Assume that fruit colour is controlled by three loci each contributing an equal amount to the trait. Which of the following plant genotypes will have the fruit colour which is most common in this population?

Question

Assume that fruit colour is controlled by three loci each contributing an equal amount to the trait.  Which of the following plant genotypes will have the fruit colour which is most common in this population?

BlackTom AI · Accepted Answer

Question restatement: The trait of fruit colour is controlled by three loci, each contributing equally to the trait. Which plant genotype will have the fruit colour that is most common in this population? Answer options: AaBbcc, AabbCc, AaBbCc, AABBcc.

Option 1: AaBbcc. Here, the plant is heterozygous at the first two loci and homozygous recessive at the third. This yields intermediate contributions from the first two loci and no contribution from the third, giving a specific additive score. In a polygenic, additive model with equal contributions per locus, many genotypes can map to similar mid-range phenotypes; however, this genotype represents two active (Aa and Bb) contributions and two inactive (cc) at the remaining, which may lead to a commonly observed intermediate pigment level.

Option 2: AabbCc. This genotype is homozygous recessive at the first locus, heterozygous at the third locus, and homozygous dominant at the second locus is not implied here; the notation shows aa at the first, Bb at the second, and Cc at the third, which mixes a recessive state in one locus and a heterozygous state in another. The resulting additive score combines low contribution from the first locus with moderate contribution from the second and third, potentially yielding a different mid-range phenotype than AaBbcc, making its frequency dependent on allele distribution and not necessarily the most common.

Option 3: AaBbCc. This genotype is heterozygous at all three loci, giving one contributing unit from each locus and an overall intermediate additive score across the entire trait. In a population where each locus contributes equally and allele frequencies are not extremely biased, the genotype with heterozygosity across all loci often corresponds to an intermediate, central phenotype, which tends to be among the most frequent phenotypic categories due to averaging effects across loci.

Option 4: AABBcc. This genotype is homozygous dominant at the first two loci and homozygous recessive at the third. It yields high contribution from the first two loci and no contribution from the third, resulting in a relatively higher additive score compared with genotypes with recessive or heterozygous states at multiple loci. Depending on allele frequencies, this combination is less likely to be the single most common mid-range phenotype when a full spectrum of combinations is possible.

Why the correct (most common) phenotype tends toward the middle: In an additive polygenic model with three loci contributing equally, the distribution of the phenotype across a population tends to be bell-shaped, centered around mid-range total contributions. The genotypes that maximize the likelihood of achieving this middle value are those that balance contributions across loci. A genotype with heterozygous states at all loci (AaBbCc) tends to produce a mid-range phenotype and, under typical equal-frequency conditions, is often among the most probable genotype configurations.

Why other options are less likely to be the most common: AaBbcc (Option 1) and AabbCc (Option 2) each fix recessive alleles at one locus or combine heterozygosity in only two loci with recessive states elsewhere, shifting the additive score away from the exact mid-point compared with AaBbCc, and thus are less likely to be the single most common phenotype under symmetric allele frequencies. AABBcc (Option 4) concentrates contributions into the first two loci with no contribution from the third, producing a higher-than-mid additive score and typically a less frequent mid-range category when the population distribution peaks near the center.

Putting it together: Under standard assumptions of three loci contributing equally to a polygenic, additive trait and with similar allele frequencies, the genotype AaBbCc often represents the mid-range, central phenotype and is commonly observed as one of the most frequent genotypes. This aligns with the provided correct answer choice in the data set, AaBbCc, though real outcomes depend on the exact allele frequencies in the population and any dominance effects that might shift the distribution.

Assume that fruit colour is controlled by three loci each contributing an equal amount to the trait. Which of the following plant genotypes will have the fruit colour which is most common in this population? 单项选择题

类似问题

Most characteristics are the result of the interaction of many different genes. This is the concept of....

What does polygenic refer to?

How are quantitative traits controlled?

Assume that fruit color is controlled by three loci each contributing an equal amount to the trait. Which of the following plant genotypes will have the fruit colour that is most common in this population?

CHOOSE THE BEST ANSWER From a biological standpoint, efforts to classify people into discrete groups based on skin color are inherently arbitrary because...

How are quantitative traits controlled?

What is TRUE about complex traits?

In the lecture videos, which of the following traits was highlighted to demonstrate polygenic traits and the resulting spectrum of variation that occurs?

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单