Question

The second-generation offspring of a cross between individuals who are homozygous for different alleles of a gene are called the _____. a. \(\mathrm{F}_{1}\) generation c. hybrid generation b. \(\mathrm{F}_{2}\) generation d. none of the above

Short answer

The answer is (b) F_{2} generation.

Step-by-step solution

Understanding the Generations

In genetics, the parental generation is often referred to as the P generation. When two individuals who are homozygous for different alleles of a gene are crossed, their offspring are known as the first filial or F_{1} generation. This generation is typically heterozygous for the alleles.

Identifying the Second Generation

The second filial generation, or F_{2} generation, is produced by inter-breeding individuals of the F_{1} generation. This occurs when the F_{1} individuals are allowed to self-pollinate or are crossed with each other.

Answering the Question

In the given question, the second-generation offspring after the initial cross are referred to as the F_{2} generation. Therefore, the correct answer is (b) F_{2} generation.

Key concepts

F1 Generation

In Mendelian genetics, the F1 generation refers to the first group of offspring produced from a cross between two parental organisms. These parents are typically homozygous for different alleles, meaning they have two identical alleles, but each parent has a different version of a particular gene.

When these parents are crossed, the resulting offspring make up the F1 generation. These offspring are often heterozygous. This means they inherit one allele from each parent, resulting in differing alleles for the genes in question.

• Example: If one parent is homozygous dominant (AA) for a trait and the other is homozygous recessive (aa), all F1 offspring will be heterozygous (Aa).
• The F1 generation commonly expresses the dominant trait, due to the presence of the dominant allele.

This concept is fundamental to understanding how traits pass from one generation to the next.

F2 Generation

The F2 generation emerges when individuals from the F1 generation are bred, often through self-pollination or cross-breeding among themselves. The F2 generation is key in illustrating Mendelian inheritance, as it reveals various combinations of alleles.

The offspring of this second cross present a wider variety of genetic combinations than the F1 generation. This diversity occurs because F1 offspring, being heterozygous, can pass on either one of their two alleles.

• For example, using classic Mendelian ratios, the F2 generation often displays a phenotypic ratio of 3:1 for dominant and recessive traits. This is more varied than in the F1 generation, where only the dominant trait is usually expressed.
• The F2 generation aids in identifying patterns of inheritance and providing evidence for the principle of segregation, a key aspect of Mendel's laws.

Understanding the F2 generation helps in exploring genetic variation and predicting the probability of certain traits appearing.

Homozygous Alleles

Individuals or organisms with homozygous alleles have two identical alleles for a particular gene. Homozygous can be either dominant or recessive. In genetic notation, homozygous dominant is often represented as "AA," while homozygous recessive is represented as "aa."

Homozygous alleles play a crucial role in inheritance patterns and are important in predicting the outcomes of genetic crosses. They also help in understanding why certain traits consistently appear in some offspring but not others.

• If both parents are homozygous (one dominant and one recessive), all F1 offspring will be heterozygous (e.g., "Aa").
• Among the F2 generation, the variety in combinations can lead to homozygous offspring (either "AA" or "aa"), as well as heterozygous individuals.

Recognizing homozygous alleles is essential for determining trait inheritance and is foundational for studying Mendelian genetics.