Graded Mendelian Genetics (Punnett square) Homework - Bio I
(30 points)
Directions: You must support all answers with a Punnett square or some explanation
for full credit. One point is awarded for the Punnett square in each question. No
credit for the question if there is no Punnett square!!!
Name:_____________________________________
Date: ________________________________
1.
(3 pts) PKU stands for phenylketonuria, which is the inability to recognize and
process the amino acid phenylalanine.
PKU is an inherited disease caused by a recessive gene. If a mother and father are
both carriers for the disease:
What is the probability of producing a child with PKU? ______________
What is the probability of producing a child that has the gene and can pass it on (a
carrier/no disease) ? ___________________________________
2. (3 pts) A rooster with gray feathers is bred with a hen with gray feathers. The
resulting chick colors are 15 gray, 6 black, and 8 white.
What would you call this pattern of inheritance?______________________
What color outcomes would you expect if a gray feathered rooster was bred with a
pure-breeding black feathered hen? (give percents of each color)
___________________________________________________
3. (2 pts) Green (G) is dominant in peas. Yellow (g) is recessive. What are the
genotypes of the P1 generation if the F1 generation is about 75% green and 25%
yellow? ___________________ Draw the square.
4. (4 pts) Polydactly (extra digits) is a dominant trait. Anne Boleyn, the second wife of
Henry VIII , had 11 fingers. Henry VIII had the usual number. Anne and Henry only
had one child, Elizabeth I, who had the normal number of fingers.
What is Ann Boleyn’s genotype?________________________
Did one of her parents have to have extra digits? _____________
What is the probability that Anne and Henry would have a child with extra
digits?_____________________
5. (2 pts) If both parents have heterozygous Type A blood, what is the percent chance
that they will produce a child with Type O blood? ____________
(Draw the square and write blood type in each square)
6. (2 pts) If both parents have Type AB blood, what are the possible blood types for
their children. Draw the Square.
7. (2 pts) If the mother is heterozygous Type B and has three children with Type A,
Type O, and Type AB, what is the father’s blood type? Draw the square.
8. (5 pts) Cleft chin and Unibrow are both single gene traits with clear dominantrecessive inheritance. (Unibrows and cleft chins are both dominant.) (check the
website if you forget how to do a dihybrid cross!) (show your math - neatly - so you
can partial credit if you make a math error!)
If a mother who is heterozygous for cleft chin and has no unibrow has a child with a
man who has no cleft chin and is homozygous dominant for unibrow, what is the
probability that they will:
- have a child with a cleft chin and a unibrow?_________________
- have a child with no cleft chin and no unibrow? ______________
- have a child with no cleft chin and a unibrow? ________________
9. (5 pts) Curly hair shows incomplete dominance over straight hair, and attached
earlobes is dominant to unattched earlobes.
If a wavy-haired, homozygous for attached earlobe mother has a child with a
straight-haired, unattached earlobe father, what is the probability that they will
have:
- a wavy-haired child with attached earlobes?___________________________
- a straight-haired child with unattached earlobes? ___________________
10. (1 pt) . The ratio 9:3:3:1 is a “classic” (unchanging!) ratio for what kind of cross in
Mendelian genetics?
a. a homozygous- heterozygous cross
b. a heterozygous dihybrid cross
c. a pure-breeding dominant-recessive cross
d. a pure-breeding recessive cross
11. What do the numbers in the 9:3:3:1 ratio mean exactly? (9 what? 3 what? 3 what? 1
what?