Expert: Walter Hintz - 12/2/2005

Question
Assignment: human   genetics


Problem # 1:
People with albinism do not produce the pigment melanin.
This is an autosomal recessive disorder.
A couple with normal pigmentation traits has three kids, two with normal pigmentation traits and one with the traits of albinism.
What is the genotype of the parents?


Problem # 2:
Polydactyly is characterized by the presence of extra fingers and (or) toes.
It is an autosomal dominant inheritance pattern.
A women with a normal phenotype and men with polydactyly (heterozygous) want to have a child.
What is the probability for the child to have polydactyly?


Problem # 3:
Hemophilia is characterized by impaired blood clotting ability.
The allele for hemophilia is recessive and carried on the X chromosome.
A women with a family history of hemophilia and a men with no sign of hemophilia want to have a child.
What is the probability for this couple to have a son with hemophilia?
What is the probability for this couple to have a daughter with hemophilia?


Problem # 4:
Some people are unable to convert the amino acid phenylalanine into the amino acid tyrosine.
The buildup of phenylalanine in the body prevents the normal development of the nervous system.
This condition is called phenylketonuria (PKU) and can lead to mental retardation.
PKU is a recessive condition.
IF one parent is heterozygous for PKU and the other parent displays the condition PKU:
What is the probability for their child to have PKU?
What is the probability that their child won’t have PKU?
What are the precautions parents have to take if their child has this condition? (personal research). 3 lines maximum.








Important definitions:

Autosome, dominant , recessive, homozygous, heterozygous, carrier, pedigree chart.


NB:
In a pedigree chart:
the circles represent females
the squares designate males
the horizontal lines symbolize unions
the vertical lines indicate the offspring .


For problem #1 trace the pedigree chart.
For problem # 2, 3 and # 4 complete a Punnett square.

For each problem, the phenotypes [in between brackets] and the genotypes ( two alleles) must be clearly indicated.
The student must present the reasoning that lead to his answer.
The answer alone won’t be sufficient.

Answer
#1 Both parents are heterozygous normal
     Father ______________-________ Mother

      child (n)       Child (n)      child (albino)
   I cannot make boxes and circles with a computer

#2 Let P = Normal
      p - poly
            Pp   X PP
      P         p

 P  PP         Pp   50% with it


 P  PP         Pp  

#3 Let Xh = hemo
      X  = normal
 If mom is a carrier then
  XhX   x  XY               

     Xh             X

X  XXh             XX  All sons have it: no daugthers do

Y   XhY            XhY

   If Mom s not a carrier no children can have it

#4  Let P = normal
       p = PKU

    pp    x   Pp

      p            p
                        1/2 have it
   P Pp           Pp           

   p  pp          pp    

      Look uo PKU at google