Compare and contrast the following terms:

dihybrid cross and trihybrid cross

For the cross Aabb×aaBb, what is the expected genotype ratio? What is the expected phenotype ratio?

Determine whether the statements below are true or false. If a statement is false, provide the correct information or revise the statement to make it correct.

If a dihybrid  plant is self-fertilized,
(1) 9/16 of the progeny will have the same phenotype as the F₁ parent.
(2) 1/16 of the progeny will be true-breeding.
(3)  1/2 of the progeny will be heterozygous at one or both loci.

Determine whether the statements below are true or false. If a statement is false, provide the correct information or revise the statement to make it correct.

If a dihybrid cross is performed, the expected genotypic ratio is 9:3:3:1.

In tomato plants, the production of red fruit color is under the control of an allele R. Yellow tomatoes are rr. The dominant phenotype for fruit shape is under the control of an allele T, which produces two lobes. Multilobed fruit, the recessive phenotype, have the genotype tt. Two different crosses are made between parental plants of unknown genotype and phenotype. Use the progeny phenotype ratios to determine the genotypes and phenotypes of each parent.

  Cross 1 progeny:          3/8 two-lobed, red
                                        3/8 two-lobed, yellow
                                        1/8 multilobed, red
                                        1/8 mutlilobed, yellow
  Cross 2 progeny:           1/4 two-lobed, red
                                         1/4 two-lobed, yellow
                                         1/4 multilobed, red
                                         1/4 multilobed, yellow

In chickens, the presence of feathers on the legs is due to a dominant allele (F), and the absence of leg feathers is due to a recessive allele (f). The comb on the top of the head can be either pea-shaped, a phenotype that is controlled by a dominant allele (P), or a single comb controlled by a recessive allele (p). The two genes assort independently. Assume that a pure-breeding rooster that has feathered legs and a single comb is crossed with a pure-breeding hen that has no leg feathers and a pea-shaped comb. The F₁ are crossed to produce the F₂. Among the resulting F₂, however, only birds with a single comb and feathered legs are allowed to mate. These chickens mate at random to produce F₃ progeny. What are the expected genotypic and phenotypic ratios among the resulting F₃ progeny?

Alleles of the IGF-1 gene in dogs, encoding insulin-like growth factor, largely determine whether a domestic dog will be large or small. Dogs with an ancestral dominant allele are large, whereas dogs homozygous for the mutant recessive allele are small. Chondrodysplasia, a short-legged phenotype (as in dachshunds and basset hounds), is caused by a dominant gain-of-function allele of the FGF4 gene. The MSTN gene encodes myostatin, a regulator of muscle development. Dogs with a dominant ancestral allele of the MTSN gene have normal muscle development, while dogs homozygous for recessive mutants in the MTSN gene are 'double muscled' and have trouble running quickly. However, dogs heterozygous for the mutant allele run faster than either of the homozygotes.
You breed a pure-breeding small basset hound of normal musculature with a pure-breeding 'bully' whippet, a double-muscled large dog with normal legs.

If the F₁ of this cross is interbred, what proportion of the F₂ are expected to be fast runners and what proportion normal-speed runners?

Alleles of the IGF-1 gene in dogs, encoding insulin-like growth factor, largely determine whether a domestic dog will be large or small. Dogs with an ancestral dominant allele are large, whereas dogs homozygous for the mutant recessive allele are small. Chondrodysplasia, a short-legged phenotype (as in dachshunds and basset hounds), is caused by a dominant gain-of-function allele of the FGF4 gene. The MSTN gene encodes myostatin, a regulator of muscle development. Dogs with a dominant ancestral allele of the MTSN gene have normal muscle development, while dogs homozygous for recessive mutants in the MTSN gene are 'double muscled' and have trouble running quickly. However, dogs heterozygous for the mutant allele run faster than either of the homozygotes.
You breed a pure-breeding small basset hound of normal musculature with a pure-breeding 'bully' whippet, a double-muscled large dog with normal legs.

What are the genotypes and phenotypes of the F₁ puppies?

Assume you have mated a homozygous dominant purple, square plant with a homozygous recessive pink, spherical plant. What is the proportion of purple and spherical plants that would be produced in the F₂ generation? 

Write out all of the following gametes that can be produced from individuals with the following genotypes. 

a. AaBB 

b. AaBb 

c. AaBbCc 

d. AaBbcc

Two organisms with the genotypes Aa bb Cc Dd Ee and Aa Bb Cc dd Ee were crossed. Use the branch method to determine the proportion of the following genotypes in the offspring. I. aa bb cc dd ee

Two organisms with the genotypes Aa bb Cc Dd Ee and Aa Bb Cc dd Ee were crossed. Use the branch method to determine the proportion of the following genotypes in the offspring. II. Aa bb Cc dd ee

Two organisms with the genotypes Aa bb Cc Dd Ee and Aa Bb Cc dd Ee were crossed. Use the branch method to determine the proportion of the following genotypes in the offspring. III. AA BB CC Dd ee

In melons, spots (S) are dominant to no spots (s) and bitterness (B) is dominant to sweet (b). Answer the following questions that arise from a crossing of a homozygous dominant plant with a homozygous recessive plant. Assume Mendelian inheritance. I. What is the F2 phenotypic ratio if the F1 generation is intercrossed?