Two plants with red flowers were back crossed, which of the following results indicates that...

Explanation

This question is asking how to determine if two plants with red flowers are heterozygous, where red flowers are dominant. When two plants with red flowers are back crossed, the resulting offspring can give us information about their genetic makeup. In this case, the correct answer is Option A: 75% red and 25% white. To understand why this is the correct answer, we need to know about the principles of Mendelian genetics. In Mendelian genetics, traits are determined by genes that come in pairs, with one inherited from each parent. If the two genes are different variants (referred to as alleles), the dominant allele will determine the trait that is expressed, while the recessive allele will be masked. In the case of the red flower trait, we are told that it is dominant. This means that if a plant has at least one copy of the red flower allele, it will have red flowers. If it has two copies of the red flower allele, it will still have red flowers. When two plants with red flowers are back crossed, we can predict the possible outcomes using a Punnett square. If both plants are heterozygous (meaning they have one copy of the red flower allele and one copy of the recessive white flower allele), the Punnett square shows that there is a 25% chance of getting a homozygous recessive white flower plant, a 50% chance of getting a heterozygous red flower plant, and a 25% chance of getting a homozygous dominant red flower plant. Therefore, Option A is the correct answer because it indicates that 75% of the offspring have red flowers, which means that they are either homozygous dominant or heterozygous. The remaining 25% have white flowers, which means that they are homozygous recessive. In summary, when two plants with red flowers are back crossed, the proportion of offspring with red flowers can indicate whether the plants are heterozygous or homozygous dominant. Option A is the correct answer because it indicates that 75% of the offspring have red flowers, which means that they are either homozygous dominant or heterozygous.