Study behavioral objectives 8, 9, 10, 11. Read the pages indicated by ODU Biology 108N: Readings - Delta D-3. Work the following problems involving  monohybrid crosses. There are two types of problems presented on this web page. The first type is where you are given the genotypes of the parents and using the Punnett square you determine the genotypes and phenotypes of the offspring (see behavioral objective 8 and 9). The second type is where you are given information concerning the offspring (phenotypes and ratios) and you are asked to determine the genotypes of the parents (see behavioral objective 10).  You can not use the Punnett square to solve this type of problems. An explanation for solving this type of problem will be explained below. 

9. In the following questions, assume  tall (TT or Tt) is  dominant over dwarf (tt) in garden pea plants. For each of the crosses below, give the probable offspring by answering questions "a, b, and c ". 

                   a) Chances of getting tall individuals. 
                   b) Chances of getting dwarf individuals. 
                   c) Chances of getting heterozygous individuals. 

 Two  tall parents one homozygous and one heterozygous. 
a.___________________ 
b.___________________ 
c.___________________ 
 

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10. In the following question, assume  tall (TT or Tt) is  dominant over dwarf (tt) in garden pea plants. For each of the crosses below, give the probable offspring by answering questions "a, b, and c ". 

                   a) Chances of getting tall individuals. 
                   b) Chances of getting dwarf individuals. 
                   c) Chances of getting heterozygous individuals. 

Two heterozygous tall parents. 
a.___________________ 
b.___________________ 
c.___________________ 
 
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11. In the following question, assume  tall (TT or Tt) is  dominant over dwarf (tt) in garden pea plants. For each of the crosses below, give the probable offspring by answering questions "a, b, and c ". 

                   a) Chances of getting tall individuals. 
                   b) Chances of getting dwarf individuals. 
                   c) Chances of getting heterozygous individuals. 

One tall heterozygous  and one dwarf homozygous parent. 
a.___________________ 
b.___________________ 
c.___________________ 

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12. In the following questions, assume  tall (TT or Tt) is  dominant over dwarf (tt) in garden pea plants. For each of the crosses below, give the probable offspring by answering questions "a, b, and c ". 
 
                   a) Chances of getting tall individuals. 
                   b) Chances of getting dwarf individuals. 
                   c) Chances of getting heterozygous individuals. 

Two dwarf parents. 
a.___________________ 
b.___________________ 
c.___________________ 

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13. In the following question, assume  color black  (BB or Bb) is  dominant over brown (bb) in guinea pigs. Write the possible F1 (a, b, c, d ) for each of the following crosses. 

                   a) Chances of getting black individuals. 
                   b) Chances of getting brown individuals. 
                   c) Chances of getting black heterozygous individuals. 
                   d) Phenotypic ratio. 

Two heterozygous black parents. 
a.___________________ 
b.___________________ 
c.___________________ 
d.___________________ 
 

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14. In the following question, assume  color black  (BB or Bb) is  dominant over brown (bb) in guinea pigs. Write the possible F1 (a, b, c, d ) for each of the following crosses. 

                   a) Chances of getting black individuals. 
                   b) Chances of getting brown individuals. 
                   c) Chances of getting black heterozygous individuals. 
                   d) Phenotypic ratio. 

One  heterozygous black and one homozygous brown  parent. 
a.___________________ 
b.___________________ 
c.___________________ 
d.___________________ 
 

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15. In the following question, assume  color black  (BB or Bb) is  dominant over brown (bb) in guinea pigs. Write the possible F1 (a, b, c, d ) for each of the following crosses. 

                   a) Chances of getting black individuals. 
                   b) Chances of getting brown individuals. 
                   c) Chances of getting black heterozygous individuals. 
                   d) Phenotypic ratio. 

One  homozygous black parent   and one homozygous brown parent. 
a.___________________ 
b.___________________ 
c.___________________ 
d.___________________ 
 
 
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16. In the following question, assume  in guinea pigs  that short hair (SS or Ss ) is dominant over long hair (ss). Write the probable F1 (a, b, c, d, and e) for each of the following. 

                   a) Chances of getting short-haired  individuals. 
                   b) Chances of getting long-haired  individuals. 
                   c) Chances of getting heterozygous individuals. 
                   d) Phenotypic ratio if possible. 
                   e) Genotypic ratio if  possible 

Two homozygous long-haired parents. 
a.___________________ 
b.___________________ 
c.___________________ 
d.___________________ 
e.___________________ 

Click here to check answer.   click 
 
 
 

17. In the following question, assume  in guinea pigs  that short hair (SS or Ss ) is dominant over long hair (ss). Write the probable F1 (a, b, c, d, and e) for each of the following. 
 
                   a) Chances of getting short-haired  individuals. 
                   b) Chances of getting long-haired  individuals. 
                   c) Chances of getting heterozygous individuals. 
                   d) Phenotypic ratio if possible. 
                   e) Genotypic ratio if  possible 

Both  heterozygous short-haired  parents. 
a.___________________ 
b.___________________ 
c.___________________ 
d.___________________ 
e.___________________ 
 
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18. In the following question, assume  in guinea pigs  that short hair (SS or Ss ) is dominant over long hair (ss). Write the probable F1 (a, b, c, d, and e) for each of the following. 
 
                   a) Chances of getting short-haired  individuals. 
                   b) Chances of getting long-haired  individuals. 
                   c) Chances of getting heterozygous individuals. 
                   d) Phenotypic ratio if possible. 
                   e) Genotypic ratio if  possible 

    One homozygous long-haired and one homozygous short-haired individual.. 
a.___________________ 
b.___________________ 
c.___________________ 
d.___________________ 
e.___________________ 
 
Click here to check answer.   click 
 
 
 

19. In the following question, assume  in guinea pigs  that short hair (SS or Ss ) is dominant over long hair (ss). Write the probable F1 (a, b, c, d, and e) for each of the following. 

                   a) Chances of getting short-haired  individuals. 
                   b) Chances of getting long-haired  individuals. 
                   c) Chances of getting heterozygous individuals. 
                   d) Phenotypic ratio if possible. 
                   e) Genotypic ratio if  possible 

    One heterozygous short-haired and one homozygous long-haired parent. 
a.___________________ 
b.___________________ 
c.___________________ 
d.___________________ 
e.___________________ 

Click here to check answer.   click 
 
 
 

As mentioned above there are two types of problems which may be asked to solve. The problems above involve giving the parents and determining the offspring. These problems  can be determined by using the Punnett square. 

The second type of problems are where information  concerning the offspring is given and you are asked to determine the genotypes of the parents. You can not use the Punnett square method to solve these problems. 

Example: In the following problems, assume that in some insects long-winged (LL or Ll) is dominant over short-winged (ll). 

If 50% heterozygous long-winged and 50% short-winged insects were found in one generation of offspring, find the possible genotypes of both parents. Note - Information concerning the F1 offspring is given and you are asked to determine the genotypes of the parents. 

The method used here is as follows: 

Draw two lines and label as P1 and P2. Each line represents a single set of genes for the parents. 

     P1        _________________         X      P2 ___________________ 
 

List genotype of the F1 offspring as much as possible. 

If 50% heterozygous long-winged and 50% short-winged insects were found in one generation of offspring, find the possible genotypes of both parents. 

 Offspring:                        Ll (50%  long-winged) 
                                        ll   (50% short-winged) 

At this point you do not need to be concerned with the frequency (50%) 

Important: Each individual offspring always receive only one allele from each parent. 

The offspring with the genotype  "Ll"  above must have received the "L"  from one parent and the " l "from the other parent. 

Therefore the parents  are  P1     L               x          P2    l 
                                                ______                      _______ 

The offspring with the genotype  "ll" above must have received the  "l"  from each parent. 

Therefore the parents are   P1      Ll              x          P2    ll 
                                                 _____                        _____ 

Now you can check your answer using the Punnett square and see if the frequency is 50% Ll  and 50% ll. 
 
 

Use this method in solving the following problems. 
 

20. In the following problem, assume that in some insects long-winged (LL or Ll) is dominant over short-winged (ll). 

If 50% heterozygous long-winged, 25% homozygous long-winged and 25% short-winged insects were found in one generation of offspring, fine the possible genotypes of both parents. 
 
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21. In the following problem, assume that in some insects long-winged (LL or Ll) is dominant over short-winged (ll). 

If 50% of the generation were short-winged, what would be the genotypes of both parents? 
 
 
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22. In the following problem, assume that smooth-seed coat  (SS or Ss) is dominant over wrinkled coated seeds (ss). 

If a phenotypic ratio of 1:1 resulted when these two plants were crossed, give the possible genotypes of both parents. 
 
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23. In the following problems, assume that smooth-seed coat  (SS or Ss) is dominant over wrinkled coated seeds (ss). 

What percent of the offspring would be wrinkled-coated seeds if both parents were heterozygous? 
 
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24. In the following problems, assume that smooth-seed coat  (SS or Ss) is dominant over wrinkled coated seeds (ss). 

Give the phenotypes of both parents if a 3:1 ratio resulted in the offspring. 
 
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25. Use (TT or Tt) for tall and (tt) for dwarf. In a homozygous tall garden pea plant is crossed with one homozygous dwarf plant, give the phenotypes of the (Punnett square): 

F1 offspring - 
 

F2 offspring - 

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26. Progeny of the F1 when crossed back with its tall parent - 

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27.Progeny of the F1 when crossed back with its dwarf parent - 
 
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This is the end of lesson two. In the next lesson you will learn to how to work genetic problems involving  two sets of genes at the same time. These problems will also involve the use of the Punnett square.  Click here to go back to the home pages and lesson three Dihybrid Problems.   click 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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