A total of 20 distinct phenotypic categories should be observed for a polygenic trait in humans that results from segregation of additive alleles for 10 genes Heritability measures the extent to which environmental variation contributes to the total phenotypic variation. (VA + VD + VI)/ VP can be used to calculate broad sense heritability (H2) As broad sense heritability (H2) approaches 0.0, almost all the variation in phenotype is VG If for a specific trait monozygotic twins have a phenotypic variance of 15% and dizygotic twins have a phenotypic variance of 40%; VE for monozygotic twins is 15% and VG for dizygotic twins is 50% High concordance values for both identical and fraternal twins indicate likely strong genetic influence for a condition A low h2 value trait could most effectively be selected in an animal breed Gene-environment interactions widen the potential phenotypic range While most additive polygenic traits show continuous distribution, threshold traits can be divided into two or more categories based on their contribution to genetic liability.
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We are given that monozygotic twins have a phenotypic variance of 15% (VP_MZ = 0.15) and dizygotic twins have a phenotypic variance of 40% (VP_DZ = 0.40). Show more…
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Two alleles (A and a) at one locus produces 3 distinct phenotypes. Two alleles each at two different loci (A and a, B and b) produce 5 distinct phenotypes. Two alleles each at three loci produce 9 distinct phenotypes. (these statements assume that the alleles at any one locus are co-dominant and that each gene makes an equal contribution to the phenotype). Derive a formula to express this relationship (let n = the number of genes) Each of the most extreme phenotypes for a trait determined by two alleles at one locus are found in a proportion of ÂĽ in the F2 generation. If there are two alleles of two genes that determine a trait, each extreme phenotype will be present in 1/16 of the F2 offspring. In common wheat (Triticum aestivum), kernel color varies from red to white and the genes controlling the color act additively, that is, alleles for each gene are semidominant and each gene contributes equally to color. A true-breeding red variety is crossed to a truebreeding white variety, and then the F1s are selfed. Among the F2 offspring, 1/256 have white kernels and 1/256 have red kernels, and the remainder have intermediate colors. How many genes control kernel color in this cross?
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Polygenic trait Human skin color is a polygenic trait that is determined by the additive effects of several different genes. Over 25 genes can control skin color! A polygenic trait is one whose phenotype is influenced by more than one gene. Traits that display a continuous distribution in a population such as height or skin color, are polygenic. The inheritance of polygenic traits does not show the phenotypic ratios characteristic of Mendelian inheritance, though each of the genes contributing to the trait is inherited as described by Gregor Mendel. Many polygenic traits are also influenced by the environment and are called multifactorial. If we assume that each square in the Punnett square represents one offspring of the heterozygous AaBbCc parents, then the squares below show the possible phenotypes. AaBbCc X AaBbCc Gametes : ABC, ABc, AbC, aBC, Abc, aBc, abC and abc 1.The genotypes of 1____________________, 2____________________,3____________________ 4 ____________________, 5 ____________________, 6 ____________________ 0__aabbcc____________________ 2.Look at Fig 4, what is the genotype of the highest frequency of people in this population? 3.In a population of 64 individuals, what percentage of people have the phenotypes as designated by the numbers. 4.The number of people in the categories of 0-6 genotypes and phenotypes are 1. ____6/64____________, 2.____________________,3.____________________ 4 ____________________, 5.____________________, 6.____________________ 0. __None____________
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