INHERITING A GENE ALBINISM This is an albino skunk. The cells are not able to produce the protein that causes color. Cells in the skin produce a blackbrown pigment called melanin. The chemical melanin is produced by specialized cells in the epidermis called melanocytes. The melanin leaves the melanocytes and enters other cells closer to the surface of the skin. Different shades of skin colors is determined by the amount of melanin deposited in these epidermal cells Sunlight causes melanocytes to increase production of melanin. A tan fades because the cells break down the melanin. Some organisms, such as the octopus, can rapidly change from light to dark. They control the color by scattering the melanin in the cell for a dark color, and concentrating the melanin in the center for light color. Melanin is made by the melanocytes by chemically changing the amino acid, phenylalanin, into tyrosine and then into melanin. An enzyme is required to change tyrosine into melanin. If the enzyme is not present, then melanin cannot be produced by the melanocytes. The result of no melanin is an albino. The eyes of an albino appear pink because there is no dark melanin in the eye to absorb light. The blood in the retina and iris reflects red light, resulting in pink The gene that produces this enzyme is on chromosome 9 If both the genes produce the enzyme tyrosinase, there is plenty to convert tyrosine to melanin. If neither gene produces tryosinase, no melanin is produced and… The crow is an albino rather than the normal black What if one gene is normal and one gene does not produce the enzyme? The one normal gene produces enough enzyme to make normal crow color This albino squirrel received one albino gene from the father and one albino gene from the mother. But what if a squirrel gets a normal gene from one parent and an albino gene from the other parent? The one functioning gene produces enough enzyme to make melanin for normal coloration. Is it possible for two normal colored cockatiels to have an albino offspring? Yes! Remember the albino has two genes for albinism. One gene from the father and one gene from the mother. To be albino, both genes must be albino genes A normal colored bird could have one albino gene and one normal gene. If the sperm of a normal colored male pigeon has an albino gene and the ova it fertilizes has an albino gene than the offspring will be albino. The same happens in humans. A normal pigment father and mother can have an albino offspring. We can see this in a genetic “family tree” called a pedigree. The circles are females, the squares are males. The open symbols are normal coloration, the black symbols are albino. The parents in the circle have normal pigment. Most of the offspring received at least one normal gene from a parent. But one female offspring received an albino gene from both the mother and the father. A Punnett square is a matrix to show the genetics of a mating. What is the probability of an albino doe giving birth to a “normal” fawn if she has mated with a “normal” male? The female must have two albino genes (use small “a” for the albino gene - aa Since the albino gene is relatively rare, the male probably has two normal genes of color. (Capital “A” stands for the normal gene) - AA AA X aa Next, add the possible sperm and ova genes. A A a Aa Aa a Aa Aa As long as there is one normal gene, none of the offsprings will be albino A A a Aa Aa a Aa Aa Therefore, all offsprings will have a normal and an albino gene. A A a Aa Aa a Aa Aa An albino must get one albino gene from the father and one albino gene from the mother. Then how could an albino female penguin have an albino chick. The “normal” colored father must have one “normal coloration gene and one albino gene. There is only one way for two normal colored parents to produce an albino offspring. Both parents must have one normal gene and one albino gene. Both parents have one gene for normal and one gene for albinism. Aa X Aa The father’s sperm is 50% with normal gene and 50% with albino gene. Aa X Aa A a 50% of the mother’s ova have a normal gene and 50% of the ova have the albino gene Aa X Aa A a A a The ova and sperm may combine to form an offspring with two normal genes, a normal gene and an albino gene, or two albino genes. Aa X Aa A a A AA Aa a Aa aa Only the offspring with two albino genes will lack pigment. Aa X Aa A a A AA Aa a Aa aa Sometimes an albino is born and there is no history of albinism in the colony. The color gene in the cell that produced this white flower changed to an albino gene. A change in a gene is called a mutation.