The question asks for the phenotypic ratio of a typical Mendelian dihybrid cross in the F2 generation. This requires understanding Mendel's laws of inheritance, specifically the law of independent assortment, which applies to the inheritance of two different traits simultaneously.
A) 9 : 3 : 3 : 1 is the characteristic phenotypic ratio for a Mendelian dihybrid cross in the F2 generation, resulting from the independent assortment of two pairs of alleles.
The question asks about the definition and purpose of a test cross in genetics. A test cross is a genetic cross used to determine the genotype of an individual showing a dominant phenotype. This is achieved by crossing the individual with a specific type of organism.
B) Homozygous recessive individual — Crossing an organism with a dominant phenotype with a homozygous recessive individual (e.g., aa) allows us to determine if the dominant organism is homozygous dominant (AA) or heterozygous (Aa). This is because the homozygous recessive parent will only contribute recessive alleles, thus allowing any recessive allele from the unknown parent to be expressed in the offspring.
This question is about understanding the concept of a test cross in genetics. A test cross is used to determine the genotype of an individual showing a dominant phenotype. It involves crossing the individual in question with a homozygous recessive individual. The ratio of offspring phenotypes reveals the genotype of the unknown parent.
Understand the purpose of a test cross: A test cross is performed to determine if an individual exhibiting a dominant phenotype is homozygous dominant (e.g., AA) or heterozygous (e.g., Aa).
Identify the known parent in a test cross: In a test cross, the individual with the unknown genotype (dominant phenotype) is crossed with a homozygous recessive individual (e.g., aa). The homozygous recessive individual will always produce only recessive gametes (a).
Analyze the possible outcomes if the unknown parent is homozygous dominant (AA): If the unknown parent is AA, the cross would be \(AA \times aa\). All offspring would be Aa, exhibiting the dominant phenotype. The phenotypic ratio would be 1 (dominant) : 0 (recessive).
Analyze the possible outcomes if the unknown parent is heterozygous (Aa): If the unknown parent is Aa, the cross would be \(Aa \times aa\). The offspring would be 50% Aa (dominant phenotype) and 50% aa (recessive phenotype). This results in a 1:1 ratio of dominant to recessive phenotypes.
Compare with the given information: The question states that the test cross produces offspring in a 1:1 ratio of dominant to recessive phenotype. Based on our analysis in step 4, this outcome is only possible if the parent in question (the one with the dominant phenotype) is heterozygous.
C) Heterozygous — As explained in the step-by-step analysis, a 1:1 phenotypic ratio in a test cross (crossing an individual with dominant phenotype with a homozygous recessive individual) is characteristic of the dominant-phenotype parent being heterozygous.
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 various laws proposed by Gregor Mendel.
Correct Option: B) Law of Purity of Gametes
Mendel's Law of Segregation states that during gamete formation, the two alleles for a given gene separate from each other, so that each gamete receives only one allele. This means that each gamete is 'pure' with respect to the allele it carries, hence the alternative name, Law of Purity of Gametes.
Mendel's Law of Independent Assortment describes how different genes independently separate from one another when reproductive cells develop. To observe this independent assortment, one needs to study the inheritance of at least two different traits simultaneously. This requires a specific type of genetic cross.
Correct Option: D) Dihybrid cross is the type of cross from which Mendel's Law of Independent Assortment is derived because it involves tracking the inheritance of two different traits simultaneously, allowing for the observation of their independent segregation.
The question asks to identify the Mendelian law that is considered "without exceptions". We need to recall the principles of Mendelian inheritance and understand the conditions under which each law holds true or might have exceptions.
Correct Option: C) The Law of Segregation states that during gamete formation, the two alleles for a heritable character separate from each other so that each gamete carries only one allele. This fundamental principle of meiosis is universally true for all sexually reproducing organisms and has no known biological exceptions.