To determine the phenotypic ratio of a monohybrid cross between two heterozygous parents, we use a Punnett square. This allows us to visualize all possible combinations of alleles from the parents and then determine the genotypes and corresponding phenotypes of the offspring.
We set up a Punnett square with the gametes from one parent along the top and the gametes from the other parent along the side:
| A (from parent 1) | a (from parent 1) | |
|---|---|---|
| A (from parent 2) | AA | Aa |
| a (from parent 2) | Aa | aa |
So, the genotypic ratio is \(1 \text{ (AA)} : 2 \text{ (Aa)} : 1 \text{ (aa)}\).
Therefore, we have:
The phenotypic ratio is \(3 \text{ (Dominant)} : 1 \text{ (Recessive)}\).
Correct Option: B) 3:1
To determine the genotypic ratio in a monohybrid cross, we use a Punnett square. A monohybrid cross involves tracking the inheritance of a single gene, and in this case, both parents are heterozygous (Aa).
| A (from Parent 1) | a (from Parent 1) | |
|---|---|---|
| A (from Parent 2) | AA | Aa |
| a (from Parent 2) | Aa | aa |
Correct Option: A) 1:2:1 is the correct genotypic ratio for a monohybrid cross between two heterozygous individuals (Aa x Aa).
The question asks about Mendel's Law of Segregation. We need to identify the statement that accurately describes this fundamental principle of genetics.
Correct Option: D) Alleles of a gene separate during gamete formation
The question asks for the phenotypic ratio in the F2 generation of a dihybrid cross (AaBb × AaBb). This involves understanding Mendel's law of independent assortment and how to combine the phenotypic ratios of two monohybrid crosses.
C) 9:3:3:1 — This is the standard phenotypic ratio for the F2 generation of a dihybrid cross where both parents are heterozygous for both traits (AaBb x AaBb) and the traits assort independently.
The question asks about a "test cross" in genetics. A test cross is a fundamental genetic tool used to determine the genotype of an individual expressing a dominant phenotype. The key to a test cross is to mate the individual with an organism whose genotype is known and will reveal the unknown alleles.
C) A homozygous recessive individual — Crossing a dominant phenotype individual with a homozygous recessive individual is the definition and purpose of a test cross. This allows geneticists to determine if the dominant phenotype individual is homozygous dominant or heterozygous based on the phenotypes of the offspring.
The question asks to identify the type of cross used to determine if an organism exhibiting a dominant phenotype is homozygous or heterozygous. This requires understanding the purpose of different genetic crosses.
A) Test cross is the correct answer because it is the specific genetic cross used to determine whether an individual showing a dominant phenotype is homozygous dominant or heterozygous.