Is red-green color blindness in humans an inherited trait?
This investigation is designed so that students can answer these questions:
- Is red-grenn colorblindness an inherited trait?
- How is red-green colorblindeness inherited?
Color blindness is an inherited trait that can be passed on through reproduction but it has some peculiarities. It is recessive and not very prevalent in the gene pool. Because of this, color blindness does not appear very often in the population. In addition, it is a sex-linked gene on the X chromosome. Thus males only have one gene to express color vision. If it happens to be the recessive allele, then males are color blind. Females, on the other hand, must have both alleles recessive in order to be color blind. Does the data collected at the Human Genetics project exhibit these characteristics?
In order to continue, you need to download or view the data submitted about the individuals who have indicated that they are red-green color blind. Have students form groups of 2 or 3 students and discuss the following questions which you can download. Afterwards students can present answers or they can write up a short report.
1. Is color blindness dominant or recessive?
Using pedigree analysis, determine whether or not color blindness is dominant or recessive. Think about this, if a person is color blind and color blindness is dominant, then which or what parents would have to be color blind?
2. Does Mendel's Laws apply to its inheritance?
IF red-green color blindness is an inherited trait, THEN at least one parent or grandparent must have been a carrier of a color blind allele if it is recessive and one parent must express the phenotype color blind if it is dominant. Does that mean one of them had to be color blind? Can you find any evidence in a person's genetic history that supports inheritance?
3. Anything odd about the inheritance of color blindness? Investigating further, IF red-green color blindness is controlled by a gene on a normal body (X)chromosome, THEN the number of color blind males will equal the number of color blind females. (Remember males have one X and one Y chromosome while females have two X chromosomes. The Y chromosome is shorter than the X chromosome and thus is missing some genes. Males then have some characteristics that are expressed by one sex linked gene instead of two.) What percentage of students showing color blindness are male? What percentage of students showing color blindness are female?
4. Now let's assume that red-green color blindness is controlled by a dominant gene on the sex linked X chromosome. Write a prediction for the percentage of female children that would be born to these parents: mother is not color blind; father is color blind.
5. Does the data from the Human Genetics project support your hypothesis? How about some of the archived data?