Height in humans depends on the additive action of genes. Assume that this trait is controlled by the four loci R, S, T, and U and that environmental effects are negligible. Instead of additive versus nonadditive alleles, assume that additive and partially additive alleles exist. Additive alleles contribute two units, and partially additive alleles contribute one unit to height.

If an individual with the minimum height specified by these genes marries an individual of intermediate or moderate height, will any of their children be taller than the tall parent? Why or why not?

Video transcript

Hi everyone, welcome back. Here's our next question, assume that the flower color of a plant depends upon the additive action of the genes. If one 64th of the F two generation flowers were either blue or white, what would be the number of poly genes involved in the flower color of the aforementioned plant? So we're talking about not, you know, plain old dominant versus recessive inheritance and those Mandell ian punnett squares, but apologetic inheritance. So instead of one being dominant over the other, we've got multiple alleles and we add together the effect of those alleles. So the way to analyze how many aliens are involved is if we know what percent of the offspring have the most extreme phenotype SIS. Now if we think that's true, we look at the F- two generation. So that's if we start with a cross of grandparents who have the most extreme phenotype sis. So in essence have um all dominant alleles, although again, we're not straight dominant or recessive, but the darkest color for instance, in this case versus all the recessive or lightest color alleles. So in this case we're saying that we're looking at either blue or white flower color. So you would have started started with grandparents, a blue flower flowered plant crossed with a white flowered plant. In this case, since we have apologetic inheritance. Looking at these are the two most extreme phenotype, we automatically know that this one has all of the most dominant alleles. So that would be our original cross and then our F1 generation would be identical. Hetero cigarettes. For all of the alleles involved. Since these parents have just a single type of gamete they can give for each value. And then our F2 generation, we'll have a bell shaped distribution of phenotype. And again if you kind of imagine when we have our Mandelli inheritance and we have our 9 to 3 to 3 to 1 ratio of a di hybrid cross. Um Instead of having distinct either or phenotype, sis dominant or recessive phenotype, you add up the effect of the different levels. And you can imagine that you'll end up with the largest number with the sort of um midway point phenotype and the smallest number at either extreme. So we know here in our F two generation, how many have the parental or in this case grand parental phenotype? And we know that that is 164th of all the offspring. And we actually have a formula for determining how many alleles are involved in this inheritance. If we know this particular ratio and that is that The number of offspring expected to have this most extreme grand parental phenotype would be 1/4 to the 9th power. Where n. Is the number of genes involved in this apologetic inheritance. So we have 164th in this case equals 1/4 to the end power. Well we know that 1/4 is one. Excuse me? We know that one 64th is one Over 4 to the 4th power. And therefore that's going to equal 1/4 to the 4th power, So N must equal four, and therefore there are four poly genes involved in determining the flower colour of this plant. And we have the answer here as choice. D. four. See you in the next video.