8/17/2019 Genetics Problem Set 2

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PCB 3063

Problem Set 2

1. 

Magical ability is a dominant trait controlled by two loci. Consider the following

cross:aaBb x Aabb

a.  What are the phenotypes of these two individuals?b.  Use a Punnett square to determine the genotypic and phenotypic probabilities in

the progeny.

2. In humans, alkaptonuria is a metabolic disorder in which affected persons produce

black urine. Alkaptonuria results from an autosomal allele (a) that is recessive to the

allele for normal metabolism ( A). Sally has normal metabolism, but her brother has

alkaptonuria. Sally’s father has alkaptonuria, and her mother has normal metabolism.a.  Construct a pedigree of this family and indicate the genotypes of Sally, her

mother, her father, and her brother.

b.  If Sally’s parents have another child, what is the probability that this child willhave alkaptonuria?

3. The following pedigree is for an X-linked trait:( Note: the “carrier” symbol was not used in this pedigree.)

a.  Is this trait dominant or recessive?

b. 

Indicate the genotypes of all the individuals in the pedigree.

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4. The following pedigree illustrates the inheritance of Nance-Horan syndrome (n), a rare 

X-linked genetic condition in which affected persons have cataracts andabnormally shaped teeth. ( Note: the “carrier” symbol was not used in this

 pedigree.) 

If III-2 and III-7 mated, what would be the expected genotypic and phenotypic ratiosin their progeny? Draw a Punnett square.

5.  The cross between AaBb and aabb yielded the following phenotypic proportions:

AB 37.4%Ab 11.9%aB 12.6%

ab 38.1%

a.  What do the symbols on the premise represent? b.  What do the symbols on the table represent?

c.  What is the configuration of the alleles in the heterozygous parent?d.  What is the map distance between the two genes?

6. The cross between AaBb and aabb yielded the following results:AB 97

Ab 159ab 105

aB 164

a.  What is the configuration of the alleles in the heterozygous parent? b.  What is the map distance between the two genes?

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7.  The cd-sr  (cardinal eyes-stripe body) linkage cross yielded the following results:cd 

+  sr 

+  7%

cd +  sr   44%cd 

  sr 

+  43%

cd   sr   6%

a.  What do the symbols on the premise represent? b.  What do the symbols on the table represent?

c.  What is the configuration of the alleles in the heterozygous parent?d.  What is the map distance between the two genes?

8.  The genes dumpy wing (dp), clot eye (cl ), and apterous wing  (ap) are linked onchromosome 2 in Drosophila. In a series of two-point mapping crosses, the following

crossing-over frequencies were obtained:dp-ap  44%

dp-cl   4%ap-cl   39%

a.  What do the symbols in the premise represent?

 b.  What do the symbols on the table represent?c.  Construct a linkage map.

9.  In Drosophila, ebony body color  (e), scarlet eyes ( st ), and spineless bristles ( ss) areautosomally linked. When a wild type female (heterozygous for all three genes) was

test-crossed with an ebony, scarlet, spineless male, the following progeny wasobtained:

wild type 43ebony 278

scarlet 5spineless 52

ebony, scarlet 50ebony, spineless 3

scarlet, spineless 283ebony, scarlet, spineless 41

a.  What do the symbols in the premise represent?

 b.  What do the words on the table represent?c.

 

What is the configuration of the alleles in the heterozygous parent?

d.  Construct a linkage map showing map distances.e.  Calculate the coefficient of coincidence and the interference.

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10. Waxy endosperm (wx), shrunken endosperm ( sh) and yellow seedling  ( y) areautosomally linked in corn. A testcross produced the following results:

wild typeyellow

yellow, waxy

yellow, waxy, shrunkenshrunkenyellow, shrunken

waxy, shrunkenwaxy

3030560

6954

30626960174

584188

a.  What is the configuration of the alleles in the heterozygous parent?

 b.  Construct a linkage map showing map distances.c.  Calculate the coefficient of coincidence and the interference.

11. 

In Drosophila, ebony body color  (e), brevis bristles (bv), and rough eyes (ro) areautosomally linked. A test cross yielded the following results:

wild typeebony

 brevisrough

ebony, brevisebony, rough

 brevis, roughebony, brevis, rough

169619

1493

979

621165

a.  What is the configuration of the alleles in the heterozygous parent?

 b. 

Construct a linkage map showing map distances.c.  Calculate the coefficient of coincidence and the interference.

12. In Drosophila, cherub wings (ch), black body, (b) and cinnabar eyes (cn) are

autosomally linked on chromosome 2. A heterozygous fly was mated with a cherub, black and cinnabar fly. The following progeny were produced from the testcross:

cherub, cinnabar 105wild type 750

 black, cinnabar 40cinnabar 4

cherub, black, cinnabar 753cherub 41

 black 105cherub, black 5

a.  What is the configuration of the alleles in the heterozygous parent?

 b.  Construct a linkage map showing map distances.c.  Calculate the coefficient of coincidence and the interference.

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13. The ability to taste the compound PTC is controlled by a dominant allele T , whileindividuals homozygous for the allele t  are unable to taste PTC. In a genetics class of

125 students, 88 can taste PTC and 37 cannot. Calculate the frequency of the T  and t  alleles in this population and the frequency of the genotypes. Assume that the

 population is at Hardy-Weinberg equilibrium.

14. Consider rare disorders in a population caused by autosomal recessive mutations.

From the frequencies of the disorders in the population given, calculate the percentage of carriers (assume that the populations are at Hardy-Weinberg

equilibrium):a.  0.0064

 b.  0.000081c.  1/100