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| Is red-green color blindness in
humans an inherited trait like tongue rolling? |
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Teacher Directions |
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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? |
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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? |
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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? |
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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.
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5. Does the data from the Human
Genetics project support your hypothesis?
How about some of the
archived data? |
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