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Lecture 18

BIOL 151 Lecture 18: Bio 151 - Chapter 18

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BIOL 151

BIOL 151 – Chapter 18 18.1 Heredity and Environment • Complex traits are affected by the environment o Environmental Risk Factor: a characteristic in a person’s surroundings that increases the likelihood of developing a particular disease o Environmental effects are also important in agriculture ▪ The environmental effects also affect average phenotype for complex traits and also affect the variation in phenotype from one individual o the next o Environmental effects on complex traits in animals are evident in true-breeding ▪ True-breeding, homozygous strains are called Inbred Lines, and are often used for research • Complex traits are affected by multiple genes o The number of genes affected complex traits is usually so large that different genotypes can have very similar phenotypes, which also make it difficult to see the effects of individual genes on a trait o In a few traits, the effects of the environment are minor and the number of genes is small o When differences in phenotype due to the environment can be ignored, the genetic variation affecting complex traits can be detected more easily • The relative important of genes and environment can be determined by differences among individuals o It is possible to separate genes and environment in regard to their effects on the differences (variations) among individuals within a particular population ▪ For some traits, the variation is due mainly to genetic differences • Genetic and environmental effects can interact in unpredictable ways o Norm of Reaction: a genotype’s lines in which it graphically depicts how the environment affects phenotype across a range of environments o Variation in the effects of the environment on different genotypes is known as Genotype-by-Environment Interaction ▪ This is important because it implies that the effect of a genotype cannot be specified without knowing the environment, and the other way around ▪ It also implies that the interplay between genes and the environment is difficult to predict 18.2 Resemblance Among Relatives • For complex traits, offspring resemble parents but show regression toward the mean o Regression toward the Mean ▪ The offspring exhibit an average phenotype that is less different from the population mean than that of the parents • This means that when the average height of the parents is smaller than the population mean, then the average height of the offspring is greater than that of the parents BIOL 151 – Chapter 18 • It also means that when the average height of the parents is greater than the population mean, the average height of the offspring is smaller than that of the parents • Heritability is the proportion of the total variation due to genetic differences among individuals o For a complex trait, the heritability determines how closely t
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