Study Questions Chapter 13
1. Define incomplete dominance.
2. Give examples of incomplete dominance
3. Explain incomplete dominance in white spotted cats.
4. Explain incomplete dominance in palomino horses.
5. Define codominance
6. What are antigens?
7. Explain in detail the ABO blood groups
8. Explain the H antigen.
9. What type of genetic relationship is H related to the ABO inheritance?
10. What is the Bombay phenotype?
11. What is the most frequent blood type in the United States?
12. What is the Rh factor? What type of inheritance do Rh genes follow?
13. How do you produce novel phenotypes?
14. Give examples of how novel phenotypes modify mendelian traits.
15. Define epistasis
16. What is dominant epistasis. Example
17. What is recessive epistasis. Example
18. What is the molecular explanation beyond dominant and recessive epistasis?
19. Explain the epistatic relationship in the color of the fur in Labrador retrievers.
20. What is gene duplication. Example
21. What are essential genes?
22. How are mendelian ratios modified if a dominant gene is lethal?
23. How are mendelian ratios modifid if a recessive gene is lethal?
24. What are suppressor genes? Example
25. How is gene expression influenced?
26. Name and explain the factors that influence gene expression?
27. How can the environment influence the expression of genes? Examples.
28. What is penetrance, examples.
29. What is expressivity, examples.
Problems
Dominant epistasis
1. In the summer squash (Cucurbita pepo) white fruit is controlled by a dominant allele,
W, and colored fruit by its recessive, w. In ww plants the color alleles (Y for yellow
fruit, are dominant to y for green fruit. are expressed.
a. What is the phenotype of the F1 of a white plant of genotype WWyy crossed with a
homozygous yellow plant?
b. What ratio is expected in the F2? What type of interaction is involved?
c. A cross between a plant with yellow fruit and a plant with white fruit produced 58
white: 39 yellow: 16 green. What are the genotypes of the parents?
2. In a certain breed of dog, the alleles B and b determine black and brown coats
respectively. However, the allele Q of a gene on a separate chromosome is epistatic to
the B and b color alleles resulting in a gray coat (q has no effect on color. . If animals of
genotype B/b ; Q/q are intercrossed, what phenotypic ratio is expected in the progeny?
A.
B.
C.
D.
E.
9 gray, 3 brown, 4 black
1 black, 2 gray, 1 brown
9 black, 6 brown, 1 gray
9 black, 4 gray, 3 brown
12 gray, 3 black, 1 brown
3. In mice the allele for color expression is C (c = albino). Another gene determines
color (B = black and b = brown). Two mice that are Cc Bb are mated. What proportion of
progeny will be brown (assume complete dominance at each locus. ?
A.
9/16
B.
1/16
C.
9/64
D.
3/16
E.
3/16
4. The production of the purple pigment anthocyanin in flowers is accomplished via a
biosynthetic pathway. A biosynthetic pathway consists of a series of enzymatically
catalyzed reactions resulting in the creation of a final product via several intermediates.
A mutation in either one of the enzymes will result in the inability to produce
anthocyanin and thus cause the flowers to be white. Suppose that Enzyme 1 is encoded
by the “A” gene (A = functional enzyme 1; a = nonfunctional enzyme 1. and Enzyme 2
is encoded by the “B” gene (B = functional enzyme 2; b = nonfunctional enzyme 2. .
(i)
What chemical is accumulated in a plant that has the genotype “aa”? What will
be the color of the flowers?
(ii)
What chemical is accumulated in a plant that has the genotype “bb”? What will
be the color of the flowers?
(iii)
If an AAbb plant was crossed with a plant that is aaBB, what would be the
genotype of the progeny? What will be the color of the flowers?
5. In a certain breed of mink, the alleles B and b determine black and brown coats
respectively. However, the allele G of a gene on a separate chromosome is epistatic to
the B and b color alleles resulting in a gray coat (g has no effect on color). If animals of
genotype Gg Bb are intercrossed, what phenotypic ratio is expected in the progeny?
A.
B.
C.
D.
E.
1 black, 2 gray, 1 brown
9 gray, 3 brown, 4 black
9 black, 4 gray, 3 brown
12 gray, 3 black, 1 brown
9 black, 6 brown, 1 gray
Recessive epistasis
6. Feather color in budgies is determined by two different genes that affect the
pigmentation of the outer feather and its core. Y_B_ is green; yyB_ is blue; Y_bb is
yellow; and yybb is white.
A green budgie is crossed with a blue budgie. Which of the following results is not
possible?
A. all white offspring
B. all blue offspring
C. all yellow offspring
D. all green offspring
E. All of the above are possible, but with different probabilities.
7 Two blue budgies were crossed. Over the years, they produced 22 offspring, 5 of
which were white. What are the most likely genotypes for the two blue budgies?
A.
B.
C.
D.
E.
yyBB and yybb
yyBb and yyBb
yyBb and yybb
yyBB and yyBB
yyBB and yyBb
8. The inheritance of color in budgies is an example of what genetic phenomenon?
A. penetrance B. polygenic inheritance C. epistasis D. dominance E. pleiotropy
9. In sweet peas the allele C is needed for color expression (c results in no colorwhite. .
The precise color expressed is determined by the alleles R (red). and r (blue). A cross
between certain red and blue plants resulted in progeny as follows:
3/8 red
3/8 blue
1/4 white
Supressor genes
10.
In Drosophila the eye color peach is determined by an autosomal recessive
allele p. On another chromosome the autosomal recessive s suppresses peach,
restoring the wild-type red eye color. When two pure-breeding red strains 1 and 2
are intercrossed, the F1 is also red. However when the F1 is backcrossed to strain 1,
the progeny show 3/4 red and 1/4 peach flies. The genotype of the strain 1 must have
been
A.
p+p+s+s+
B.
p+p
ss
C.
pp
s+s+
D.
p+p
s+s
E.
pp ss
Lethal genes
11. In chickens the dominant allele Cr produces the creeper phenotype (having
extremely short legs. . However the creeper allele is lethal in the homozygous condition.
If two creepers are mated, what proportion of the living progeny will be creepers?
A.
1/4
B.
1/2
C.
3/4
D.
1/3
E.
2/3
12. In Drosophila, a mutant strain has plum-colored eyes. A cross between a plumeyed male and a plum-eyed female gives 2⁄3 plum-eyed and 1⁄3 red-eyed (wild-type.
progeny flies. A second mutant strain of Drosophila, called stubble, has short
bristles instead of the normal long bristles. A cross between a stubble female and a
stubble male gives 2⁄3 stubble and 1⁄3 normal-bristled flies in the offspring.
Assuming that the plum gene assorts indepen-dently from the stubble gene, what
will be the phenotypes and their relative proportions in the progeny of a cross
between two plum-eyed, stubble-bristled flies? (Both genes are autosomal)
Incomplete Dominance
13. In cattle, roan coat color (light red) occurs in the heterozygous (Rr) offspring
of red (RR) and white (rr) homozygotes. When two roan cattle are crossed, the
phenotypes of the progeny are found to be in the ratio of 1 red:2 roan:1 white.
a. What type of inheritance is this?
b. Which of the following crosses could produce the highest percentage of roan cattle?
A. white x roan
B. roan x roan
C. red x roan
D. red x white
E. All of the above crosses would give the same percentage of roan.
14. Roan color (Rr) in the above cattle is the result of red and white color genes.
How would one produce a herd of pure-breeding roan-colored cattle?
A.
B.
C.
D.
E.
cross roan with white
cross red with white
cross roan with roan
cross roan with red
It cannot be done.
Answers
1.
a. All WwYy, all white.
b. 12 white, 3 yellow 1 green. Dominant epistasis.
c. wwYy x WwYy
2.E
3.B
4. Answers:
i. Initial compound will accumulate. The flowers will be white.
ii. Intermediate A will accumulate. The flowers will be white.
iii. The progeny will be AaBb and will have purple flowers.
5. D
6. E
7. B
8. C
9. D
10.E
11. E
12.
Answer: For either of the stubble or plum mutants, a cross of two mutant
individuals gives a 2 mutant:1 wild-type progeny ratio. This 2:1 ratio is a
modified 3:1 ratio from a monohybrid cross, where 25 percent of the progeny—
the homozygous mutant individuals —die. We can denote the cross (using Pp for
plum, Ss for stubble) as Pp Ss x Pp S s. Any PP and/or SS progeny will be
inviable.
13.a. Incomplete dominance
b. D
14. E