SBI4U                                                                         Mendelian Genetics

 

Name                                                .                  2003 11 25

 

K                                                    20

A                                                      12

Bonus                                 1

 

Instructions:

1. Read over each question carefully. Attempt each question as no marks will be     

    deducted for incorrect responses.

2. Answer all questions on this test booklet. Show your work in pen (neatly).

3. The KICA allotment and mark breakdown is provided at the beginning of each section.

4. Each question is worth one mark unless otherwise specified.

5. Calculators may not be shared. You will forfeit this test if this rule is breached.

6. Do not write in symbols, abbreviations, or shorthand.

 

Initial here that you have read and understood the instructions           .

 

 

1.   In all of Mendel’s monohybrid crosses, the F₂ plants displayed a 3:1 dominant to recessive phenotypic ratio.  Of the plants exhibiting the dominant phenotype, what proportion is homozygous?

A.  one-fourth                          C.        one-third  (2/3 are heterozygote)

B.   one-half                              D.        two-thirds 

2.   Crosses between certain white and red flowered plants result in all pink offspring in the F₁ generation. If two F₁ plants are crossed, what will be the expected phenotypic ratio in the F₂ generation?

            A.  all pink                                C.  1 red : 1 white

             B.  all red                                D.  1 white : 2 pink : 1 red         

3.  In a cross between  AABbCc and aaBbCc, what is the probability that an offspring will have the following genotype:   Aabbcc?    

A.   1/4                                    C.  1/8

B.    1/16 (1 x ¼ x ¼ )                          D.  1/2

4.   In all conditions where a defective gene is on the X chromosome, transmission to the daughter can be           .

          

            A.  only through the mother

            B.  only through the father

            C.  either through the mother or the father (the question does not imply that she’ll be afflicted)

            D.  only by mutation

5.   White colour is dominant over yellow colour in squash. If a heterozygous white-fruited plant is mated to a yellow-fruited plant, one would expect to produce       .

 

A.  all white offspring.

B.   1/2 white ; 1/2 yellow  (Ww x ww)

C.  all yellow offspring

D.  a 3:1 phenotypic ratio of white to yellow

            E.   a 3:1 phenotypic ratio of yellow and white

6.   A child with blood type O has a mother with blood type A and a father with blood type B. The parental genotypes for blood types must be          .

 

A.  I^Ai   and I^Bi                         C.        I^Ai and I^BI^B

B.   I^AI^B and I^Bi                         D.        I^AI^A and I^BI^B

7a. Bomb disposal requires accurate colour vision.  Without knowing the exact genotype, whom would you prefer to dispose of a bomb?     

A.  the son of a man with normal vision and a colour-blind woman.

B.   the daughter of a man with normal vision and a colour-blind woman.

C.  the son of a colour-blind man and a woman who is a carrier.

D.  the daughter of a colour-blind man and a woman who is a carrier.

 

b.   Justify your answer for 7a.

Since a daughter must receive an X from her father, this woman will possess a normal X.

She won’t be colour-blind. In all other cases, there is a possibility of colour-blindness. Would

you take that chance with bomb disposal?

8.   The appearance of the recessive trait in the offspring most probably indicates that             

 

A.  one parent was homozygous dominant and the other parent was hybrid for the trait

B.   neither parent carried a recessive gene for the trait

C.  one parent was homozygous dominant and the other was homozygous recessive for the trait

D.  each parent carried at least one recessive gene for that trait

 

9.   When individuals with straight hair mate with individuals with curly hair, their children have wavy hair. If two individuals with wavy hair mate, what phenotypes and ratios would you predict among their offspring?

 

            A. 3 curly:1 straight       B. 1 curly: 2 wavy: 1 straight     C. 3 wavy: 1 straight     D. 3 wavy: 1 curly

10. When a trait, such as height in humans, is continuously variable over a wide phenotypic range, it is reasonable to suspect that it is exhibiting

A.  epistasis                              C.  pleiotropic effects

B.   multigenic inheritance          D.  none of the above

 

11. If an individual has the genotype Dd, the gametes produced would be

            A.  1/2 Dd and 1/2 Dd                         C.  1/2 D and 1/2 d

            B.  3/4 Dd and 1/4 Dd                          D.  3/4 D and 1/4 d

 

12. Sometimes, one gene pair will interact to control the expression of a second gene     (for example, coat color in Labrador retrievers). This gene interaction is called

           

A.  epistasis                              C.  pleiotropic effects

B.   multigenic inheritance          D.  codominance

 

13. A man who carries an X-linked allele is will pass it on to

      A. all of his daughters  (NONE OF HIS SONS!)

      B. half of his daughters

      C. all of his sons

      D. half of his sons

      E. all of his children

14. White eyes in Drosophila is sex-linked and recessive to red eyes.  This means that

      A. females can never have white eyes

      B. males can never have white eyes

      C. males inherit the white eye trait from both parents

      D. white-eyed females must inherit the trait from each parent

      E. Two of the above are correct.

15. The probability that four coins will come up heads when flipped simultaneously is

      A. ¼ (0.25)            B. ½ (0.5)        C. 1/8 (0.125)             D. 1/16 (0.062)           

16.       How many unique gametes can be produced through independent assortment by an individual with the genotype Aa Bb CC Dd EE?

      A. 4           B. 8      (2x2x1x2x1)     C. 16               D. 32               E. 1/64

17. In cattle, roan colour (mixed red and white hairs) occurs in the heterozygous offspring of red (RR) and white (WW) homozygotes.  Which of the following crosses would produce the highest proportion of roan cattle?

A. red X white  (100% roan in the offspring – the other cases will produce 50% roan)    B. white X roan            C. red X roan      D. roan X roan

E. all of the above crosses would give the same percentage of roan       

 

18. How would one produce a herd of true-breeding roan cattle? (see Q17 for details)

      A. cross roan with roan

      B. cross red with white

      C. cross roan with red

      D. cross roan with white

      E. It cannot be done (A heterozygote cannot be true-breeding)

     

19. Given the parents AABBCc x AabbCc, assume simple dominance and independent assortment.  What proportion of the offspring will be expected to phenotypically resemble the first parent?

      A. ¼ (0.25)            B. ½ (0.5)        C. ¾    (0.75) You need only to look at the C locus      D. 3/8  (0.375)

 

20.  A couple has three children, all of whom have brown eyes and blond hair.  Both parents are homozygous for brown eyes (BB), but one is blond (rr) and the other is a redhead (Rr).  What is the probability that the next child will be a brown-eyed redhead?

      A. ¼          B. ½     brown-eyes is a given; red hair inheritance from Rr x rr)             C. 1/8              D. 1/16             E. 1   

 

 

 

SHORT ANSWER  Each question is worth 4 marks.  Choose 3 to answer.  Answer in pen on a separate sheet of paper. (TOTAL = 12)

 

A. In radishes, two incompletely dominant genes control color and shape. Red and white radishes are homozygous, whereas the hybrid is purple. Long and round radishes are homozygous and if crossed will produce an oval hybrid.  Show the genotypes and phenotypic ratio produced by crossing pure breeding red long radishes with white round radishes.

cross LLRR x L’L’R’R’

all offspring LL’RR’ phenotypically purple and oval

 

B. In parakeets, four different colour patterns are possible. Read the following legend carefully.

 

B_C_  = green colour with black markings

 

B_cc  = blue pigment with black markings

 

bbC_  = yellow pigment with black markings

 

bbcc  =  white (no pigment, no markings)

 

Predict the phenotypic ratio of a cross between two heterozygous green parakeets.

cross BbCc x BbCc  (B_C_ is not the genotype of a heterozygote)

This is a classic dihybrid cross. There will be a 9:3:3:1 ratio (expected outcome)

So 9/16  green/black

3/16  blue/black

3/16  yellow/black

1/16 white

 

C. In cocker spaniels, black colour (B) is dominant over red colour (b). Solid coat colour (E) is dominant over white spotting (e). A solid red male is mated to a black-and-white female. She gives birth to four puppies: one black, one red, one black-and white, and one red-and-white. Show the genotypes of the parents and genotypes for each puppy.

father bbEe     mother Bbee

black puppy BbEe       

red puppy bbEe

black and white Bbee

red and white bbee 

D. In a colony of space tigers, the allele for horizontal stripes (S^H) and the allele for vertical stripes (S^V) are codominant resulting in a plaid tiger when both alleles are present.  Both of these alleles are dominant over spots (s).  Predict the phenotypes and ratios of a cross between a heterozygous vertically striped space tiger and a heterozygous horizontally striped space tiger.   (THINK BLOOD TYPES!)

vertical stripes S^V s     X     horizontal stripes S^H s       

offspring

1 plaid   (S^H S^V) : 1 horizontal stripes (S^H s):  1 vertical stripes S^V s: 1 spotted (ss)       

 

E. A dominant gene, A, causes yellow color in rats. The dominant allele of another independent gene, R, produces black coat color. When the two dominants occur together (A- R-), they interact to produce gray. Rats of the genotype aarr are cream-colored. If a gray male and a yellow female, when mated, produce offspring approximately 3/8 of which are yellow, 3/8 gray, 1/8 cream, and 1/8 black, what are the genotypes of the two parents and the offspring? (Indicate which is which!)

Start with the cream coloured offspring (aarr). The genotype/phenotype is given in the question. Since it’s a double recessive, each parent must possess

(ar).

So the gray male must be AaRr      and the yellow female must be Aarr

¾ will be A_      AND ½ will be R_ (that gives 3/8 AaRr and gray)

                        AND ½ will be rr (that gives 3/8 Aarr and yellow)

¼ will be aa    AND ½ will be R_ ( that gives 1/8 aaRr and black)

                        AND ½ will be rr (that gives 1/8 aarr and cream)

 

 

 

BONUS (answer on this page) 1 mark K or A

 

Make up a really short question (NOT fill in the blank or true/false!) or multiple choice with the correct answer. Maybe something you thought would be on the test but isn’t.  If it’s good, perhaps I’ll sneak it onto the final exam.