Human Genetics Problems

Albinism is a condition in humans in which they are unable to produce the pigment melanin.  People with this condition take on the color of the blood flowing through their capillaries.  This occurs when the dominant normal allele (N) is absent and an individual gets two defective recessive genes (nn).

1)     What phenotype would an individual with the genotype NN be?

2)     What phenotype would an individual with genotype Nn be?

3)     A man heterozygous for albinism has 4 children with an albino woman.  What phenotypic and genotypic ratios would you expect?

Construct a Punnett square:

 NN  : Nn  :  nn                                          Normal  :  Albino

Genotypic ratio:         ___ : ___ : ___          Phenotypic ratio:  _____  :  _____ 

4)     A couple that both have normal skin color have an albino child and 2 normal children.  What are the parents genotypes?

Mother’s Genotype: _____              Father’s Genotype:_____

5)     What are the chances of a couple both hybrid for albinism having 3 normal children?

Construct a Punnett square:

  NN  : Nn  :  nn                                         Normal  :  Albino

Genotypic ratio:         ___ : ___ : ___          Phenotypic ratio:  _____  :  _____

                                                         1st normal    2nd normal     3rd normal

Product Rule (to figure probability):  _______ x _________ x ________ = _________

Most genes that cause abnormal conditions (such as albinism) are recessive.  An exception to this is Chondrodystrophic dwarfism.  It is caused by the presence of a dominant gene (C).  Most people are homozygous recessive (cc) and have normal height.  People that are hybrid or homozygous dominant for the gene are dwarfs with shortened arms and legs, which are usually also very bowed, but their torsos are of normal size.  The dominant gene causes premature closure of the growth plates in the arm and leg long bones.

6)  What are the chances of two normal people having a Chondrodystrophic dwarf child?

Construct a Punnett square:

CC  : Cc  :  cc                                          Dwarf  :  Normal

Genotypic ratio:         ___ : ___ : ___          Phenotypic ratio:  _____  :  _____

            Probability that two normal people will have a dwarf child: _____________  

7)  What are the chances of two heterozygous dwarfs having two normal boys?

Construct a Punnett square:

                                                 CC  : Cc  :  cc                                          Dwarf  :  Normal

Genotypic ratio:         ___ : ___ : ___          Phenotypic ratio:  _____  :  _____

                                        1st boy     1st normal      2nd boy     2nd normal

            Product Rule :  ______ x _________ x _______ x _________ =  _________

Cystic Fibrosis is a disabling genetic disease that used to always cause death by the time a child was a teenager.  Its cause is a recessive gene (g) that produces abnormal glycoproteins that interfere with salt metabolism.  The sweat of the body is high in sodium chloride (table salt), but more important, the mucus secreted is abnormally thick and clogs passageways in the lungs, liver and pancreas.  This leads to pneumonia, and liver function is impaired so bile production is reduced and fat digestion is not normal.  Digestive enzymes from the pancreas are interfered with by fibrous growths.  

8)     What is the genotype of an individual with Cystic Fibrosis?_______

9)     What are the chances of two parents that are heterozygous carriers of the disease having a normal child?

Construct a Punnett square:

 

GG  : Gg  :  gg                                         Normal  :  CF

Genotypic ratio:         ___ : ___ : ___          Phenotypic ratio:  _____  :  _____

Probability of having 1 normal child:_________

10)  What are the chances of two heterozygous (for cystic fibrosis) normal parents having 3 normal children?

                                                           1st normal    2nd normal     3rd normal

Product Rule (to figure probability):  _______ x _________ x ________ = _________

 

11)There is a genetic test now that will allow parents to see if they are carriers of Cystic Fibrosis.  If you found out you and your partner were both carriers, would you choose to have children?  Why or why not?

 GENDER DETERMINATION

12) The male’s sperm is what determines the gender of a child.  Men are XY’s and women are XX’s for the 23 chromosome.  During sperm production the male produces X sperm and Y sperm.  During egg production the female produces only X eggs.  Do a Punnett square that shows why the chances of getting a girl or a boy is ˝ for each (50 50).

Construct a Punnett square:

 

 13)  What are the chances of a couple heterozygous for Chondrodystrophic dwarfism having two normal girls?

                  1st girl      1st normal     2nd girl     2nd normal

Product Rule:  ______ x ________ x ______ x _________ = _________

 14) What are the chances of an albino man and a woman hybrid for albinism having 3 normal boys and then 1 albino girl?  

                      1st boy     normal     2nd boy    normal    3rd girl    albino

Product Rule: ______ x ______ x ______ x _____  x _____ x _____ =________