Complex traits · The traits Mendel studied were single-gene traits o Each one was determined by variation at a single gene and the traits are for the most part not influenced by the environment o However, complex traits are influenced by multiple genes AND the environment o Complex traits are much more prevalent than single gene traits Now that sequencing genes is much easier, complex traits are better studied E.g. the sanger institute is where the UK's effort for sequencing genomes is located o There are also lots of centres in America that sequence genomes of model organisms, humans, etc - often looking at complex traits . Why complex traits are important o Many common human diseases are also complex traits o For example, high blood pressure, obesity, diabetes, and depression o Complex traits are influenced by multiple genes as well as by the environment o This affects crops we grow as well. E.g. grain size, shape & yield in rice is a complex trait - seen below o It also has implications for healthcare, treatments and personalised medicine o Height is a good e.g. of a complex trait (demonstrates normal distribution, which tends to be typical of complex traits) - seen below o Most single-gene traits often appear in one of two or a few different phenotypes, such as round vs. wrinkled seeds. These traits are often identified by mutagenesis o In many complex traits, the phenotype is determined by a measurement: number, size, shape, yield etc. o Complex traits like these are called quantitative traits because they are measured along a continuum with only small intervals between similar individuals o Complex traits can also be influenced by the environment a Zhenshan 97 NIL (ZS97) Zhonghua 11 H94 NIL (H94) Minghui 63 · Expression of complex traits is susceptible to lifestyle choices and other environmental factors - E.g. o Inadequate nutrition may slow growth and development. o Increased salt intake is associated with an increased likelihood of high blood pressure. A poor diet high in fat and carbohydrates is a risk factor for obesity and diabetes. o Also .... o Soil moisture and nutrients are needed for maximum yields in crops o These environmental effects are seen in true-breeding (homozygous) strains, also called inbred lines.
o Most crops are grown from the genetically identical seeds, but the variation observed throughout a field is due to the environment (i.e., sunlight, water, wind, nutrients, etc.). Explaining complex traits Understanding that Mendel's laws also apply to complex traits o Because many genes contribute to complex traits, different genotypes can have very similar phenotypes o It is difficult to see the effects of individual genes (and Mendelian ratios are not easily observed) o Where the effects of the environment are low and the number of genes is small, the basis of the trait can be analysed o It is possible to demonstrate that complex traits are subject to the same laws for single-gene traits o But that the inheritance patterns are more difficult