oLet's say that gene C has an allele that produces an enzyme C' that does not convert C to the pigment. oIf the individual is homozygous recessive for this allele, then no pigment will be produced and there will be no pigment in the eyes, skin or hair. oThe individual will be albino. oNotice that one gene has affected several traits. oNotice in the pictures of the deer that the color of the coat, the nose, ears, hoofs, and eyes are all affected.XIX. Parental Imprinting of GenesoParental imprintingof genes is a poorly understoodphenomenon that is seen in a few cases. oThis occurs when the expression of the gene seems to depend on which parent passed on the gene to the offspring. oAn example is one gene that causes two different syndromes. oPrader-Willi syndrome, characterized by mental retardation, obesity and short stature occurs if the gene if inherited from the father. oAngelman syndrome, characterized by spontaneous laughter and jerky movements occurs when the same gene is inherited from the mother. oThe mechanism for parental imprinting is unknown.XX. Environmental Effects on PhenotypeoThe environment can have real effects on phenotype, despite genotype!oEnvironment can alter phenotype - the appearance of an organism. oAn example in the adult phase of an organismcan be seen in Siamese cats, shown here. oSiamese cats have a very distinctive appearance. oIn these animals, the ears, paws, tail, and nose are darker than the torso. oThis is because the torso is warmer and the cooler temperature of the extremities alters gene expression by affecting an enzyme and leading to a darker coat color at these parts of the body.oXX. Environmental Effects on Phenotype
oEnvironmental effectson phenotype can also be seen during growth and development. oIn plants, potatoes left under a sink will develop long, colorless, stringy stems and small leaves. The same potato grown in a garden will have short, green stems with large leaves. oIn humans,protein deficiency in a child's diet can lead to kwashiorkor, with a bloated belly as a typical symptom. If allowed to proceed over the long term, kwashiorkor can lead to mental retardation.SummaryoIn summary, genetics is the passing of hereditary information from generation to generation. oThis can occur by asexual or sexual means. oAsexual reproductionresults in all of the parent's genetic information passing on the offspring. oWith sexual reproduction, half of information is derived from each parent. oInheritance occurs via set patterns with randomness involveddue to the process of meiosis. oThe result is variety within a population,which is the basis for long-term stability of a population facing an uncertain and changing environment.