The pedigree chart above shows the incidence of color-blindness in a seleceted family. Color-blindness is a sex-linked diseases (the gene for the color-blind trait is located on the 'X' chromosome). Genotypes and phenotypes involved with this trait are as follows:

XY   Normal color vision male
X^Y   Color blind male
XX   Normal color vision female
XX^   Normal color vision female, carrier for color-blindness
X^X^   Color blind female

1. Do you think that color-blindness is a dominant or recessive gene disease? What evidence leads you to this hypothesis?

2. Identify the color blind individuals in the pedigree. What sex are the color-blind individuals?

3. Would you expect a color blind phenotype to show up more often in males or females of a population? Explain.

4. If Lori, in the above pedigree, were to marry a color blind man, what would the probability be of having a color blind son? A color blind daughter?

5. Could a man with normal color vision have a son that is color blind? Explain. A daughter that is color blind? Explain.


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