Genetics Practice Problems: Mendelian Genetics
1. Pattipan squash are either white or yellow. You start growing pattipans and find out that if you want to get white pattipans then at least one of the parents must be white. Which color is dominant?
2. True-breeding tall red-flowered plants are crossed with dwarf white flowered plants. F1 generation consists of all tall pink-flowered plants. Assuming that height and flower color are each determined by a single gene locus, predict the results of an f1 cross of the TtRr plants. List the phenotypes and predicted ratios for the F2 generation
3. Blood typing has often been used as evidence in paternity cases, when the blood type of the mother and child may indicate that a man alleged to be the father could not possibly have fathered the child. For the following mother and child combination, indicate which blood groups of potential fathers would be exonerated in court.
Blood group of mother / Blood group of child / Exonerated blood group (s)AB / A / ?
O / B / ?
A / AB / ?
O / O / ?
B / A / ?
4. In rabbits, CC = normal; Cc = deformed legs, cc = lethal
BB = black coat color; Bb = brown coat color, bb = white coat color
What are the phenotypic ratios of offspring from a deformed-leg, brown rabbit and a deformed-leg, white rabbit
5. Fur color in rabbits is determined by a single gene locus for which there are four alleles. Four phenotypes are possible: black, Chinchilla (gray color caused by white hairs with black tips), Himalayan (white with black patches on extremities of rabbit), and white. The black allele (C) is dominant over all other alleles, Chinchilla (Cch) is dominant over Himalayan (Ch), and white © is recessive to all others.
- A black rabbit is crossed with a Himalayan, and the F1 consists of a ratio of 2 black: 2 Chinchilla. What are the possible genotypes of the parents?
- A black rabbit is crossed with a Chinchilla rabbit. The F1 ratio was 2 black: 1 Chinchilla : 1 Himalayan. From these results determine which genotypes the parents
6. For the following crosses, determine the probability of obtaining the indicated genotype in an offspring
Cross / Offspring / ProbabilityAAbb x AaBb / AAbb
AaBB x AaBb / aaBB
AABbcc x aabbCC / AaBbCc
AaBbCc x AaBbcc / aabbcc
7. A man who has type O blood has a child with a woman who has type A blood. The woman’s mother has AB blood, and her father, type O. What is the probability that the child has each of the following blood types? a. O b. A c. B d. AB
8. Polydactyly (extra fingers and toes) is due to a dominant gene. A father is polydactyl, the mother has the normal phenotype, and they have had one normal child. What is the genotype of the father? Of the mother? What is the probability that a second child will have the normal number of digits
9. Achondroplasia is a common form of hereditary dwarfism that causes very short limbs, stubby hands, and an enlarged forehead. Above are four pedigrees depicting families with this specific type of dwarfism. What is the most likely mode of inheritance? Cite a reason for your answer.
10. Caleb has a double row of eyelashes, which he inherited from his mother as a dominant trait. His maternal grandfather is the only other relative to express the trait. Veronica, a woman with normal eyelashes, falls madly in love with Caleb, and they marry. Their first child, Polly has normal eyelashes. Now Veronica is pregnant again and hopes they will have a child who has double eyelashes. What chance does a child of Veronica and Caleb have of inheriting double eyelashes? Draw a pedigree of this family.