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Sindt Family Pedigree Analysis: Pigmented Iris
Marcie Sindt
Concordia University
Bio-208 General Genetics
November 21, 2014
The assignment was to create a family pedigree of a specific human trait,
tracking through three generations. I chose to look at eye color which is an
autosomal trait. People with blue or grey eye colors are homozygous recessive for
the mutant allele that causes the lack of pigment on the iris. The wild type have at
least one dominant allele giving them the ability to produce the pigment on the front
layer of the iris, resulting in brown, green, or hazel eyes.
It wasn’t hard to get the information for the assignment, as my immediate
family already spans three generations. I was able to receive the data by calling a
few family members. Eye color is influenced by more than one gene so I was afraid
that some people would tell me that they had blue/green eyes and wouldn’t know
which to pick. If I would have gone to more distant relatives I’m sure I would have
ran into this issue.
My pedigree supports the inheritance patterns of an autosomal recessive
trait. My dad has blue eyes but my mom does not. Because I have blue eyes, I was
able to conclude that my mom has to be heterozygous for eye color. It was also
interesting when looking at my sister’s family. I knew my sister was heterozygous.
Her and her husband have a daughter with blue eyes, so I was able to deduce that
her husband is also heterozygous for eye color.
I was able to eliminate the possibility of the pigmented iris gene being sexlinked dominant because if my father were affected, then both my sister and I would
have blue eyes, when she does not. I knew it could not be autosomal dominant
because in that case, an affected offspring always has an affected parent. In the third
generation you see my niece with blue eyes, who has parents who are unaffected.
I think the most interesting part of the project was being able to make
conclusions on whether a family member was a carrier for the specific gene or not. I
will be interested to find out what the eye color of my brother and his wife’s kids
will be whenever they start having a family. I once heard that blue-eyed people will
once become extinct because they will keep mating with people who are not blue
eyed and have children with the dominant allele. There may be less phenotypic
expression of the blue eyes, but that doesn’t mean that the recessive allele doesn’t
get passed on. I think you can draw that very conclusion from my pedigree. The
blue eyed trait may become less likely to be expressed, but it won’t become less
likely to be passed on to the next generation.