Patterns of Inheritance Practice Test (page 3)

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By — McGraw-Hill Professional
Updated on Aug 19, 2011

Modified Dihybrid Ratios Questions

  1. In peaches, the homozygous genotype GOGO produces oval glands at the base of the leaves, the heterozygous genotype GOGA produces round glands, and the homozygous genotype GAGA results in the absence of glands. At another locus, a dominant gene S produces fuzzy peach skin and its recessive allele s produces smooth (nectarine) skin. A homozygous variety with oval glands and smooth skin is crossed to a homozygous variety with fuzzy skin and lacking glands at the base of its leaves. What genotypic and phenotypic proportions are expected in the F2?
  2. In Shorthorn cattle, coat colors are governed by a codominant pair of alleles CR and CW. The homozygous genotype CRCR produces red, the other homozygote produces white, and the heterozygote produces roan (a mixture of red and white). The presence of horns is produced by the homozygous recessive genotype pp and the polled condition by its dominant allele P. If roan cows heterozygous for the horned gene are mated to a horned, roan bull, what phenotypic ratio is expected in the offspring?
  3. A gene locus with codominant alleles is known to govern feather color in chickens such that the genotype FBFB = black, FWFW =splashed white, and FBFW = blue. Another locus with codominant alleles governs feather morphology such that MNMN = normal feather shape, MNMF = slightly abnormal feathers called "mild frizzle," and MFMF = grossly abnormal feathers called "extreme frizzle." If blue, mildly frizzled birds are crossed among themselves, what phenotypic proportions are expected among their offspring?
  4. In the above problem, if all the blue offspring with normal feathers and all the splashed-white, extremely frizzled offspring are isolated and allowed to mate at random, what phenotypic ratio would be expected among their progeny?
  5. The shape of radishes may be long (LL), round (L'L'), or oval (LL'). Color may be red (RR), white (R'R'), or purple (RR'). If a long, white strain is crossed with a round, red strain, what phenotypic proportions are expected in the F1 and F2?
  6. Suppose that two strains of radishes are crossed (see the above problem) and produce a progeny consisting of 16 long white, 31 oval purple, 16 oval white, 15 long red, 17 oval red, and 32 long purple. What would be the phenotypes of the parental strains?
  7. A dominant gene K in mice produces a kinked tail; recessive genotypes at this locus kk have normal tails. The homozygous condition of another locus AA produces a gray color called agouti; the heterozygous condition AyA produces yellow color; the homozygous genotype AyAy is lethal. (a) If yellow mice, heterozygous for kinky tail, are crossed together, what phenotypic proportions are expected in their offspring? (b) What proportion of the offspring is expected to be of genotype AyAKk? (c) If all the yellow offspring were allowed to mate at random, what would be the genotypic and phenotypic ratios among their adult progeny?
  8. An incompletely dominant gene N in the Romney Marsh breed of sheep causes the fleece of homozygotes to be "hairy," i.e., containing fibers lacking the normal amount of crimp. Normal wool is produced by the homozygous genotype N'N'. Heterozygotes NN' can be distinguished at birth by the presence of large, medulated fibers called "halo-hairs" scattered over the body. A gene known as "lethal gray" causes homozygous gray fetuses (GlGl) to die before 15 weeks in gestation. The heterozygous genotype G1G produces gray fleece, and the homozygous genotype GG produces black. If heterozygous halo-haired, gray individuals are mated together, (a) what would be the phenotypic proportions expected in the live progeny, (b) what proportion of the live progeny would carry the lethal gene, (c) what proportion of the live progeny with halo-hairs would carry the lethal gene, (d) what proportion of all the zygotes would be expected to be of genotype NN'GlGl?
  9. Tay-Sachs disease is a recessive hereditary abnormality in humans causing death within the first few years of life only when homozygous (ii). The dominant condition at this locus produces a normal phenotype (I-). Abnormally shortened fingers (brachyphalangy) is thought to be due to a genotype heterozygous for a lethal gene (BBL), the homozygote (BB>) being normal, and the other homozygote (BLBL) being lethal. What are the phenotypic expectations among teenage children from parents who are both brachyphalangic and heterozygous for Tay-Sachs disease?
  10. In addition to the gene governing Tay-Sachs disease in the above problem, the recessive genotype of another locus (jj) results in death before age 18 due to a condition called Spielmeyer-Vogt disease. Only individuals of genotype I- J will survive to adulthood, (a) What proportion of the children from parents of genotype IiJj would probably not survive to adulthood? (b) What proportion of the adult survivors in part (a) would not be carriers of either hereditary abnormality'?
  11. A genetic condition on chromosome 2 in the fruit fly Drosophila melanogaster is lethal when homozygous (Pm/Pm), but when heterozygous (Pm/Pm+) produces a purplish eye color called "plum." The other homozygous condition (Pm+/Pm+) produces wild-type eye color. On chromosome 3, a gene called "stubble" produces short, thick bristles when heterozygous (Sb/Sb+) but is lethal when homozygous (Sb/Sb). The homozygous condition of its alternative allele (Sb+/Sb+), produces bristles of normal size (wild type). (a) What phenotypic ratio is expected among progeny from crosses between plum, stubble parents? (b) If the offspring of part (a) are allowed to mate at random to produce an F2, what phenotypic ratio is expected?
  12. Feather color in chickens is governed by a pair of codominant alleles such that FBFB produces black, FWFW produces splashed white, and FBFW produces blue. An independently segregating locus governs the length of leg; CC genotypes possess normal leg length, CCL genotypes produce squatty, short-legged types called "creepers," but homozygous CLCL genotypes are lethal. Determine the kinds of progeny phenotypes and their expected ratios that crosses between dihybrid blue creepers are likely to produce.

Higher Combinations Questions

  1. The seeds from Mendel's tall plants were round and yellow, all three characters due to a dominant gene at each of three independently assorting loci. The recessive genotypes dd, ww, and gg produce dwarf plants with wrinkled and green seeds, respectively. (a) If a pure tall, wrinkled, yellow variety is crossed with a pure dwarf, round, green variety, what phenotypic ratio is expected in the F1 and F2? (b) What percentage of the F2 is expected to be of genotype DdWWgg? (c) If all the dwarf, round, green individuals in the F2 are isolated and artificially crossed at random, what phenotypic ratio of offspring is expected?
  2. The coat colors of mice are known to be regulated by several genes. The presence of a yellow band of pigment near the tip of the hair is called "agouti" pattern and is produced by the dominant allele A. The recessive condition at this locus (aa) does not have this subapical band and is termed nonagouti. The dominant allele of another locus B produces black and the recessive genotype bb produces brown. The homozygous genotype chch restricts pigment production to the extremities in a pattern called Himalayan, whereas the genotype C- allows pigment to be distributed over the entire body. (a) In crosses between pure brown, agouti, Himalayan, and pure black mice, what are the phenotypic expectations of the F1 and F2? (b) What proportion of the black-agouti, full-colored F2 would be expected to be of genotype AaBBCc? (c) What percentage of all the Himalayans in the F2 would be expected to show brown pigment? (d) What percentage of all the agoutis in the F2 would be expected to exhibit black pigment?
  3. In addition to the information given in the problem above, a fourth locus in mice is known to govern the density of pigment deposition. The genotype D- produces full color, but the recessive genotype dd produces a dilution of pigment. Another allele at this locus, dl is lethal when homozygous, produces a dilution of pigment in the genotype ddl, and produces full color when in heterozygous condition with the dominant allele Ddl. (a) What phenotypic ratio would be expected among the live F2 progeny if the F1 from the cross aabbCCDd × AABBccddl were allowed to mate at random? (b) What proportion of the live F2 would be expected to be of genotype AABbccddl?
  4. In the parental cross AABBCCDDEE × aabbccddee, (a) how many different F1 gametes can be formed, (b) how many different genotypes are expected in the F2, (c) how many squares of a Punnett square would be necessary to accommodate the F2?
  5. A pure strain of Mendel's peas, dominant for all seven of his independently assorting genes, was testcrossed. (a) How many different kinds of gametes could each of the parents produce? (b) How many different gametes could the F1 produce? (c) If the F1 was testcrossed, how many phenotypes would be expected in the offspring and in what proportions? (d) How many genotypes would be expected in the F2? (e) How many combinations of F1 gametes are theoretically possible (considering, e.g., AABBCCDDEEFFGG sperm nucleus × aabbccddeeffgg egg nucleus, a different combination than AABBCCDDEEFFGG egg nucleus × aabbccddeeffgg sperm nucleus)? ( f ) How many different kinds of matings could theoretically be made among the F2? [Hint: See solution to Problem 2.14(c)].

Testing Genetic Ratios Questions

  1. Determine the number of degrees of freedom when testing the ratios (a) 3 : 1 (b) 9 : 3 : 3 :1 (c) 1 : 2 : 1 (d ) 9 :3 : 4. Find the number of degrees of freedom in applying a chi-square test to the results from (e) testcrossing a dihybrid, ( f ) testcrossing a trihybrid, (g) trihybrid × trihybrid cross.
  2. Two phenotypes appear in an experiment in the ratio 16 : 4. (a) How well does this sample fit a 3 : 1 ratio? Would a sample with the same proportional deviation fit a 3 : 1 ratio if it were (b) 10 times larger than (a), (c) 20 times larger than (a)?
  3. The flowers of four o'clock plants may be red, pink, or white. Reds crossed to whites produced only pink offspring. When pink-flowered plants were crossed they produced 113 red, 129 white, and 242 pink. It is hypothesized that these colors are produced by a single-gene locus with codominant alleles. Is this hypothesis acceptable on the basis of a chisquare test?
  4. A heterozygous genetic condition called "creeper" in chickens produces shortened and deformed legs and wings, giving the bird a squatty appearance. Matings between creepers produced 775 creeper : 388 normal progeny. (a) Is the hypothesis of a 3 : 1 ratio acceptable? (b) Does a 2 : 1 ratio fit the data better? (c) What phenotype is probably produced by the gene for creeper when in homozygous condition?
  5. Among fraternal (nonidentical, dizygotic) twins, the expected sex ratio is 1MM: 2MF : 1 FF (M = male, F = female). A sample from a sheep population contained 50 MM, 142 MF, and 61 FF twin pairs. (a) Do the data conform within statistically acceptable limits to the expectations? (b) If identical (monozygotic) twin pairs = total pairs × (2 × MF pairs), what do the data indicate concerning the frequency of monozygotic sheep twins?
  6. A total of 320 families with six children each were surveyed with the results shown below. Does this distribution indicate that boys and girls are occurring with equal frequency?
  7. In guinea pigs, it is hypothesized that a dominant allele L governs short hair and its recessive allele l governs long hair. Codominant alleles at an independently assorting locus are assumed to govern hair color, such that CyCy = yellow, CyCw = cream, and CwCw = white. From the cross Ll CyCw × Ll CyCw, the following progeny were obtained: 50 short cream : 21 short yellow : 23 short white : 21 long cream : 7 long yellow : 6 long white. Are the data consistent with the genetic hypothesis?
  8. Observations of 30 : 3 in a genetic experiment are postulated to be in conformity with a 3 : 1 ratio. Is a 3 : 1 ratio acceptable at the 5% level on the basis of (a) an uncorrected chi-square test, (b) a corrected chi-square test? [Hint: Corrected indicates use of Yates correction factor of continuity.]

Pedigree Analysis Questions

  1. The phenotypic expression of a dominant gene in Ayrshire cattle is a notch in the tips of the ears. In the pedigree below, where solid symbols represent notched individuals, determine the probability of notched progeny being produced from the matings (a) III1 × III3 (b) III2 × III3 (c) III3 × III4 (d) III1 × III5 (e) III2 × III5
  2. A multiple allelic series in dogs governs the distribution of coat-color pigments. The allele As produces an even distribution of dark pigment over the body; the allele ay reduces the intensity of pigmentation and produces sable or tan-colored dogs; the allele at produces spotted patterns such as tan and black, tan and brown, etc. The dominance hierarchy is As > ay > at. Given the following family pedigree, (a) determine the genotypes of all the individuals insofar as possible, (b) calculate the probability of spotted offspring being produced by mating III1 by III2, (c) find the fraction of the dark-pigmented offspring from I1 × III3 that is expected to be heterozygous.
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