Hi folks,
You will only learn this material by solving problems. You will find some problems in your textbook p258-259.
In addition, I like you to study the following problems:
(1) Coat color in rabbits is determined by 4 alleles: C (gray), C ch (chinchilla), C h (Himalayan), and c
(albino). C>C ch >C h >c (a) What are the possible genotypes of a gray-colored, chinchilla,
Himalayan, and albino rabbits? What is the cross that resulted in a litter of 50% gray and 50%
Himalayan?
(2) What is the probability of obtaining an offspring of phenotype aaB-ccD-ee in a penta-hybrid cross? In the corresponding test cross?
(3) In horses coat color has two co-dominant alleles so that animals can be sorrel, roan, or white.
What cross yields 50% roan and 50% white offspring?
(4) The co-dominant alleles of the feather color traits are black and white. Heterozygous animals express white and black in the same feathers and are called silver. What cross yields only black animals? Only white? Only silver? And 50% black and 50% silver?
(5) Alcohol dehydrogenase protects honeybees from alcohol intoxication. The two co-dominant alleles are separated during electrophoresis because one allele (A f ) migrates fast and the other
(A s ) slow in an electric field. Draw the electrophoretogram of the parents and offspring of a monohybrid cross.
(6) Jimson weed can be round, oval or long and smooth, fuzzy, or spiked. What is the probability for obtaining oval, fuzzy fruit in a hybrid cross?
(7) In Roses flower color is determined by two traits. In the presence of “A” white (no color) is converted to pink which, in turn, is converted to red in the presence of “B”. “a” and “b” are the corresponding inactive alleles. (a) Explain why roses can only be white, pink, or red. (b) What is the phenotypic ratio of white, pink, and red roses among the offspring of the hybrid cross? (c) of the test cross?
(8) A trait such as length is caused by 5 traits. Each trait has a dominant allele that contributes to the length of the plant and an alternative form that does not. How many length classes are there in the population? What is the most frequent length class? What is the genotype of the longest individuals? Of the shortest individuals?
(9) A cross of two chickens each with a Walnut comb yields 9 chicks with a Walnut comb, 3 chicks with a Pea comb, 3 chick with a Rose comb, and 1 animal with a Single comb. What is the genotype of the parents?
(10) What is the proportion of feathered and non-feathered chickens in a dihybrid cross when feathering is determined by two traits?
(11) Black Labradors carry at least one copy of the “B” and “E” allele, whereas chocolate animals are homozygous recessive for the B-trait (bb) and yellow offspring are homozygous for the E-trait
(ee). (a) Determine the proportion of offspring that will be black, chocolate, and yellow in a testcross. (b) A black animal is crossed with a homozygous recessive male. Half of the pups are black and half are chocolate. What is the genotype of the parents?

(12) Coat color in cats is determined by two traits. The “A” causes a fawn-colored fur against which black markings are distinct. In contrast, the aa animal has a solid black background. The ”T” allele determines black striped markings and the “t” allele causes black spots instead (T>t). (a)
Why are there only striped, spotted, and black cats? (b) What cross yields striped, spotted, and black kittens in a ratio 9:4:3? What cross yields striped, spotted, and black kittens in a ratio
1:1:2?
(13) In guinea pigs agouti (banded hair) > black and color > white. Write the genotype of agouti, black, and white animals. What cross yields 9 agouti, 3 black, and 4 white animals? What cross yields 25% agouti, 25% black, and 50% white animals?
(14) The shape of squash fruit can be long, round, or disc shaped. A cross of two disc shaped plants yields 1 long, 6 round, and 9 disc shaped offspring. Explain the cross. What is the proportion of disc, round, and long offspring of the test cross?
(15) Cucumber fruit can be white, green, or yellow. The dominant allele A prevents all color formation and resulting fruit is white. B is required to convert green to yellow. Explain how to white parents can yield offspring with white (12), yellow (3), and green (1) fruit.
(16) A dominant gene, A, causes yellow color of rats. The dominant allele of another independent gene, R, produces black coat color. When the two dominant genes occur together (A-B-), they interact to produce grey coat color. Rats of the double recessive genotype are cream colored. If a grey male and a yellow female are mated and produce 3/8 yellow, 3/8 grey, 1/8 cream, and
1/8 black offspring, what were the genotypes of the parents?
Good luck!
Dr. B.