Height in humans is very strongly genetically controlled, but there are many, many different genes that control height. And this is why people are not the exact height of their parents.
Skin color is another trait that is very obvious in humans that is controlled by many, many different genes. And this is why you get differences between parents and children in skin color, although they tend to resemble one another. Pleiotropy Some genes affect more than one phenotypic trait. Epistasis Some genes affect the expression of other genes. The sample on the left is mixed with anti-B antibodies; the sample on the right is mixed with anti-A antibodies.
Agglutination by the anti-A antibodies on the right shows that the sample is type A blood. Review What is non-Mendelian inheritance? Explain why the human ABO blood group is an example of a multiple allele trait with codominance. What is incomplete dominance? Give an example of this type of non-Mendelian inheritance in humans. Explain the genetic basis of human skin color. How may the human trait of adult height be influenced by the environment?
Define pleiotropy, and give a human example. What is the difference between pleiotropy and epistasis? Which of the following terms best matches each trait description? Choose only the one term that best fits each trait. A trait where each allele of a heterozygote makes an equal contribution to the phenotype. A trait controlled by a single gene that has three different versions. A trait controlled by a single gene where one allele is fully dominant to the only other allele. People with type O blood cannot receive a blood transfusion from anyone besides others with type O blood.
True or False. People with type O blood can be heterozygous for this trait. To learn more about non-Mendelian Inheritance, check out this video:.
Attributions Family by Henry M. Anti-A and Anti-B. A antigen. B antigens. A and B antigens. The genetic variability is stored in the form of polygenic complexes. Segregation and recombination of polygenic genes after interbreeding results in the release of hidden variability in a species. Humans are diploid creatures. This means that for every chromosome in the body, there is another one to match it.
However, there are organisms that have more than two sets of chromosomes. The condition is called polyploidy. Know more about this topic through this tutorial Read More. Genes are expressed through the process of protein synthesis. This elaborate tutorial provides an in-depth review of the different steps of the biological production of protein starting from the gene up to the process of secretion. Also included are topics on DNA replication during interphase of the cell cycle, DNA mutation and repair mechanisms, gene pool, modification, and diseases Skip to content Main Navigation Search.
Dictionary Articles Tutorials Biology Forum. Table of Contents. Biology definition: Polygenic inheritance is a non-Mendelian pattern of inheritance in which a particular trait is produced by the interaction of genes at many loci i. Compare: monogenic inheritance.
Related term: polygene. Polygenic inheritance is also involved in quantitative traits , in which multiple gene loci each contribute in a similar way to the phenotype so that the total number of contributing alleles determines the phenotype. In humans, height, weight, and skin color are examples of quantitative traits. For instance, the height of an adult human is determined by not just a single gene but by more than genes apart from the other non-genetic factors such as environment and nutrition.
In quantitative traits, the Mendelian ratios are replaced by a normal distribution curve, with the two ends of the curve defined by the two extremes possible for the phenotype.
The trait is a result of the cumulative effects of many genes Mendelian inheritance. Polygenic inheritance. Monogenic inheritance.
Alleles that contribute to continuous variation Allelic pair. Contributing alleles. Non-contributing alleles. Genes producing a phenotype when expressed together Genome. Which of the following shows polygenic inheritance? Free earlobes as a dominant trait vs. Pink flower color trait as a result of a cross between white-flowering and red-flowering plants. For instance, a recent study found over genes linked to variation in height [1]. When there are large numbers of genes involved, it becomes hard to distinguish the effect of each individual gene, and even harder to see that gene variants alleles are inherited according to Mendelian rules.
Instead, they vary in small gradations, forming a spectrum or continuum of possible phenotypes. However, we can use an example involving the color of wheat kernels to see how Mendelian inheritance of multiple genes plus a little incomplete dominance of alleles can produce a broad spectrum of phenotypes [3].
Each comes in two alleles, one of which makes a unit of pigment the capital-letter allele and one of which does not make any pigment the lowercase allele. Thus, the aa genotype would contribute zero units of pigment, the Aa genotype would contribute one unit, and the AA genotype would contribute two—basically, a form of incomplete dominance. Each of the parent plants would have three units of pigment, or pinkish kernels.
Their offspring, however, could display seven different categories of phenotypes, ranging from zero units of pigment aabbcc and pure white kernels to six units of pigment AABBCC and dark red kernels, with the intermediate phenotypes being most common. This example illustrates how we can get a spectrum of slightly different phenotypes something approaching continuous variation with just three genes whose alleles display incomplete dominance.
0コメント