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Ch. 25 - Quantitative Genetics and Multifactorial Traits
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All textbooksKlug 12th EditionCh. 25 - Quantitative Genetics and Multifactorial TraitsProblem 24

Chapter 24, Problem 24

In a series of crosses between two true-breeding strains of peaches, the F₁ generation was uniform, producing 30-g peaches. The F₂ fruit mass ranges from 38 to 22 g at intervals of 2 g. Using these data, determine the number of polygenic loci involved in the inheritance of peach mass.

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Hi everyone, welcome back, let's look at our next question. It says quantitative trait locus mapping or Q. T. L. Is a method to determine the location of, Well when we look at our question here it says we're mapping quantitative trait locus. So when we look at our answer choices we see the choice B. Is genes responsible for quantitative traits. So that leads us pretty clearly to Choice B. Which is our correct answer. It's a way of looking for those genes that are responsible for quantitative traits such as height. And wait. I'm just gonna put up a little sort of description here and cute tail mapping. First you start with finding genetic markers associated with that trait. So looking for specific gene sequences that are associated with variation in that particular trait of interest. And then you use statistical techniques to determine if certain chromosomal areas include gene a gene or genes that influence that trait. It takes a lot of going through data because you have all this bell curve variation in those traits. So that's what Q Tl gene mapping is. Let's look through our other answer choices to understand why they are not the correct answer choice A as genes responsible for qualitative traits. So again, this name here, quantitative traits specifically points us to describing exactly what it does. So they are not it's not a search for genes responsible for qualitative traits like hair color or eye color or something like that. Choice C is mutations responsible for Mandelli in diseases um And alien diseases would be diseases inherited along dandelion inheritance patterns. So dominant and recessive things like cystic fibrosis. Um So this is not looking for those types of jeans. Again, it's during the statistical analysis to try and talk down genes associated with qualitative, excuse me, associated with quantitative traits. So choice C. Is not correct. Choice D. Is repetitive DNA sequences in the genome. Um There are methods we used to look for repetitive DNA sequences, which can point us in the direction of certain things, but this is not one of them. Uh We're looking specifically for genes that help determine quantitative traits, not particularly repetitive DNA sequences, which can be all different things. So again, we're looking when we do quantitative trait locus mapping or cute tail mapping, that's a method to determine the location of choice B genes responsible for quantitative traits. See you in the next video.
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Textbook Question

A 3-inch plant was crossed with a 15-inch plant, and all F₁ plants were 9 inches. The F₂ plants exhibited a 'normal distribution,' with heights of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and 15 inches.

What will be the outcome if the F₁ plants are testcrossed with plants that are homozygous for all nonadditive alleles?

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Textbook Question

In a cross between a strain of large guinea pigs and a strain of small guinea pigs, the F₁ are phenotypically uniform, with an average size about intermediate between that of the two parental strains. Among 1014 F₂ individuals, 3 are about the same size as the small parental strain and 5 are about the same size as the large parental strain. How many gene pairs are involved in the inheritance of size in these strains of guinea pigs?

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Textbook Question

Type A1B brachydactyly (short middle phalanges) is a genetically determined trait that maps to the short arm of chromosome 5 in humans. If you classify individuals as either having or not having brachydactyly, the trait appears to follow a single-locus, incompletely dominant pattern of inheritance. However, if one examines the fingers and toes of affected individuals, one sees a range of expression from extremely short to only slightly short. What might cause such variation in the expression of brachydactyly?

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Textbook Question

In a series of crosses between two true-breeding strains of peaches, the F₁ generation was uniform, producing 30-g peaches. The F₂ fruit mass ranges from 38 to 22 g at intervals of 2 g. Using gene symbols of your choice, give the genotypes of the parents and the F₂.

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Textbook Question

Students in a genetics laboratory began an experiment in an attempt to increase heat tolerance in two strains of Drosophila melanogaster. One strain was trapped from the wild six weeks before the experiment was to begin; the other was obtained from a Drosophila repository at a university laboratory. In which strain would you expect to see the most rapid and extensive response to heat-tolerance selection, and why?

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Textbook Question

Consider a true-breeding plant, AABBCC, crossed with another true-breeding plant, aabbcc, whose resulting offspring are AaBbCc. If you cross the F₁ generation, and independent assortment is operational, the expected fraction of offspring in each phenotypic class is given by the expression N!/M!(N−M)! where N is the total number of alleles (six in this example) and M is the number of uppercase alleles. In a cross of AaBbCc×AaBbCc, what proportion of the offspring would be expected to contain two uppercase alleles?

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