The question asks for the phenotypic ratio of a typical Mendelian dihybrid cross in the F2 generation. This involves understanding Mendel's laws of inheritance, specifically the Law of Independent Assortment, when two traits are considered simultaneously.
A) 9 : 3 : 3 : 1 is the classic phenotypic ratio observed in the F2 generation of a Mendelian dihybrid cross, assuming complete dominance for both traits and independent assortment of genes.
The question asks about a test cross. A test cross is a genetic cross designed to determine the genotype of an individual showing a dominant phenotype. Since the dominant phenotype can result from either a homozygous dominant (e.g., AA) or a heterozygous (e.g., Aa) genotype, a test cross helps differentiate between these two possibilities.
B) Homozygous recessive individual — Crossing an organism with a dominant phenotype with a homozygous recessive individual allows us to determine if the dominant parent is homozygous dominant or heterozygous based on the phenotypes of the offspring. This is the definition and purpose of a test cross.
The question describes a test cross where the offspring show a 1:1 ratio of dominant to recessive phenotypes. We need to determine the genotype of the parent in question based on this outcome. A test cross involves crossing an individual with an unknown genotype (showing the dominant phenotype) with a homozygous recessive individual.
C) Heterozygous — As explained in the step-by-step analysis, a test cross involving a heterozygous individual (e.g., Aa) and a homozygous recessive individual (aa) will produce offspring with a 1:1 phenotypic ratio of dominant to recessive traits.
The question asks for an alternative name for Mendel's Law of Segregation. We need to recall the fundamental principles of Mendelian genetics and the specific characteristics of each law proposed by Mendel.
Correct Option: B) Law of Purity of Gametes — This law is an alternative name for Mendel's Law of Segregation because it emphasizes that each gamete formed during meiosis receives only one allele for each gene, making the gamete "pure" with respect to that allele. For example, if an individual has alleles 'A' and 'a', their gametes will either carry 'A' or 'a', but not both.
The question asks to identify the type of genetic cross from which Mendel's Law of Independent Assortment is derived. This law describes how different genes independently separate from one another during the formation of gametes. To observe this independent assortment, one needs to study the inheritance of at least two different traits simultaneously.
D) Dihybrid cross — Mendel's Law of Independent Assortment is derived from dihybrid crosses because it requires observing the inheritance patterns of two different traits simultaneously to see if they segregate independently.
The question asks to identify the Mendelian law that is considered "without exceptions." We need to recall the principles of Mendelian inheritance and their universality.
Correct Option: C) The Law of Segregation is considered the "law without exceptions" because the separation of alleles during gamete formation is a universal biological process in sexually reproducing organisms. Each gamete invariably receives only one allele for each gene.