Ch. 4 - Extensions of Mendelian Genetics
Back
- In this chapter, we focused on extensions and modifications of Mendelian principles and ratios. In the process, we encountered many opportunities to consider how this information was acquired. On the basis of these discussions, what answers would you propose to the following fundamental questions? How do we know that specific genes are located on the sex-determining chromosomes rather than on autosomes?
Problem 1
- In this chapter, we focused on extensions and modifications of Mendelian principles and ratios. In the process, we encountered many opportunities to consider how this information was acquired. On the basis of these discussions, what answers would you propose to the following fundamental questions? For genes whose expression seems to be tied to the sex of individuals, how do we know whether a gene is X-linked in contrast to exhibiting sex-limited or sex-influenced inheritance?
Problem 1
- How did geneticists determine that inheritance of some phenotypic characteristics involves the interactions of two or more gene pairs? How were they able to determine how many gene pairs were involved?
Problem 1
- In this chapter, we focused on extensions and modifications of Mendelian principles and ratios. In the process, we encountered many opportunities to consider how this information was acquired. On the basis of these discussions, what answers would you propose to the following fundamental questions? How were early geneticists able to ascertain inheritance patterns that did not fit typical Mendelian ratios?
Problem 1
- Write a short essay that explains why multiple and lethal alleles often result in a modification of the classic Mendelian monohybrid and dihybrid ratios.
Problem 2
- In shorthorn cattle, coat color may be red, white, or roan. Roan is an intermediate phenotype expressed as a mixture of red and white hairs. The following data were obtained from various crosses: How is coat color inherited? What are the genotypes of parents and offspring for each cross?
Problem 3
- In foxes, two alleles of a single gene, P and p, may result in lethality (PP), platinum coat (Pp), or silver coat (pp). What ratio is obtained when platinum foxes are interbred? Is the P allele behaving dominantly or recessively in causing (a) lethality; (b) platinum coat color?
Problem 4
- In mice, a short-tailed mutant was discovered. When it was crossed to a normal long-tailed mouse, 4 offspring were short-tailed and 3 were long-tailed. Two short-tailed mice from the F1 generation were selected and crossed. They produced 6 short-tailed and 3 long-tailed mice. These genetic experiments were repeated three times with approximately the same results. What genetic ratios are illustrated? Hypothesize the mode of inheritance and diagram the crosses.
Problem 5
- List all possible genotypes for the A, B, AB, and O phenotypes. Is the mode of inheritance of the ABO blood types representative of dominance, recessiveness, or codominance?
Problem 6
- With regard to the ABO blood types in humans, determine the genotype of the male parent and female parent shown here: Male parent: Blood type B; mother type O Female parent: Blood type A; father type B Predict the blood types of the offspring that this couple may have and the expected proportion of each.
Problem 7
- In a disputed parentage case, the child is blood type O, while the mother is blood type A. What blood type would exclude a male from being the father? Would the other blood types prove that a particular male was the father?
Problem 8
Problem 9
In Drosophila subobscura, the presence of a recessive gene called grandchildless (gs) causes the offspring of homozygous females, but not those of homozygous males, to be sterile. Can you offer an explanation as to why females and not males are affected by the mutant gene?
- The A and B antigens in humans may be found in water-soluble form in secretions, including saliva, of some individuals (Se/Se and Se/se) but not in others (se/se). The population thus contains 'secretors' and 'nonsecretors.' Determine the proportion of various phenotypes (blood type and ability to secrete) in matings between individuals that are blood type AB and type O, both of whom are Se/se.
Problem 9
- The A and B antigens in humans may be found in water-soluble form in secretions, including saliva, of some individuals (Se/Se and Se/se) but not in others (se/se). The population thus contains 'secretors' and 'nonsecretors.' How will the results of such matings change if both parents are heterozygous for the gene controlling the synthesis of the H substance (Hh)?
Problem 9
- In rabbits, a series of multiple alleles controls coat color in the following way: C is dominant to all other alleles and causes full color. The chinchilla phenotype is due to the c^ch allele, which is dominant to all alleles other than C. The c^h allele, dominant only to (albino), results in the Himalayan coat color. Thus, the order of dominance is C > c^ch > c^h > c^a. For each of the following three cases, the phenotypes of the P₁ generations of two crosses are shown, as well as the phenotype of one member of the F₁ generation. For each case, determine the genotypes of the P₁ generation and the F₁ offspring, and predict the results of making each indicated cross between F₁ individuals.
Problem 11
Problem 13
In an earlier Problems and Discussion section (see Chapter 7, Problem 27), we described CC, the cat created by nuclear transfer cloning, whereby a diploid nucleus from one cell is injected into an enucleated egg cell to create an embryo. Cattle, sheep, rats, dogs, and several other species have been cloned using nuclei from somatic cells. Embryos and adults produced by this approach often show a number of different mitochondrial defects. Explain possible reasons for the prevalence of mitochondrial defects in embryos created by nuclear transfer cloning.
- Horses can be cremello (a light cream color), chestnut (a brownish color), or palomino (a golden color with white in the horse's tail and mane). Of these phenotypes, only palominos never breed true. From the results given above, determine the mode of inheritance by assigning gene symbols and indicating which genotypes yield which phenotypes.
Problem 14
- Horses can be cremello (a light cream color), chestnut (a brownish color), or palomino (a golden color with white in the horse's tail and mane). Of these phenotypes, only palominos never breed true. Predict the F₁ and F₂ results of many initial matings between cremello and chestnut horses.
Problem 14
- If you knew that a devastating late-onset inherited disease runs in your family (in other words, a disease that does not appear until later in life) and you could be tested for it at the age of 20, would you want to know whether you are a carrier? Would your answer be likely to change when you reach age 40?
Problem 15
- The genes encoding the red- and green-color-detecting proteins of the human eye are located next to one another on the X chromosome and probably evolved from a common ancestral pigment gene. The two proteins demonstrate 76 percent homology in their amino acid sequences. A normal-visioned woman (with both genes present on each of her two X chromosomes) has a red-color-blind son who was shown to have one copy of the green-detecting gene and no copies of the red-detecting gene. Devise an explanation for these observations at the chromosomal level (involving meiosis).
Problem 22
- Five human matings (1–5), identified by both maternal and paternal phenotypes for ABO and MN blood-group antigen status, are shown on the left side of the following table: Parental Phenotypes Offspring (1) A, M x A, N (a) A, N (2) B, M x B, M (b) O, N (3) O, N x B, N (c) O, MN (4) AB, M x O, N (d) B, M (5) AB, MN x AB, MN (e) B, MN Each mating resulted in one of the five offspring shown in the right-hand column (a–e). Match each offspring with one correct set of parents, using each parental set only once. Is there more than one set of correct answers?
Problem 22
- A husband and wife have normal vision, although both of their fathers are red–green color-blind, an inherited X-linked recessive condition. What is the probability that their first child will be (a) a normal son, (b) a normal daughter, (c) a color-blind son, (d) a color-blind daughter?
Problem 23
- In humans, the ABO blood type is under the control of autosomal multiple alleles. Color blindness is a recessive X-linked trait. If two parents who are both type A and have normal vision produce a son who is color-blind and is type O, what is the probability that their next child will be a female who has normal vision and is type O?
Problem 24
- In Drosophila, an X-linked recessive mutation, scalloped (sd), causes irregular wing margins. Diagram the F₁ and F₂ results if (a) a scalloped female is crossed with a normal male; (b) a scalloped male is crossed with a normal female. Compare these results with those that would be obtained if the scalloped gene were autosomal.
Problem 25
- In mice, the X-linked dominant mutation Testicular feminization (Tfm) eliminates the normal response to the testicular hormone testosterone during sexual differentiation. An XY mouse bearing the Tfm allele on the X chromosome develops testes, but no further male differentiation occurs—the external genitalia of such an animal are female. From this information, what might you conclude about the role of the Tfm gene product and the X and Y chromosomes in sex determination and sexual differentiation in mammals? Can you devise an experiment, assuming you can 'genetically engineer' the chromosomes of mice, to test and confirm your explanation?
Problem 26
- In Drosophila, the X-linked recessive mutation vermilion (v) causes bright red eyes, in contrast to the brick-red eyes of wild type. A separate autosomal recessive mutation, suppressor of vermilion (su-v), causes flies homozygous or hemizygous for v to have wild-type eyes. In the absence of vermilion alleles, su-v has no effect on eye color. Determine the F₁ and F₂ phenotypic ratios from a cross between a female with wild-type alleles at the vermilion locus, but who is homozygous for su-v, with a vermilion male who has wild-type alleles at the su-v locus.
Problem 27
- When the cloned cat Carbon Copy (CC) was born (see the Now Solve This question in Section 7.4), she had black patches and white patches, but completely lacked any orange patches. The knowledgeable students of genetics were not surprised at this outcome. Starting with the somatic ovarian cell used as the source of the nucleus in the cloning process, explain how this outcome occurred.
Problem 27
- While vermilion is X-linked in Drosophila and causes the eye color to be bright red, brown is an autosomal recessive mutation that causes the eye to be brown. Flies carrying both mutations lose all pigmentation and are white-eyed. Predict the F₁ and F₂ results of the following crosses: vermilion females x brown males
Problem 28
- While vermilion is X-linked in Drosophila and causes the eye color to be bright red, brown is an autosomal recessive mutation that causes the eye to be brown. Flies carrying both mutations lose all pigmentation and are white-eyed. Predict the F₁ and F₂ results of the following crosses: brown females x vermilion males
Problem 28
- While vermilion is X-linked in Drosophila and causes the eye color to be bright red, brown is an autosomal recessive mutation that causes the eye to be brown. Flies carrying both mutations lose all pigmentation and are white-eyed. Predict the F₁ and F₂ results of the following crosses: white females x wild-type males
Problem 28
