Genetic Interactions Practice Test (page 4)

Review the following concepts if needed:

• Two-Factor Interactions for Genetics
• Epistatic Interactions for Genetics
• Pedigree Analysis for Genetics
• Nonepistatic Interactions and Pleiotropism for Genetics

Genetic Interactions Practice Test

Matching Questions

Match the expected phenotypic ratios (right column) in progeny from dihybrid parents with the conditions specified in the left column.

Vocabulary Questions

For each of the following definitions, give the appropriate term and spell it correctly

1. Protein catalysts that speed the rate of chemical reactions.
2. The material(s) acted upon and changed by the catalyst in question 1.
3. The phenomenon in which a specific genotype(s) at one locus can prevent the phenotypic manifestation of a genotype (s) at one or more other loci.
4. Adjective describing a locus whose phenotypic manifestation is suppressed by the phenomenon in question 3.
5. A phenomenon wherein a single gene has more than one phenotypic effect.
6. A collection of phenotypic effects that collectively defines a disease, genetic or otherwise.

Multiple-Choice Questions

Questions1–5 use the information in the diagram below.

1. The genotype(s) capable of making C is/are     (g) G¹g¹G²g²     (h) G¹G¹g²g²     (i) G¹g¹g²g²     (j) g¹g¹G²G²     (k) more than one of the above
2. In a cross between genotypes g¹g¹G²G² × G¹G¹g²g² what fraction of the F₂ is expected to be phenotypically B-positive and C-negative?     (a) 1/16     (b) 3/16     (c) 3/8     (d) 1/4     (e) none of the above
3. What fraction of the F₂ in the above cross (question 2) is expected to be C-negative?     (a) 3/4     (b) 1/2     (c) 9/16     (d) 7/16     (e) none of the above
4. What fraction of the F₂ (in question 2) is expected to be able to make enzyme 2, but not enzyme 1?     (a) 3/4     (b) 3/16     (c) 9/16     (d) 3/8     (e) none of the above
5. If a dihybrid is testcrossed, what fraction of the progeny is expected to be able to make substance C?     (a) 9/16     (b) 3/16     (c) 3/8     (d) 1/4     (e) none of the above

Questions 6–10 use the information in the following diagram. Enzyme e₃ becomes inactivated by binding to substance P.



6. If the phenotype is determined by the presence or absence of substance N, what type of interaction exists?     (a) dominant and recessive     (b) duplicate recessive     (c) duplicate dominant     (d) duplicate genes with cumulative action     (e) none of the above
7. Approximately (within rounding error) what percentage of the F₁ from G³g³G⁴g⁴ parents is expected to be N-positive?     (a) 56     (b) 19     (c) 25     (d) 38     (e) none of the above
8. When dihybrids are testcrossed, the percentage of their progeny expected to be N-negative is     (a) 25     (b) 81     (c) 75     (d) 38     (e) none of the above
9. Among the N-positive progeny from dihybrid parents, what fraction is expected to be P-positive?     (a) 3/4     (b) 1/2     (c) 2/3     (d) 5/6     (e) none of the above
10. What fraction of the progeny from dihybrid parents is expected to be P-positive and N-negative?     (a) 9/16     (b) 7/16     (c) 6/16     (d) 3/4     (e) none of the above

Two-Factor Interactions Questions

1. When homozygous yellow rats are crossed to homozygous black rats, the F₁ is all gray. Mating the F₁ among themselves produced an F₂ consisting of 10 yellow, 28 gray, 2 cream-colored, and 8 black.     (a) How are these colors inherited?     (b) Show, using appropriate genetic symbols, the genotypes for each color. (c) How many of the 48 F₂ rats were expected to be cream-colored?     (d) How many of the 48 F₂ rats were expected to be homozygous?
2. Four comb shapes in poultry are known to be governed by two gene loci. The genotype R-P-produces walnut comb, characteristic of the Malay breed; R-pp produces rose comb, characteristic of the Wyandotte breed; rrP- produces pea comb, characteristic of the Brahma breed; rrpp produces single comb, characteristic of the Leghorn breed.     (a) If pure Wyandottes are crossed with pure Brahmas, what phenotypic ratios are expected in the F₁ and F₂?     (b) A Malay hen was crossed to a Leghorn cock and produced a dozen eggs, three of which grew into birds with rose combs and nine with walnut combs. What is the probable genotype of the hen? (c) Determine the proportion of comb types that would be expected in offspring from each of the following crosses: (1) Rrpp × RrPP (2) rrPp × RrPp (3) rrPP × RRPp (4) RrPp × rrpp (5) RrPp × RRpp (6) RRpp × rrpp (7) RRPP × rrpp (8) Rrpp × Rrpp (9) rrPp × Rrpp (10) rrPp × rrpp.
3. Listed below are 7 two-factor interaction ratios observed in progeny from various dihybrid parents. Suppose that in each case one of the dihybrid parents is testcrossed (instead of being mated to another dihybrid individual). What phenotypic ratio is expected in the progeny of each testcross?     (a) 9 : 6: 1    (b) 9 : 3: 4     (c) 9 : 7     (d) 15:1     (e) 12 : 3 : 1     (f) 9 : 3 : 3 : 1     (g) 13 : 3.
4. White fruit color in summer squash is governed by a dominant gene W and colored fruit by its recessive allele w. Yellow fruit is governed by an independently assorting hypostatic gene G and green by its recessive allele g. When dihybrid plants are crossed, the offspring appear in the ratio 12white : 3 yellow: 1 green. What fruit color ratios are expected from the following crosses:     (a) Wwgg × WwGG     (b) WwGg × green (c) Wwgg × wwGg     (d) WwGg × Wwgg?     (e) If two plants are crossed producing 1/2 yellow and 1/2 green progeny, what are the genotypes and phenotypes of the parents?
5. The Black Langshan breed of chickens has feathered shanks. When Langshans are crossed to the Buff Rock breed with unfeathered shanks, all the F₁ have feathered shanks. Out of 360 F₂ progeny, 24 were found to have nonfeathered shanks and 336 had feathered shanks.     (a) What is the mode of interaction in this trait?     (b) What proportion of the feathered F₂ would be expected to be heterozygous at one locus and homozygous at the other?
6. On chromosome 3 of corn there is a dominant gene A₁, which, together with the dominant gene (A₂) on chromosome 9, produces colored aleurone. All other genetic combinations produce colorless aleurone. Two pure colorless strains are crossed to produce an all-colored F₁.     (a) What were the genotypes of the parental strains and the F₁?     (b) What phenotypic proportions are expected among the F₂?     (c) What genotypic ratio, exists among the white F₂?
7. Two pairs of alleles govern the color of onion bulbs. Apure-red strain crossed to a pure-white strain produces an all-red F₁. The F₂ was found to consist of 47 white, 38 yellow, and 109 red bulbs.    (a) What epistatic ratio is approximated by the data?     (b) What is the name of this type of gene interaction?     (c) If another F₂ is produced by the same kind of a cross, and eight bulbs of the F₂ are found to be of the double-recessive genotype, how many bulbs would be expected in each phenotypic class?
8. The color of corn aleurone is known to be controlled by several genes; A, C, and R are all necessary for color to be produced. The locus of a dominant inhibitor of aleurone color, I, is very closely linked to that of C. Thus, any one or more of the genotypes I-, aa-, cc-, or rr- produces colorless aleurone.     (a) What would be the colored : colorless ratio among F₂ progeny from the cross AAIICCRR × aaiiCCRR?     (b) What proportion of the colorless F₂ is expected to be homozygous?
9. Suppose that crossing two homozygous lines of white clover, each with a low content of cyanide, produces only progeny with high levels of cyanide. When these F₁ progeny are backcrossed to either parental line, half the progeny has low cyanide content and the other half has high cyanide content.     (a) What type of interaction may account for these results?     (b) What phenotypic ratio is expected in the F₂?     (c) If a 12 : 4 ratio is observed among progeny from parents with high cyanide content, what are the parental genotypes?     (d) If the low cyanide F₂, exclusive of the double recessives, are allowed to cross at random among them-selves, what proportion of their progeny is expected to contain a high cyanide content?
10. In cultivated flowers called "stocks," the recessive genotype of one locus (aa) prevents the development of pigment in the flower, thus producing a white color. In the presence of the dominant allele A, alleles at another locus may be expressed as follows: C- = red, cc = cream. (a) When cream stocks of the genotype Aacc are crossed to red stocks of the genotype AaCc, what phenotypic and genotypic proportions are expected in the progeny?     (b) If cream stocks crossed to red stocks produce white progeny, what may be the genotypes of the parents?     (c) When dihybrid red stocks are crossed together, what phenotypic ratio is expected among the progeny?     (d) If red stocks crossed to white stocks produce progeny with red, cream, and white flowers, what are the genotypes of the parents?
11. An inhibitor of pigment production in onion bulbs (I-) exhibits dominant epistasis over another locus, the genotype iiR- producing red bulbs and iirr producing yellow bulbs.     (a) A pure-white strain is crossed to a purered strain and produces an all-white F₁ and an F₂ with 12/16 white, 3/16 red, and 1/16 yellow. What were the genotypes of the parents?     (b) If yellow onions are crossed to a pure-white strain of a genotype different from the parental type in part (a), what phenotypic ratio is expected in the F₁ and F₂?     (c) Among the white F₂ of part (a), suppose that 32 were found to be of genotype IiRR. How many progeny are expected in each of the three F₂ phenotypic classes?
12. The color of the flower center in the common yellow daisy may be either purple-centered or yellow-centered. Two genes (P and Y) are known to interact in this trait. The results of two matings are given below:
    

Determine the phenotypic ratios of progeny from the matings     (a) PpYy × PpYy     (b) PpYy × ppyy     (c) PPyy × ppYY.

13. The aleurone of corn kernels may be either yellow, white, or purple. When pollen from a homozygous purple plant is used to fertilize a homozygous white plant, the aleurones of the resulting kernels are all purple. When homozygous yellow plants are crossed to homozygous white plants, only seeds with yellow aleurone are produced. When homozygous purple plants are crossed to homozygous yellow plants, only purple progeny appear. Some crosses between purple plants produce purple, yellow, and white progeny. Some crosses between yellow plants produce both yellow and white offspring. Crosses between yellow plants never produce purple progeny. Crosses among plants produced from seeds with white aleurone always produce only white progeny.     (a) Can these results be explained on the basis of the action of a single-gene locus with multiple alleles?     (b) What is the simplest explanation for the mode of gene action?     (c) If plants with only dominant alleles at the two loci are crossed to plants grown from white seeds, what phenotypic proportions are expected among their F₂ progeny?     (d) In part (c), how many generations of seeds must be planted in order to obtain an F₂ progeny phenotypically expressing the aleurone genes derived from the adult parent sporophytes?     (e) What is the advantage of studying the genetics of seed traits rather than traits of the sporophyte?
14. Three fruit shapes are recognized in the summer squash (Cucurbita pepo): disk-shaped, elongated, and sphere shaped. Apure disk-shaped variety was crossed to a pure elongated variety. The F₁ were all disk-shaped. Among 80 F₂, there were 30 sphere-shaped, 5 elongated, and 45 disk-shaped.     (a) Reduce the F₂ numbers to their lowest ratio.     (b) What types of interaction is operative?     (c) If the sphere-shaped F₂ cross at random, what phenotypic proportions are expected in the progeny?

Pedigree Analysis Questions

15. The pedigree below illustrates a case of dominant epistasis.     (a) What symbol represents the genotype A-B-?     (b) What symbol represents the genotype aaB-?     (c) What symbol represents the genotype aabb?     (d) What type of epistasis would be represented if II2 &215; II3 produced, in addition to ❏ and , an offspring of type ?     (e) What type of interaction would be represented if III5 × III6 produced, in addition to and Ο, an offspring of type .?



16. Given the following pedigree showing three generations of mink breeding, where open symbols represent wild type and solid symbols represent platinum, determine     (a) the mode of inheritance of these coat colors,     (b) the most probable genotypes of all individuals in the pedigree (use of familiar symbols such as A, a and B, b are suitable),     (c) what phenotypic proportions are expected in progeny from III1 × III2.



17. The pedigree below shows the genetic transmission of feather color in chickens. Open symbols represent white feathers, solid symbols represent colored feathers. Under the assumption of dominant and recessive interaction (given A- or bb or both = white, aaB- = color), assign genotypes to each individual in the pedigree. Indicate by (-) whatever genes cannot be determined.

Interactions with Three or More Factors Questions

18. A wheat variety with colored seeds is crossed to a colorless strain producing an all-colored F₁. In the F₂, 1/64 of the progeny has colorless seeds.     (a) How many pairs of genes control seed color?     (b) What were the genotypes of the parents and the F₁ (use your own symbols)?
19. In mice, spotted coat color is due to a recessive gene s and solid coat color to its dominant allele S. Colored mice possess a dominant allele C whereas albinos are homozygous recessive cc. Black is produced by a dominant allele B and brown by its recessive allele b. The cc genotype is epistatic to both the B and S loci. What phenotypic ratio is expected among the progeny of trihybrid parents?
20. A pure line of corn (CCRR) exhibiting colored aleurone is testcrossed to a colorless aleurone strain. Approximately 56% of the F₂ has colored aleurone, the other 44% being colorless. A pure line (AARR) with colored aleurone, when testcrossed, also produces the same phenotypic ratio in the F₂.     (a) What phenotypic ratio is expected in the F₂ when a pure-colored line of genotype AACCRR is testcrossed?     (b) What proportion of the colorless F₂ is aaccrr?     (c) What genotypic ratio exists among the colored F₂?
21. If a pure-white onion strain is crossed to a pure-yellow strain, the F₂ ratio is 12 white: 3 red: 1 yellow. If another pure white onion is crossed to a pure-red onion, the F₂ ratio is 9 red : 3 yellow : 4 white.     (a) What percentage of the white F₂ from the second mating would be homozygous for the yellow allele?     (b) If the white F₂ (homozygous for the yellow allele) of part (a) is crossed to the pure-white parent of the first mating mentioned at the beginning of this problem, determine the F₁ and F₂ phenotypic expectations.
22. For any color to be developed in the aleurone layer of corn kernels, the dominant alleles at two loci plus the recessive condition at a third locus (A-R-ii) must be present. Any other genotypes produce colorless aleurone.     (a) What phenotypic ratio of colored : colorless would be expected in progeny from matings between parental plants of genotype AaRrli?     (b) What proportion of the colorless progeny in part (a) would be expected to be heterozygous at one or more of the three loci?    (c) What is the probability of picking from among the colored seeds in part (a) two seeds that, when grown into adult sporophytes and artificially crossed, would produce some colorless progeny with the triple-recessive genotype?
23. A dominant gene V in humans causes certain areas of the skin to become depigmented, a condition called "vitiligo." Albinism is the complete lack of pigment production and is produced by the recessive genotype aa. The albino locus is epistatic to the vitiligo locus. Another gene locus, the action of which is independent of the previously mentioned loci, is known to be involved in a mildly anemic condition called "thalassemia."     (a) When the adult progeny from parents both of whom exhibit vitiligo and a mild anemia is examined, the following phenotypic proportions are observed : 1/16 normal : 3/16 vitiligo : 1/8 mildly anemic : 1/12 albino : 3/8 vitiligo and mildly anemic : 1/6 albino and mildly anemic. What is the mode of genetic action of the gene for thalassemia?     (b) What percentage of the viable albino offspring in part (a) would carry the gene for vitiligo?     (c) What percentage of viable offspring with symptoms of mild anemia also show vitiligo?
24. When the White Leghorn breed of chickens is crossed to the White Wyandotte breed, all the F₁ birds have white feathers. The F₂ birds appear in the ratio 13 white : 3 colored. When the White Leghorn breed is crossed to the White Silkie breed, the F₁ is white and the F₂ is also 13 white : 3 colored. But when White Wyandottes are crossed to White Silkies, the F₁ is all colored and the F₂ appears in the ratio 9 colored : 7white.     (a) Howare feather colors inherited in these breeds (use appropriate symbols in your explanation)?     (b) Show, by use of your own symbols, the genotypes of each of the three breeds (assume the breed is homozygous for all loci under consideration).     (c) What phenotypic ratio is expected among progeny from trihybrid parents?     (d) What proportion of the white offspring of part (c) is expected to be dihybrid?

Answers

Matching

1. E   2. C   3. A   4. F   5. G   6. D   7. B

Vocabulary

1. enzymes 2. substrate(s) 3. epistasis 4. hypostatic 5. pleiotropism 6. syndrome

Multiple-Choice

1. a
2. b
3. d
4. b
5. d
6. a
7. b
8. c
9. a (zero)
10. d

Two-Factor Interactions

1. (a) Two pairs of nonepistatic genes interact to produce these coat colors.     (b) A-B- (gray), A-bb (yellow), aaB- (black), aabb (cream)     (c) 3     (d) 12
2. (a) F₁: all walnut comb; F₂: 9/16 walnut : 3/16 rose : 3/16 pea : 1/16 single     (b) RRPp

    (c)

3. (a) 1 : 2 : 1     (b) 1 : 1 : 2     (c) 1 : 3     (d) 3 : 1     (e) 2 : 1 : 1     (e) 1 : 1 : 1 : 1     (g) 3 : 1
4. (a) 3/4 white : 1/4 yellow     (b) and     (c) 1/2 white : 1/4 yellow : 1/4 green     (d) 3/4 white : 1/8 yellow : 1/8 green     (e) yellow (wwGg) × green (wwgg)
5. (a) Duplicate dominant genes with only the double-recessive genotype producing nonfeathered shanks     (b) 8/15
6. (a) P : A₁A₁a₂a₂ × a₁a₁A₂A₂; F₁: A₁a₁A₂a₂;     (b) 9/16 colored : 7/16 colorless     (c) 1/7 A₁A₁a₂a₂ : 2/7 A₁a₁a₂a₂ : 1/7 a₁a₁A₂A₂ : 2/7 a₁a₁A₂a₂ : 1/7 a₁a₁a₂a₂
7. (a) 9 : 3 : 4     (b) Recessive epistasis     (c) 32 white : 24 yellow : 72 red
8. (a) 13 colorless : 3 colored     (b) 3/13
9. (a) Duplicate recessive interaction     (b) 9 high cyanide : 7 lowcyanide     (c) A-Bb × AABb or AaB- × AaBB     (d) 2/9
10. (a) 3/8 red : 3/8 cream : 1/4 white : 1/8 AACc : 1/8 AAcc : 1/4 AaCc : 1/4 Aacc : 1/8 aaCc : 1/8 aacc     (b) Aacc × AaCc (or) Aacc × AaCC     (c) 9 red : 3 cream : 4 white     (d) AaCc × aaCc (or) AaCc × aacc
11. (a) IIrr × iiRR     (b) F₁: all white : F₂: 12/16 white : 3/16 red : 1/16 yellow     (c) 16 yellow : 48 red : 192 white
12. (a) 9/16 purple-centered : 7/16 yellow-centered     (b) 1/4 purple-centered : 3/4 yellow-centered     (c) All purplecentered
13. (a) No     (b) Dominant epistasis where Y-R- or yyR- produce purple, Y-rr = yellow, and yyrr = white     (c) 3/4 purple : 3/16 yellow : 1/16 white     (d) One     (e) The appearance of seed traits requires one less generation of rearing than that for tissues found in the sporophyte.
14. (a) 9 disk : 6 sphere : 1 elongated     (b) Duplicate genes with cumulative effect     (c) 2/3 sphere : 2/9 disk : 1/9 elongate