Suppose the mature height of a plant is a multifactorial trait un...

Question

Suppose the mature height of a plant is a multifactorial trait under the control of five independently assorting genes, designated A, B, C, D, and E, and five environmental factors. There are two alleles of each gene (A₁, A₂, etc.). Each allele with a subscript 1 (i.e., A₁) contributes 5 cm to potential plant height, and each allele with a 2 subscript (i.e., A₂, etc.) contributes 10 cm to potential plant height. In other words, a genotype containing only 1 alleles (A₁A₁B₁B₁C₁C₁D₁D₁E₁E₁) would have a potential height of [(10)(5)]=50 cm, and a genotype with only 2 alleles (A₂A₂B₂B₂C₂C₂D₂D₂E₂E₂) would have a potential height of [(10)(10)]=100 cm.
The five environmental factors are (1) amount of water, (2) amount of sunlight, (3) soil drainage, (4) nutrient content of soil, and (5) temperature. Each environmental factor can vary from optimal to poor. If all factors are optimal, assume that full potential height is attained. However, if one or more of the environmental factors is less than optimal, then height is reduced. The state of each environmental factor has an effect on growth. In this exercise, we'll assume that the growth is affected according to the following scale:

Environmental Factor State          Height Lost
Optimal (O)                                       0 cm
Good (G)                                           4 cm
Fair (F)                                              8 cm
Marginal (M)                                    12 cm
Poor (P)                                           16 cm

Thus, for example, if one environmental factor is optimal, two are good, one is fair, and one is marginal, the loss of potential height is . If the loss of height potential is greater than the height potential of the plant, the plant does not survive.

How many 1 and 2 alleles must be present to give a height potential of 80 cm?

Accepted Answer

Hi, everyone. Let's look at our next problem. It says suppose flower color in a certain plant species is controlled by three independently assorting genes designated RG and B. Each gene has two alleles and the dominant allele produces a pigment that contributes to the final flower color. The possible alleys and their effects on flower color are as follows. Now, the following is really long description of all the different alleles and colors and color combinations. So rather than read it out, word for word, I'm just going to summarize it we have in each case, the dominant alley produces the pigment in the color that corresponds to the letter. So R for red, G, for green, B, for blue. And in each case, the recessive allele of those respective genes, the result is no pigment produced and then the flower color is determined by the combination of these pigments. So red and green together gives a yellow flower, blue and green, gives a cyan flower, red and blue, gives them magenta flower. Then finally, if a flower has all three pigments, it appears white. If a flower has all recessive alleys, then the color of the flower is black. Then our problem says, identify the genotypes that will produce a white flower. And our answer choices are a heterozygous for all three genes. B, homozygous dominant for all three genes, C, both A and B or D heterozygous, four genes R and G homozygous recessive for gene B. Well, we know that a white flower is produced when all three pigments are produced in the flower. And we know that the pigments are produced by the dominant allele. So, pigments are produced by the dominant all. Well, what does this mean for the genotype? It means that you only need one copy of the dominant alley to produce the pigment color. So for all three pigments to be produced, only one dominant ally is needed per gene for those three genes. So in that case are two possibilities for a white flower. Our choice, a heterozygous for all three genes because that means there's one dominant copy of each gene and choice B. Homozygous dominant for all three genes. So our answer will be choice C which is both A and B since those are both correct, when we look at choice D, it's homozygous recessive for, for the B gene. So there will be no blue pigment produced only red and green, which we know from our answer. Choice makes the flower appear yellow in color, not white. So choice D is not our correct answer. And again, our answer here for the genotype that will produce A white flower is Choice C both A and B. See you in the next video.

Key Concepts

Multifactorial Traits

Allelic Contribution to Phenotype

Environmental Impact on Growth

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