GENETIC PROBLEMS
CHAPTER 13
Mendelian Monocross
1.
Black coat color in guinea pigs is dominant over white coat color.
a. By means of a Punnett Square, show the results of crossing a hybrid black with a
pure white.
b. Show the results of crossing a pure black with a hybrid.
c. Show the results of crossing a hybrid black with a homozygous white.
Mendelian Monocross
2.
A black guinea pig was crossed with a white guinea pig. All of the individuals in the F 1
generation were black. These individuals were then crossed among themselves,
resulting in 30 black guinea pigs and 10 white guinea pigs.
a. How many of the black pigs in the F2 generation would be pure dominant? hybrid?
recessive?
b. How many of the white pigs in the F2 generation would be pure dominant? hybrid?
recessive?
Mendelian Monocross for Test Cross Application
3.
Explain with the aid of Punnett square how you would determine whether a squirrel is
pure gray or hybrid gray. (gray is dominant over black) This is a test cross problem and
one parent is unknown dominant and one parent is homozygous recessive.
Mendelian Monocross for Application
4. In cattle, the hornless or polled condition is dominant. A certain polled bull is bred to
three cows. With cow A, who has horns, a polled calf is produced. With cow B, also
with horns, a horned calf is produced. With cow C, who is polled, a horned calf is
produced. What are the genotypes of the bull and the three cows?
Mendelian Dihybrid Pedigree
5. A blue-eyed man, both of whose parents were brown-eyed, marries a brown-eyed
woman whose father was brown-eyed and whose mother was blue-eyed. They have
one blue-eyed child. What are the genotypes of all the individuals mentioned? (brown
is dominant over blue)
Mendelian Dihybrid Pedigree
6.
A right handed, blue eyed man whose father was left-handed marries a left-handed,
brown-eyed woman from a family in which all the members have been brown-eyed for
several generations. What offspring may be expected from this marriage in regard to
the two traits mentioned? State the probability for each phenotype (right-handedness
is dominant)
Mendelian Trihybrid
7.
In garden peas, tall vine (T) is dominant over dwarf (t), green pods (G) over yellow (g),
and round seed (R) over wrinkled seed (r). If a homozygous dwarf, green, wrinkled
pea plant is crossed with a homozygous tall, yellow, round one, what will be the
appearance of the F1? What gametes does the F1 form? What is the appearance of
the offspring of the cross of the F1 with its dwarf, green, wrinkled parent?
Exception- Incomplete Dominance (Blending)
8.
After several matings of tan colored birds, the following offspring resulted: 23 white,
26 brown, 53 tan. By means of Punnett Squares show each of the following:
a. a cross that would produce 50% of all offspring, brown
b. a cross that would produce 100% of all offspring tan
Exception- Incomplete Dominance (Blending)
9.
There are three types of radishes: round,oval, and long. A breeder makes three
crosses and obtained the results indicated below. Using diagrams, show the crosses
in each
a. first cross: long with round gave 342 oval
b. second cross: long with oval resulted in 48 long and 52 oval
c. third cross: oval with round resulted in 141 oval and 137 round
Exception – Multiple Alleles and Incomplete Dominance (Co- Dominance)
10. List the possible genotypes for people with each of the following blood types: A, B,
AB, O
Exception – Multiple Alleles and Co- Dominance
11.
Hospital mix up: Two boys, baby #1 has blood type O and baby #2 has blood type A,
one set of parents are both type A and the other set have types AB and O. Match the
baby with its parents.
Exception-Sex Linkage and Pedigree
12.
Hemophilia is a sex-linked heterozygous condition. Show each cross and the offspring
using Punnett Squares.
a. cross a carrier girl with a normal male
b. cross a homozygous dominant female with a hemophiliac male
c. cross a normal female whose father had hemophilia with a normal male
d. cross a hemophiliac female with a normal male
Exception-Sex Linkage and Pedigree
13. A brown eyed colorblind man whose mother was normal color vision and blue eyed
married a blue eyed girl with normal color vision whose father was colorblind. Give
their genotypes and show the possible children of this marriage. (colorblind is a
recessive sex-linked trait)
Application
14.
A man sues his wife for divorce on the ground of infidelity. Both the man and his wife
have normal eyes, but there is a baby daughter who has “columbo iridis”, a fissure of
the iris of the eye. This characteristic is known to be inherited on the X chromosome
as a recessive allele. If you were the man’s lawyer, could you use this fact as
evidence? If so, how would you explain the case to the jury? Prove your answer with
a pedigree.
Application Autosomal vs Sex LInkage
15.
In Drosophila, when cut winged males are mated with normal homozygous females, all
the flies are normal. When these flies are crossed among themselves, one-half of the
males have cut wings. Show by diagrams whether or not cut wings are autosomal or
sex-linked.
Human Chromosome facts
16.
_____X chromosomes in egg cell
_____ X chromosomes in sperm cell
_____autosomes in nose cell
_____autosomes in egg cell
_____Y chromosomes in sperm cell
_____pairs of autosome in male skin