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Post-Lab Questions: Heredity (Exercise 13)

You must show how you worked out the problems to get credit.

1.     Explain the implications of Mendel's law of segregation as it applies to the distribution of alleles in gametes.

 

 

 

2.     Assume that a single gene controls the production of hairs on a plant's leaves with two alleles, H (dominant) and h (recessive).  Hairy leaves are dominant to smooth (nonhairy) leaves.

 

 

a.     Name the genotype(s) of a smooth-leaved plant.                                

b.     Name the genotype(s) of a hairy-leaved plant.                        

c.     What are the possible genotypes of gametes produced by the smooth-leaved plant?                                      

d.     What are the possible genotypes of gametes produced by the hairy-leaved plant?                                      

 

3.     In fruit flies, red eyes (R) are dominant over purple eyes (r).  Two red-eyed fruit flies were crossed, producing the following offspring: 76 red-eyed flies and 24 purple-eyed flies.

 

 

a.     What is the approximate ratio of red-eyed to purple-eyed flies?                     

b.     What are the parents' genotypes?                              

c.     What is the genotypic ratio of the F1 offspring?                                 

d.     What is the phenotypic ratio of the F1 offspring?                               

 

4.     Petunia flower color is governed by two alleles, but neither allele is truly dominant over the other.  Petunias with the genotype RR are red-flowered, those that are heterozygous (Rr) are pink, and those with the rr genotype are white.  This is an example of incomplete dominance.

 

 

 

a.     If a white-flowered plant is crossed with a red-flowered petunia, what is the genotypic ratio of the F1 offspring?                            

b.     What is the phenotypic ratio of the F1 offspring?                               

c.     If two of the offspring are crossed, what phenotypes will appear in the F2 generation?

d.     What will be the genotypic ratio in the F2 generation?

 

 

5.  In humans, sex is determined by special sex chromosomes.  An individual containing two X chromosomes (XX) is female, while an individual with an X and a Y chromosome (XY) is male.  The sex chromosomes bear alleles for traits, just like other chromosomes.  Genes that occur on the sex chromosomes are said to be sex-linked.  More genes are present on the X chromosome than are found on the much shorter Y chromosome.  A gene associated with the X chromosome that is not found on the Y chromosome is X-linked (not found on Y chromosome).  In humans, color vision and hemophilia (a blood disorder) are X-linked.

Normal color vision (XN) is dominant over color-blindness (Xn).  Suppose a normal vision man fathers the children of a normal-vision woman whose father was color-blind.

 

 

 

 

 

a.  What proportion of the daughters will be colorblind?                                

b.     What proportion of the sons will be colorblind?                                      

c.     If the father of these children were colorblind, would there be any chance of producing normal-vision sons?                        

 

 

6.  The major blood groups of humans are determined by multiple alleles; that is, there are more than two possible alleles, any one of which can occupy a particular locus on a chromosome.  In the ABO blood group system, a single gene can exist in any of three allelic forms: A, B, or O.  Alleles A and B code for the production of antigen (a protein) A and antigen B respectively on the surface of red blood cells.  A and B are codominant (equally dominant and together would give the phenotype AB), while the O is recessive (you would need OO to give a phenotype of O).  The genotype AO shows the phenotype A (A type blood) and the genotype BO shows the blood type B.

 

In a case of a disputed paternity, the child is type O and the mother is type A.  Could an individual of the following blood types be the father?   Explain each possibility.

 

a.  O                                                                                                               

b. A                                                                                                                

c.  B                                                                                                                

d.  AB                                                                                                                                                                                                                                     

 

 

 

 

 

 

7.      Now for a two-trait (dihybrid) problem!  Use your lab exercise to determine dominant and recessive alleles.  A pigment-eyed, dimple-chinned man marries a blue-eyed woman without a dimpled chin.  Their first-born child is blue-eyed and has a dimpled chin.

 

 

 

a.     What are the possible genotypes of the father?                                  

b.     What genotype is the mother?                                    

c.     What alleles may have been carried by the father's sperm?                             

 

8.      Suppose a dimple-chinned, blue-eyed man whose father lacked dimples marries a woman who is homozygous recessive for both traits.

 

 

 

 

a.     What is the expected genotypic ratio of children produced by this marriage?                                                

b.     What is the expected phenotypic ratio?                                                          

 

 

 

9.     In his original work on garden peas, Mendel found that yellow seed color (YY, Yy) is dominant over green seeds (yy) and that round seed shape (RR, Rr) is dominant over shrunken seeds (rr).  Mendel crossed pure-breeding (homozygous) yellow, round-seeded plants with green, shrunken-seeded plants.

 

 

a.     What will be the genotype and phenotype of the F1 produced from such a cross?

                                                     i.     Genotype                                                        

                                                      ii.     Phenotype                                                      

 

 

b.     If the F1 plants are crossed, what will be the expected phenotypic ratio of the F2 generation?

 

(You may use the back of this sheet to work this problem.)

 

                                                     i.     Phenotypic ratio                                                         

 

10.  Black color is dominant over white color in mice.  You are given a black mouse and there is some question whether the mouse is homozygous or heterozygous.  How will you find out?