One Gene Pair ANSWERS

B.                GENERAL RULE  ---  A single pair of genes usually controls a  S I N G L E  trait,
but here's another exceptions to this "rule."

(2)   Sometimes a S I N G L E  pair of genes can influence more than one trait.

Example #1 follows:

 

   (a)   Example 1 -- In certain mice, the gene
          for yellow fur is dominant
          (symbol =  Y) to that for the recessive
          gene for gray fur (symbol = y). 
          If two heterozygous  yellow mice are
          bred, what is the expected outcome
          (color ratio) (PHENOTYPE) of their
          offspring?

          To answer this, complete the following
          Punnett Square::
                            Mom
                         Y     y
                                                                                                Y  YY  Yy
                                                                             Dad             y   Yy   yy

                                                                        
You would expect  _3_ yellow mouse/mice (All the YY's and Yy's): _1_ gray mouse/mice. 

Surprise!  The actual obtained data in  L A R G E  numbers of matings is approximately  2 yellow: 1 gray.   Other experiments showed that all the yellow offspring mice were heterozygous (Yy).  This is not what we predicted in the Punnett Square. 

From the Punnett Square, which genotype in real life is missing?   Answer =   Y  Y . 
It turned out that the missing mice had never been born; the mother had miscarried
ALL of them.   The dominant gene (allele) symbol Y controls  _2_  (a number) trait(s)
in these mice.

            ((1))  The heterozygous condition (genes _Y_ _y_) produces _yellow_  fur
            ((2))  The homozygous condition, (genes _Y_ _Y_) is a L E T H A L   gene 
                     (ask Mel & Danny if you don't know this word!)   Lethal Weapon of course!

Example #2 Follow:

The trait for lack of skin pigmentation is known as  A L B I N I S M.  You probably are
more familiar with the other noun  A L B I N O  which is an organism which lack such
pigmentation.   This G E N E     M U T A T I O N  occurs in many species, although it is
rare in most of these species.  Sometimes humans artificially select these non-pigmented
organisms for breeding to have an entire race of them.   Here are some examples of albinos
in many species.  You must name the species for each photo.

           a)  Cutie here is a  lab   R A T (not canary!)

  

    b)  This is a WHITE TAILED- D E E R,
         but who can tell since we can't see
         the tail and the whole organism is
         now white.

 

        c)    And this is an albino  P E N G U I N

 

 

 

 

 

        d)   Puppy Power!   Some dog breeds are selected because
                                                        they are all albinos. 

 

 

 

 

And humans are not exempt either.   Here's a collection of human albinos.

... I deleted the images to save space (the final frontier!)

Look for the two different similarities in many of the albinos pictured above. 

(b)  Example 2  --  In humans a person who is homozygous for the two gene for albinism
       lacks two separate distinct traits.  Most of these people lack both the trait for adequate 
       P I G M E N T A T I O N   and lack good  E Y E S I G H T.   As stated before, this is
       the results of   O N E   gene which controls  T W O   traits.   

(3)    A human cell contains many thousands of different genes in its chromosomes found in
 its N U C L E U S.