o Lets say that gene C has an allele that produces an enzyme C that does not

O lets say that gene c has an allele that produces an

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o Let's say that gene C has an allele that produces an enzyme C' that does not convert C to the pigment. o If 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. o The individual will be albino. o Notice that one gene has affected several traits. o Notice 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 Genes o Parental imprinting of genes is a poorly understood phenomenon that is seen in a few cases. o This occurs when the expression of the gene seems to depend on which parent passed on the gene to the offspring . o An example is one gene that causes two different syndromes. o Prader-Willi syndrome , characterized by mental retardation, obesity and short stature occurs if the gene if inherited from the father. o Angelman syndrome , characterized by spontaneous laughter and jerky movements occurs when the same gene is inherited from the mother. o The mechanism for parental imprinting is unknown. XX. Environmental Effects on Phenotype o The environment can have real effects on phenotype, despite genotype! o Environment can alter phenotype - the appearance of an organism. o An example in the adult phase of an organism can be seen in Siamese cats , shown here. o Siamese cats have a very distinctive appearance. o In these animals, the ears, paws, tail, and nose are darker than the torso. o This 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. o XX. Environmental Effects on Phenotype
o Environmental effects on phenotype can also be seen during growth and development. o In 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. o In 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. Summary o In summary, genetics is the passing of hereditary information from generation to generation . o This can occur by asexual or sexual means . o Asexual reproduction results in all of the parent's genetic information passing on the offspring. o With sexual reproduction , half of information is derived from each parent. o Inheritance occurs via set patterns with randomness involved due to the process of meiosis. o The result is variety within a population, which is the basis for long-term stability of a population facing an uncertain and changing environment.

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