A cross of F1 hybrid with either of the two parents is known as back cross.When F1 off springs are crossed with the dominant parents all the F2 off springs developdominant character.On the other hand when F1 hybrids are crossed with recessive parent, individuals with both the phenotypes appear in equal proportions. While both the crosses areknown as backcross, the second one is specified as test cross.

**Back cross**

The correct answer is option 'B' - Back cross.

**Explanation:**

A back cross is a type of genetic cross between an F1 individual and one of its parents. It involves crossing the hybrid offspring (F1) with one of the two parental lines to reintroduce specific traits from the parent into the hybrid population. This type of cross is commonly used in plant and animal breeding to enhance desired characteristics or to study inheritance patterns.

**Procedure of Back Cross:**

1. Select the F1 individual: The F1 individual is the result of a cross between two different parental lines. It exhibits a combination of traits from both parents.

2. Choose one of the parents: In a back cross, one of the two parents is selected to cross with the F1 individual. This parent is chosen based on the specific traits that need to be reintroduced into the hybrid population.

3. Cross the F1 individual with the selected parent: The selected parent is crossed with the F1 individual to produce offspring that inherit specific traits from the parent. This is typically achieved through controlled pollination in plants or controlled mating in animals.

4. Analyze the offspring: The resulting offspring from the back cross are examined to determine if the desired traits have been successfully reintroduced. If the traits of interest are present in the offspring, it indicates a successful back cross.

**Significance of Back Cross:**

1. Trait enhancement: Back crosses allow breeders to introduce specific traits from one parent into the hybrid population, thereby enhancing the desired characteristics of the offspring.

2. Understanding inheritance patterns: By performing back crosses, researchers can study the inheritance patterns of certain traits and gain insights into the genetic basis of those traits.

3. Genetic diversity preservation: Back crosses can also be used to preserve genetic diversity by crossing hybrids with their original parents. This helps to maintain a wide range of genetic traits within a population, which is important for long-term survival and adaptability.

In summary, a back cross involves crossing an F1 individual with one of its parents to reintroduce specific traits from the parent into the hybrid population. It is a useful breeding technique for enhancing desired characteristics and studying inheritance patterns.

Backcrossing is the crossing of a hybrid with one of its parents or an individual genetically similar to its parent in order to achieve offspring with a genetic identity which is closer to that the of the parent. It is used in horticulture of gene knockout organisms