Problems

 

1) As Mendel discovered, gray seed color in peas is dominant to white.  In the  

            following experiments, parents with known phenotypes but unknown genotypes

            produced the listed progeny:

                                                                Progeny

 

Parents                                         Gray                White

 

  (a) gray x white                                   82               78

  (b) gray x gray                                  118               39

  (c) white x white                                   0               50

  (d) gray x white                                  74                 0

  (e) gray x gray                                    90                 0

 

Using the letter G for the gray gene and g for white, give the most probable genotype of each parent.

 

2)      Groff and Odland found a variety of cucumber whose flowers failed to open when mature. These flowers failed to open when mature.  These flowers could nevertheless be pollinated by opening them artificially.  The results of their experiments were:

3)       

                                                   Phenotypes of Offspring

Parents                             Open Flowers        Closed Flowers

 

closed x open                          all                                  none

F1 (of above) x F1                    145                                 59

closed x F1                                81                                 77     

 

Define symbols for the genes involved and indicate the genotypes of:  (a) The closed parents.  (b) The open parents.  (c) The F1.

 

4)      In dogs dark coat color is dominant over albino, and short hair is dominant over long  

      hair.  If these effects are caused by two independently segregating gene pairs, write the

      most probable genotypes for the parents of each of the following crosses, using the

      symbols C and c for the dark and albino coat-color alleles, and S and s for the short-and

      long-hair alleles, respectively.

 

 

 

 

 

 

 

 

     

Phenotypes of Offspring

                                                                         

                                                Dark    Dark  Albino    Albino

Parental Phenotypes             Short     Long  Short      Long

(a) dark short x dark short        89         31        29         11

(b) dark short x dark long         18         19          0           0

(c) dark short x albino short      20           0        21           0

(d) albino short x albino short      0            0        28          9

(e) dark long x dark long              0          32         0         10

(f) dark short x dark short          46          16          0           0

(g) dark short x dark long           29          31         9          11

 

5)      In Drosophila melanogaster one gene pair is known to affect wing size, and the allele for normal long wings (vg+) in this gene pair has a dominant effect over the allele for short vestigial wings (vg).  Another independently assorting gene pair affects body color:  The allele for normal grey body color (e+) is dominant to that for ebony body color (e).  A cross is made between a fly with normal wings and ebony body color and a fly with vestigial wings and normal body color.  The normal-appearing F1 are crossed among each other and 512 F2 flies are raised.  What phenotypes would you expect in the F2 and in what numbers would you expect to find them?

 

6)      In corn a pair of genes determines leaf shape and another pair determines pollen shape.  A ragged-leafed plant with round-pollen was crossed to a ragged-leafed plant with angular-pollen , and the resultant progeny were classified as follows:

 

Class 1:  186 ragged-leaf round-pollen

Class 2:  174 ragged-leaf angular-pollen

Class 3:    57 smooth-leaf round-pollen

Class 4:    63 smooth-leaf angular-pollen

   Total    480

 

(a)    Using alphabetical letters of your choice, designate the genes for the different leaf and pollen characters.  (b) On the basis of the symbols given in (a), provide genotypes for the two parents.  (c) According to your hypothesis what numbers would you have expected for each of the four classes of progeny?  (d) Test your hypothesis statistically using the chi-square method (Chapter 8) and indicate whether you accept or reject your hypothesis.

 

7)      In foxes a platinum mutation arose in Norway in 1933 that appeared to be a dominant allele

      of the silver gene.  The platinum mutant was then mated to silver animals to obtain an F1.

      About 50 matings were than made between F1 platinum and F1 platinum which produced an

      F2 of about 100 platinum foxes and 50 silver.  How can this ration be explained?

 

8)      Among the various coat colors in mice, there may be yellow, agouti, or black.  Crosses made between certain mice provided the following results:

    Parents                                         F1 offspring

cross 1             yellow x yellow             2/3 yellow: 1/3 agouti

cross 2             yellow x agouti              1/2 yellow: 1/2 agouti

cross 3             yellow x black                          1/2 yellow: 1/2 black

cross 4             black x agouti                           all agouti

 

What phenotypic ratios would you expect from the following crosses: (a) F1 yellow (cross 1) x F1 yellow (cross 2)?  (b) F1 agouti (cross 4) x F1 yellow (cross 2)?  (c) F1 agouti (cross 4) x F1 yellow (cross 3)?

 

9)      Abnormal eye shape in Drosophila may be caused by a variety of mutant genes, dominant or

      recessive, sex-linked or autosomal.  One normal-eyed Drosophila melanogaster male from a

      true-breeding normal stock was crossed to two different abnormal-eyed females with the

     following results:

      Progeny of                  Progeny of

                                          female 1                      female 2                     

                                          ♀         ♂                    ♀         ♂

    normal-eyed                 108           0                   51        49

    abnormal-eyed                 0       102                   53        50       

 

10)  In corn the seeds can be colored or white, nonshrunken or shrunken.  Each of these

      characteristics is determined by a separate pair of genes, C and c and Sh and sh.  Hutchison

      crossed a homozygous colored shrunken strain (CC shsh) to a homozygous white non-

      shrunken strain (ccShSh) and obtained a heterozygous colored nonshrunken F1.  The F1 was

      backcrossed to a homozygous recessive white shrunken stock and the progeny were as

      follows:                                                 No. plants

 

                              colored shrunken                        21,379          

                              white nonshrunken                      21,096

                              colored nonshrunken                        638

                               white shrunken                    672          

      What is the recombination frequency between these two genes?

 

11)  Can you distinguish between two gene loci located on the same chromosome that have 50 percent crossing over between them and two gene loci each located on different nonhomologous chromosomes?  Explan.

 

12)  In the tomato the mutant genes o (oblate = flattened fruit), p (peach = hairy fruit), and s (com-pound inflorescence = many flowers in a cluster) were found to be in chromosome 2.  From the following data (testcross mating of an F1 heterozygote for all three genes x homozygous recessive for all three genes) determine:  (a) The sequence of these three genes in chromosome 2.  (b) The genotypes of the homozygous parents used in making the F1 heterozygote.  (c) The recombination distances between the genes.  (d) The coefficient of coincidence.

                                                                   Phenotypes of

                                                            testcross progeny              Number          

                                                                  + + +                                73

                                                                  + + s                                348

                                                                  + p +                                    2

                                                                  + p s                                  96

                                                                  o + +                                110

                                                                  o + s                                    2

                                                                  o p +                                306

                                                                  o p s                                   63 

 

13)  In corn three gene pairs linked on the same chromosome are those for plant color, in which yellow (y) is recessive to green (Y); endosperm shape, in which shrunken (sh) is recessive to full (Sh); and seed color, in which colorless (c) is recessive to colored (C).  Three different plants, I, II, and III, each heterozygous for these three gene loci, although not necessarily heterozygous in the same fashion as the others (i.e., y sh c/Y Sh C, Y Sh c/y sh C, etc.), were backcrossed to homozygous triple recessives, y sh c / y sh c, and produced progeny which had the following phenotypic frequencies:

 

                                                            Numbers Produced by

Heterozygous Plants

Phenotype of                                                       __________________________              

offspring                     I                       II                      III                                                                                             

y sh c                          95                     368                    22

Y Sh C                         100                  387                    23

y Sh C                          3                        21                  390     

Y sh c                           2                       24                  365

y sh C                          20                     4                      96

Y Sh c                          25                     1                      99

y Sh c                           375                    98                    0
Y sh C                          380                    97                     5 
                                    ________        ________     _______            

                                   

                                      1,000            1,000            1,000

           

(a) Using the progeny from any one of the heterozygous plants, propose the gene order and the recombination distances between the three genes.  (b) On the basis of  (a)——, compute the coefficient of coincidence.  (c) For the plant analyzed in (a) and (b), describe the frequency changes you would expect among its progeny if interference were increased.  (d) Give the exact genotypes for each of the two homologous chromosomes bearing the three genes in heterozygous plants, I, II, and III.