GENETICS PROBLEMS
OBJECTIVE

Solve monohybrid and dihybrid cross problems;
PROBLEMS
1.
Complete the following table:
Organism
Chromosomes in
Haploid Cells
Chromosomes in
Diploid Cells
Ascaris megalocephala
1
2
Drosophila melanogaster
Onion
8
Homologous
Chromosomes/Cell
4
8
Pea
7
Domestic cat
19
Man (sperm cell)
23
Dog
39
2. There are 40 chromosomes in somatic cells of the house mouse.
a. How many chromosomes does a mouse receive form its father?
b. How many autosomes (non-sex chromosomes) are present in a mouse gamete?
c. How many sex chromosomes are in a mouse ovum?
d. How many autosomes are in somatic cells (cell of the body / not a gametic cell) of a
female?
3. Assume the horse has a diploid complement of 64 chromosomes and the ass has 62
chromosomes.
a. Predict the number of chromosomes to be found in the hybrid offspring, called a mule,
produced by mating a male ass to a female horse.
b. What is the maximum number of tetrads (Homologous Pairs) that could theoretically
form during first meiotic prophase in the mule?
4.
A plant of genotype AABbCC is crossed with an AaBbCc plant. What is the probability
of an offspring having the genotype AABBCC?
8. A Heterozygous black (Bb) guinea pig is mated to homozygous recessive (bb) white. Predict
the genotypic and phenotypic ratios expected from crossing the black F1 progeny (offspring)
to
a. The black parent
b. The white parent
1
9. A dominant gene W produces wire-haired texture in dogs; its recessive allele w produces
smooth hair. A group of heterozygous wire-haired individuals are crossed and their F1
progeny are then test crossed. Remember to only test cross if the genotype is unknown.
Determine the expected genotypic and phenotypic ratios among the testcross progeny.
10. The Palomino horse is a hybrid exhibiting a golden color with lighter mane and tail. A pair
of Incomplete dominant alleles (D and Dl) is known to be involved in the inheritance of
these coat colors. Genotypes homozygous for the D allele are chestnut colored (reddish),
heterozygous genotypes are Palomino colored, and genotypes homozygous for the Dl allele
are almost white and called cremello.
a. From matings between Palominos, determine the expected Palomino: non-Palomino
ratio among the offspring.
b. What percentage of the non-Palomino offspring will breed true?
c. What kind of mating will produce only Palominos?
11. A man of blood group B is being sued by a woman of blood group A for paternity. The
woman's child is blood group O.
a. Is this man the father of this child?
b. If this man actually is the father of this child, specify the genotype of both parents.
c. If it was impossible for this group B man to be the father of a type O child, regardless of
the mother's genotype, specify his genotype.
d. If a man was blood group AB, could he be the father of a group O child?
2
12. Plumage color in mallard ducks is dependent upon a set of three alleles: MR for restricted
mallard pattern, M for mallard, and m for dusky mallard. The dominance hierarchy is
MR>M>m. Determine the genotypic and phenotypic ratios expected in the F1 from the
following crosses:
a. MRMR x MRM
b. MRMR x MRm
c. MRM x MRm
13. Coat colors of the Shorthorn breed cattle represent a classical example of codominant
alleles. Red is governed by genotype RR, roan (mixture of red and white) by RW, and white
by WW.
a. When roan Shorthorns are crossed among themselves, what genotypic and phenotypic
ratios are expected among their progeny?
b. If red Shorthorns are crossed with roan, and the F1 progeny are crossed among
themselves to produce F2, what percentage of the F2 will probably be roan?
14. The absence of legs in cattle (amputated) has been attributed to a completely recessive
lethal gene. A normal bull is mated with a normal cow and they produce an amputated calf
(usually dead at birth). The same parents are mated again.
a. What is the chance of the next calf being amputated?
b. What is the chance of these parents having two calves, both of which are amputated?
15. Thalassemia is a hereditary disease of the blood of man resulting in anemia. Severe anemia
(thalassemia major) is found in homozygotes (TMTM) and a milder form of anemia
(thalassemia minor) is found in heterozygotes (TMTN). Normal individuals are homozygous
(TNTN). If all individuals with thalassemia major die before sexual maturity:
a. What proportion of the adult F1 from marriages of thalassemia minor by normals would
be expected to be normal?
b. What fraction of the adult F1 from marriages of minors by minors would be expected to
be anemic?
16. A red-green color-blind man marries a normal woman. From this union one color-blind
daughter is born. Give the genotypes of these three people. List the genotypes of all
possible offspring from this marriage.
3
17. Two pedigrees are given in verbal form below. Convert each of these pedigrees into a
diagram.
a. An albino woman, the daughter of normal parents and the sister of four normal
brothers, marries a normal man. They produce eight boys and five girls, all normal.
b. A normal man whose parents and grandparents were normal marries a normal woman
whose parents and grandparents were normal. From this union come one albino girl,
one normal girl, and one normal boy.
4