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Genetics Problem Set 3A
Genetics Problem Set 3B
Last Updated 3/15/06
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Genetics Problem Set 3C -- Gene-Gene Interactions

True/False, Multiple Choice, Matching etc.
1) Which are the TRUE statements below.
A) Expressivity is a measure of the intensity of a trait. B) Most complementary loci are genes which code for enzymes in the same metabolic pathway. C) Penetrance and expressivity are the same thing. D) Duplicate genes are two or more gene loci with similar sets of alleles. E) Penetrance is a measure of the intensity of a phenotypes expression. F) Codominant alleles produce the traits of both alleles when heterozygous. G) Epistasis is an example of the interaction between two gene loci. H) Complementation is an example of the interaction between two or more gene loci.

2) Match the term on the left with the BEST term on the right (You may use each answer more than once).

___1) Phenotypic ratio for a dihybrid cross with duplicate genes ..................................... A) 2:1
___2) Genotypic ratio of a monohybrid cross (without lethal alleles) ............................... B) 2:2:1
___3) One possible phenotypic ratio of a monohybrid cross with a recessive lethal allele C) 9:7
___4) Phenotypic ratio of a testcross with a monohybrid ................................................ D) 9:3:3:1
___5) Phenotypic ratio of a monohybrid cross with incomplete dominance ..................... E) 1:1
___6) Phenotypic ratio of a dihybrid cross with complementary genes ............................ F) 1:1:1:1
___7) Phenotypic ratio of a dihybrid cross with dominant epistasis ................................. G) 12:3:1
___8) Phenotypic ratio of a dihybrid cross with recessive epistasis ................................. H) 9:3:4
___9) Phenotypic ratio of a testcross with a dihybrid ........................................................ I) 15:1
.......................................................................................................................................... J) 1:2:1
......................................................................................................................................... K) 3:1
......................................................................................................................................... L) 9:6:1

3) __________ catalyze the chemical reactions in living things.
A) Structural proteins ... B) Hormones ... C) Enzymes ... D) Histones ... E) DNA

Genetics Problems (Crosses)
1) In Ground hogs the allele E for the ability to see shadows is dominant to the allele e for the inability to see shadows. The dominant allele H causes groundhogs to hide from shadows that they see. If a heterozygous shadow seeing and hiding male is crossed with a heterozygous seeing female who doesn't hide, what expected proportion of their progeny will hide from shadows?

2) In eggplant the allele c+ is needed for flower and petiole color expression while the allele c- results in no color, that is, white flowers and green petioles. The allele Gr for dark green leaf blades is dominant to the allele gr for light green leaf blades, and the allele p+ for purple petioles is dominant to the allele p- for green petioles? What is the expected phenotypic ratio of a cross between eggplants of the genotypes c+c- grgr p-p- X c+c- Grgr p+p- if the three loci are not linked?

Genetics Problems (Mode of Inheritance)
1) Dr. G.C. Wobble is crossing two pure breeding lines of flies. One line has stubby clear wings and the other has large dark brown wings. The F1 all have stubby clear wings. The F2 flies have the phenotypes in the table below.

Phenotype [Number of flies]
Stubby Clear Wings [230], Large Brown Wings [70], Large Tan Wings [25]

Propose a mode of inheritance (hypothesis) for the results shown above?

2) Dr. Woody Dicot is crossing two pure breeding lines of shrubs. One line has red leaves and the other has green leaves. The F1 all have green leaves with white flecks. The F2 seedlings have the phenotypes in the table below. The alleles segregate independently at each locus.

Phenotype [Number of plants]
Red leaves [63], Green leaves [44], Green leaves with white flecks [123]

Propose a mode of inheritance (hypothesis) for the results shown above?

3) Dinosaurs were found in the pine barrens of New Jersey by Dr. Rock Fossil. In this Triceratops species, a strain with short black feathers is crossed with a strain covered with long brown feathers (this is not an easy thing to do). The following phenotypes were seen in the F2 generation.

Phenotype [Number]
Short black feathers [118], Long brown feathers [12], Long tan feathers [33]

A) What is the most likely mode of inheritance for these traits? B) What was (were) the phenotypes of the F1 generation? C) A short feathered male, with one long brown feathered parent and another parent from a line with only black and tan feathers, is crossed with a female heterozygous for all loci involved in feather traits. What is the expected phenotypic ratios of the progeny? 

 ====================== ANSWERS ====================

True/False, Multiple Choice, Matching etc.
1) True statements below.
A) Expressivity is a measure of the intensity of a trait. B) Most complementary loci are genes which code for enzymes in the same metabolic pathway. D) Duplicate genes are two or more gene loci with similar sets of alleles. F) Codominant alleles produce the traits of both alleles when heterozygous. G) Epistasis is an example of the interaction between two gene loci. H) Complementation is an example of the interaction between two or more gene loci.

2)
1) I) 15:1
2) J) 1:2:1
3) A) 2:1
4) E) 1:1
5) J) 1:2:1
6) C) 9:7
7) G) 12:3:1
8) H) 9:3:4
9) F) 1:1:1:1

3) C) enzymes

Genetics Problems (Crosses)
1) E_ Sees shadows ee Does not see shadows
H_ Hides from shadows it sees hh Does not hide from shadows it sees
Cross: Ee Hh X Ee hh

Hide from shadows = E_ H_ [These see the shadows and hide from them (complementary loci)] = 3/4 X 1/2 = 3/8

2) In eggplant the allele c+ is needed for flower and petiole color expression while the allele c- results in no color, that is, white flowers and green petioles. The allele Gr for dark green leaf blades is dominant to the allele gr for light green leaf blades, and the allele p+ for purple petioles is dominant to the allele p+ for green petioles? What is the expected phenotypic ratio of a cross between eggplants of the genotypes c+c- grgr p-p- X c+c- Grgr p+p- if the three loci are not linked?

c+ __ Needed for purple color expression in flowers and petioles (dominantly epistatic to the p locus)
c-c- Produces white flowers and green petioles

Gr__ Dark green leaves . . . grgr Light green leaves
p+ __ Purple petioles . . . p-p- Green petioles

Note that since c-c- and p-p- both produce green petioles and we have a gene-gene interaction where only plants with the genotype c+ __ p+ __ have purple petioles.

Cross c+c- grgr p-p- X c+c- Grgr p+p-

Phenotype ... Genotype ... number
Colored flowers, dark leaves, purple petioles ... c+__ Gr__ p+__... 3/4 X 1/2 X 1/2 = 3/16 = 3
Colored flowers, dark leaves, green petioles ... c+__ Gr__ p-p- ... 3/4 X 1/2 X 1/2 = 3/16 = 3
Colored flowers, light leaves, purple petioles ... c+__ grgr p+__ ... 3/4 X 1/2 X 1/2 = 3/16 = 3
Colored flowers, light leaves, green petioles ... c+__ grgr p-p- ... 3/4 X 1/2 X 1/2 = 3/16 = 3
White flowers, dark leaves, green petioles ... c-c- Gr__ p+__ . AND . c-c- Gr__ p-p- ... 1/4 X 1/2 X 1 = 1/8 or 2/16 = 2
White flowers, light leaves, green petioles ... c-c- gr__ p+__ . AND . c-c- gr__ p-p- ... 1/4 X 1/2 X 1 = 1/8 or 2/16 = 2

3 colored flowers, dark leaves, purple petioles: 3 colored flowers, dark leaves, green petioles: 3 colored flowers, light leaves, purple petioles: 3 colored flowers, light leaves, green petioles: 2 white flowers, dark leaves, green petioles: 2 white flowers, light leaves, green petioles:

Genetics Problems (Mode of Inheritance)
1) Two epistatic loci are not linked. The stubby clear wing allele is dominantly epistatic to the large wing locus. At the large wing locus, the large brown allele is dominant to the large tan allele.

P cross: ++ bb X -- BB
F1 cross: +- Bb X +- Bb

Phenotype (genotype) . . . . . . . . . . . . . .Observed . . . . . . . . . Expected
Stubby clear wings (+_ _ _ ) . . . . . . . . . . . .230 . . . . . . . . . . . . 325 X 12/16 = 243.75
Large brown wings (- - B _ ) . . . . . . . . . . . . . 70 . . . . . . . . . . . . 325 X 3/16 = 60.94
Large tan wings (- - bb ) . . . . . . . . . . . . . . . . 25 . . . . . . . . . . . . 325 X 1/16 = 20.31

2) Two epistatic loci are not linked. The red leaf allele is recessively epistatic to the green/fleck locus. At the green/fleck locus, the allele for flecks is dominant to the unflected allele.

P cross: FF gg X ff GG
F1 cross: Ff Gg X Ff Gg

Phenotype (genotype) . . . . . . . . . . . . . .Observed . . . . . . . . . Expected
Red leaves (_ _ gg ) . . . . . . . . . . . . . . . . . . . . .63 . . . . . . . . . . . . 230 X 4/16 = 57.5
Green leaves (f f G _ ) . . . . . . . . . . . . . . . . . . . 44 . . . . . . . . . . . . 230 X 3/16 = 43.125
Green leaves with white flecks (F_ G_ ) . . . . 123 . . . . . . . . . . . . 230 X 9/16 = 129.375

3) Two epistatic loci are not linked. The short black feather allele is dominantly epistatic to the long feather locus. At the long feather locus, the long tan feather allele is dominant to the long brown allele.

P cross: SS TT X ss tt
F1 cross: Ss Tt X Ss Tt

Phenotype (genotype) . . . . . . . . . . . . . .Observed . . . . . . . . . Expected
Short black feathers (S _ _ _ ) . . . . . . . . . . . 118 . . . . . . . . . . . . 163 X 12/16 = 122.25
Long brown feathers (ss tt ) . . . . . . . . . . . . . . 12 . . . . . . . . . . . . 163 X 1/16 = 10.19
Green leaves with white flecks (F_ G_ ) . . . . .33 . . . . . . . . . . . . 163 X 3/16 = 30.56