usually reproduce, let's suppose that a couple
How is the process of X-chromosome inactivation similar to genomic imprinting? How is it different?
What is extranuclear inheritance? Describe three examples.
What is a reciprocal cross? Suppose that a gene is found as a wild-type allele and a recessive mutant allele. What would be the expected outcomes of reciprocal crosses if a true-breeding normal
Among different species, does extranuclear inheritance always follow a maternal inheritance pattern? Why or why not?
Extranuclear inheritance often correlates with maternal inheritance. Even so, paternal leakage is not uncommon. What is paternal leakage? If a cross produced 200 offspring and the rate of
Discuss the structure and organization of the mitochondrial and chloroplast genomes. How large are they, how many genes do they contain, and how many copies of the genome are found in each organelle?
A maternal effect gene exists in a dominant N (normal) allele and a recessive n (abnormal) allele. What would be the ratios of genotypes and phenotypes for the offspring of the following crosses? A.
Explain the likely evolutionary origin of mitochondrial and chloroplast genomes. How have the sizes of the mitochondrial and chloroplast genomes changed since their origin? How has this occurred?
Which of the following traits or diseases are determined by nuclear genes? A. Snail coiling pattern B. Prader-Willi syndrome C. Leber hereditary optic neuropathy
Acute murine leukemia virus (AMLV) causes leukemia in mice. This virus is easily passed from mother to offspring through the mother's milk. (Even though newborn offspring acquire the virus, they may
Describe how a biparental pattern of extranuclear inheritance would resemble a Mendelian pattern of inheritance for a particular gene. How would they differ?
A Drosophila embryo dies during early embryogenesis due to a recessive maternal effect allele called bicoid. The wild-type allele is designated bicoid*. What are the genotypes and phenotypes of the
For Mendelian traits, the nuclear genotype (i.e., the alleles found on chromosomes in the cell nucleus) directly influences an offspring's traits. In contrast, for non-Mendelian inheritance patterns,
Suppose a maternal effect gene exists as a normal dominant allele and an abnormal recessive allele. A mother who is phenotypically abnormal produces all normal offspring. Explain the genotype of the

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