Biology 115                                                                              Name___________________

Exam I                                                                                     Discussion Section________

Spring, 2003

 

Circle the most correct answer:  (80 pts)

 

  1. In watermelons, bitter fruit (B) is dominant over sweet fruit (b), and yellow spots (S) are dominant over no spots(s).  The genes for these two characteristics assort independently.  A homozygous plant that has bitter fruit and yellow spots is crossed to a homozygous plant that has sweet fruit and no spots.  If an F1 progeny plant from this cross is backcrossed to the sweet, nonspotted parent, what phenotypic ratio is expected in the offspring?

 

a.       3:1                         d.  1:1

b.      1:1:1:1                    e.  2:1:1

c.       9:3:3:1

 

  1. A woman has blood type A and is also type M.  She has a child with blood type AB MN.  Which of the following men might be the father of this child?

 

a.  George        O    MN

            b.  Henry          AB  M

            c.  Claude         A     N

            d.  Bill              B     MN

            e.  Tom            O     N

 

  1. The type of inheritance shown in the pedigree below is most likely:  (This is a real pedigree of a family in Sao Paulo, Brazil, where a condition called ectodactyly was segregating.)

 

 

 

 

 

 

 

 

 

 

 

    1. autosomal dominant
    2. autosomal recessive
    3. sex-linked (X-linked) recessive
    4. sex-linked (X-linked) dominant
    5. Y-linked

 

  1. A panel of cell lines was created from mouse-human somatic cell fusions.  Each hybrid line was examined for the presence of human chromosomes and for the production of enzyme X.

 

 

 

 

 

 

 

 

 

 

 

            On the basis of these results, which chromosome has the gene that codes for

            enzyme X?

 

a.       2

b.      4

c.       6

d.      8

e.       none of the above is correct

 

  1. Huntington disease (HD) is a rare autosomal dominant condition in humans that is usually not expressed until an individual reaches middle age.  HD is a neurological disorder that ultimately is lethal and practically all affected individuals are heterozygous for the condition.  A woman, who eventually expresses the symptoms of HD, has a son.  He marries, has a daughter, and is killed in an auto accident at the age of 26.  His daughter eventually marries and has a son.  What is the probability that this son carries the HD allele?  (Assume all those who marry into this family are normal.)

 

    1. 1/2
    2. 0
    3. 1/4
    4. 1/8
    5. 1/16

 

 

 

 

 

 

 

 

 

 

  1. In summer squash, a cross of a white fruit, disk-shaped fruit plant with a yellow fruit, disk-shaped fruit plant resulted in offspring of 3/8 white, disk-shaped fruit plants, 3/8 yellow, disk-shaped fruit plants, 1/8 yellow, sphere-shaped fruit plants, and 1/8 white, sphere-shaped fruit plants.  The dominant alleles for white fruit and disk-shaped fruit can be represented by W and D, respectively while the recessive alleles for yellow fruit and sphere-shaped fruit can be represented by w and d, respectively.  What are the genotypes of the parents in this cross?

 

    1. Ww dd x Ww Dd
    2. Ww Dd x ww Dd
    3. Ww Dd x ww dd
    4. WW Dd x ww Dd
    5. Ww DD x ww Dd

 

  1. In humans, red-green colorblindness is caused by a sex-linked recessive allele.  A woman has normal vision but her father is colorblind.  She marries a man with normal vision but whose own father was colorblind.  What is the probability that their first child will be colorblind?

 

    1. 0
    2. 1/8
    3. 1/4
    4. 1/2
    5. 1/16

 

  1. In Drosophila, a recessive autosomal allele, ebony (e), produces a black body color when homozygous and at an independently assorting autosomal locus, the recessive allele, black (b), also produces a black body color when homozygous.  Flies that are ee b+_, e+_ bb, or ee bb are phenotypically identical and have black bodies.  Flies of e+_b+_ genotype have the wild-type grey body color.  Ebony flies of eeb+b+ genotype are crossed to black e+e+bb flies.  The F1 flies are then allowed to intercross with each other to produce an F2.  What will be the expected phenotypic ratio in the F2?

 

    1. 13:3
    2. 9:3:3:1
    3. 9:4:3
    4. 12:3:1
    5. 9:7

 

 

 

 

 

 

  1. Two genes, a and b, are located 6 map units apart on the genetic map of Drosophila.  If one is able to look at 100 meiotic events in Drosophila, in how many of these 100 meiotic events should one expect to find a crossover event (chiasma) occurring between a and b?

 

    1. 6
    2. 3
    3. 12
    4. 0
    5. at least 50

 

  1. The trait in the pedigree is for a relatively common genetic condition.  Based upon the most likely mode of inheritance of this trait, what is the probability that a child of the first cousin marriage (III-2 and III-3) will have this trait?

 

 

 

 

 

 

 

 

 

    1. 1/4
    2. 1/2
    3. 1/9
    4. 1/12
    5. 1/6

 

 

  1. A plant of AB/ab genotype is testcrossed by crossing it to an ab/ab plant.  If the two loci are 10 map units apart, what percentage of the progeny are expected to be AB/ab?

 

    1. 10%
    2. 20%
    3. 45%
    4. 5%
    5. 90%

 

 

 

 

 

 

 

 

 

 

  1. You have been given a virgin Drosophila female that has bristles on her thorax that are much shorter than the normal wild-type.  She is mated with a wild-type male (with long bristles) and the following F1 progeny are obtained:  1/3 short-bristled females, 1/3 long-bristled females, and 1/3 long-bristled males.  A cross of the F1 long-bristled females with their brothers gave only long-bristled F2 flies of both sexes.  A cross of F1 short-bristled females with their brothers gave 1/3 short-bristled females, 1/3 long-bristled females, and 1/3 long-bristled males.  The best hypothesis to account for these results is:

 

    1. A mutant sex-linked allele is present that causes short bristles when heterozygous with the wild-type allele but is lethal when hemizygous or homozygous.
    2. Two different gene pairs that affect bristle length are segregating, one is autosomal and the other is sex-linked.
    3. Two autosomals gene pairs are segregating that affect bristle length.  One gene locus has a dominant allele that suppresses the activity of the normal allele at the second locus.
    4. One autosomal gene locus is involved.  It contains an allele that causes short bristles in females when heterozygous and short bristles in males when homozygous.
    5. Short bristles are caused by a mutant allele carried on the Y chromosome.

 

 

  1. An organism is diploid with a XXY sex chromosome complement.  It could be a:
    1. male fruit fly or male human
    2. male fruit fly or female human
    3. female fruit fly or male human
    4. female fruit fly or female human
    5. intersex fruit fly or male human

 

  1. In humans the diploid number of chromosomes is 46.  How many chromosomes (as opposed to chromatids) are there in metaphase II of meiosis in humans?

 

    1. 2
    2. 4
    3. 46
    4. 92
    5. 23

 

 

 

 

 

  1. Genes A, B, and C are independently assorting and control production of a black pigment through the production of intermediate molecules in a certain snail species.  Assume that A, B, and C act in a pathway as follows:

   A                  B                  C

colorless à colorless àcolorless à black pigment

 

            The alternative alleles that give abnormal functioning of these genes are designated a, b, and c, respectively.  A black AABBCC male is crossed to a colorless aabbcc female to give a black F1.  The F1 are crossed with each other.  If colorless and black are the only phenotypes observed, what proportion of the F2 are colorless?

 

a.       1/64

b.      37/64

c.       9/64

d.      27/64

e.       3/16

 

  1. In Drosophila the recessive alleles for brown (bw) and scarlet eyes (st) represent two independently assorting autosomal genes.  These genes interact so that the bwbw stst genotype gives a white eye color.  If a bwbw st+st+ fly is crossed to a bw+bw+ stst fly, what proportion of the F2 will have white eyes?

 

    1. 13/16
    2. 7/16
    3. 1/4
    4. 1/16
    5. 3/4

 

  1. Indicate whether each of the following statements is true (T) or false (F).  (10 pts.)

 

_____ a.  Homologous chromosomes separate from each other during meiosis I.

 

_____ b.  A two-strand double crossover between two genes will lead to two recombinant chromatids.

 

_____ c.  One would use two degress of freedom when testing the acceptability of data fitting a 13:3 ratio using the chi-square test.

 

_____d.  The genetic distance between two genes located far apart on a chromosome will be more accurate than the genetic distance between two genes located close together on the same chromosome because double crossovers do not occur between genes that are close to each other.

 

_____ e.  Segregation of the two alleles in a heterozygous individual usually occurs during anaphase II of meiosis?  (Assume there is no crossing over between the gene and the centromere.)

  1. You are told that in a family with two children, one of them is a girl. What is the probability that the other is also a girl? (This is actually a difficult question and the correct answer is not the obvious answer. Do this one last.) (2 pts)

 

 

 

  1. In Drosophila, cherub wings (ch), black body (b), and cinnabar eyes (cn) result from recessive alleles that are all located on the same autosomal chromosome. A homozygous wild-type fly is crossed with a cherub, black, and cinnabar fly, and the resulting F1 females testcrossed with cherub, black, and cinnabar males. The following progeny were produced from this testcross:

 

                          ch    b+  cn                             105

                          ch+  b+  cn+                            750

                          ch+  b   cn                                40

                          ch+  b+  cn                                  4

                          ch    b   cn                              753

                          ch    b+  cn+                              41

                          ch+  b    cn+                            102

                          ch    b    cn+                                5

                                                                       _________

                               Total                                 1800

 

a.       Determine the linear order of the genes on the chromosome (which gene is

in the middle).   (2 pts)

b.      Calculate the map distances between the three loci. (4 pts)

c.       Determine the coefficient of coincidence and the interference for the three loci. (2 pts)