Thus far, we have looked at the concept of dominance and recessiveness, whereby these conditions arise upon crossing two pure-breeding lines to create hybrids, and the hybrids are identical in phenotype to one parent for the particular trait in question. One of the first concepts we need to understand, is that dominance is not always complete. We are extending Mendel’s Laws in order to provide explanations for the behaviour of such traits, and not necessarily challenging them. These examples of the behaviour of certain traits implies a more complex array of interactions are at play, as these do not generate the typical Mendelian phenotypic ratios. Figure 6.5.1 Colour, Shape, and Size of Tomatoes are Examples of Multifactorial Traits In some instances, traits seem to be determined by more than one gene (multifactorial), and the environment also seemed to play a role through interaction with genes, to produce varying phenotypes. In such cases, there were no definite recessive or dominant traits observed, or more than two alleles identified in a particular cross. As more scientists began analyzing genetic crosses using different types of plants and animals, it was found that while some traits obeyed Mendel’s laws (they were determined by a single gene with 1 dominant and 1 recessive allele), many other traits did not. Complete Linkageĩ.6 Experimental Determination of Recombination FrequencyĬhapter 10 - Sex Chromosomes & Sex Linkageġ0.3 Pseudo-Autosomal Regions on the X and Y Chromosomesġ0.4 Sex Linkage: An Exception to Mendel's First LawĬhapter 11 - Recombination Mapping of Gene LociĬhapter 12 - Physical Mapping of Chromosomes and GenomesĬhapter 13 - Genes and COVID-19 Susceptibility in Humansġ3.3 Genes Implicated in Severe COVID-19 Infection in Humansġ3.4 Approaches for Vaccine Development Against SARS‐Cov‐2Īppendix A: Key Milestones in Genetics and Molecular Biology TimelineĪs we discussed in the previous section on polygenic traits, in humans most characteristics do not fit into two different phenotypes - complex traits, e.g., height, hair texture, skin colour etc., seemingly do not follow Mendelian analysis. Inheriting Parental and Recombinant Gametesĩ.4 Coupling and Repulsion (cis and trans) Configurationĩ.5 Unlinked Genes vs.Inter- and Intrachromosomal Recombination.
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