Alterations to Mendel. Incomplete or partial dominance Codominance Multiple alleles and Lethal alleles Gene interactions & multiple genes Epistasis and complementation Effect of environment Extranuclear inheritance Sex-linked, sex-limited, & sex-influenced
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How mosaics are made.
Events during development.
Two homologous chromosomes, blue & red.
Black indicates inactivation = Barr body
Classic example: the calico cat.
One X chromosome codes for orange fur, the other for black. Cat shows characteristic mosaic patterns caused by one or the other X chromosome being inactivated.
White fur results from the effect of another gene.
Red: active genes.
Xic is responsible for this process; if moved to an autosome, that chromosome will be inactivated.
Besides XIC, a few other genes on the chromosome remain active. Logically, they are genes also found in the pseudoautosomal region of the Y chromosome.
Including a “white” which is 1/16 of total. Closer view: 1:4:6:4:1
4+ alleles, 3+ alleles, 2+ alleles, 1+ allele, none
Variation appears continuous because these traits often affected by the environment.
note bell curve.