Genotypes and Phenotypes in the World Today
No person on this planet has the exact same genotype as any other person. Even identical twins have at least a few
differences in their genotypes. As a result, no two people have the exact same overall phenotypes either. Two people
may have certain phenotypes that are the same, for instance two people may both have brown eyes, but not every part
of their phenotype will be identical. It is due to these small differences in genotypes that all humans have mostly the
same characteristics, but everyone with their own slight differences.
Think about the differences between brothers and sisters or parents and their children. All of these people have similar
DNA, or genotypes. In fact, children receive half of their genotype from their father and the other half from their
mother. However, despite the similarities in their genotypes, the phenotypes of brothers, sisters and parents are almost
always different. This must mean that small differences in genotype can lead to large differences in phenotype.
Small differences in genotype leading to large differences in phenotype are extremely obvious in cases of genetic
disorders. For instance, Tay-Sachs disease causes severe mental illness and people with the disease are unable to move
normally. Tay-Sachs is caused by an error with one gene. This one gene causes certain nerves to grow properly, but an
incorrect gene can cause these nerves to develop incorrectly. The human genotype has over 23,000 genes, and an error
in 1 of them can cause a deadly disease such as Tay-Sachs!
As scientists have become more familiar with the ideas of genotype and phenotype they have started to create ways to
look at peoples genotypes. It is now possible for a scientist or doctor to look at the DNA of a child and determine if a
person is their mother or father. It is also possible for doctors and scientists to examine the DNA of a newborn child and
look for any possible genetic disorders. Whenever a baby is born they are immediately checked for Down syndrome,
spina bifida, Tay-Sachs, sickle cell anemia, cystic fibrosis and numerous other genetic disorders. It is because of
scientists’ new understandings of genotypes and phenotypes that this new technology is available.
9
Genotypes and Phenotypes in the World Today
No person on this planet has the same genotype (DNA) as anyone else. Even identical twins have a little difference in
their genotype. Because we all have different genotypes, we also have different phenotypes (physical traits). Two people
may have certain phenotypes that are the same, for instance two people may both have brown eyes. However, not
every part of their phenotype will be identical. Two people might have brown eyes, but maybe they have different
heights. These small differences in genotypes mean that all humans have many things in common, but no one is exactly
the same as someone else.
All brothers and sisters or parents and children have similar DNA, or genotypes. This is because all children get half of
their DNA from their father and the other half from their mother. However, even though their genotypes are similar, the
phenotypes of brothers, sisters and parents are almost always different. This must mean that small differences in
genotype can cause large differences in phenotype.
The human genotype has over 23,000 genes. Small differences in this genotype can lead to large differences in
phenotype. This is easily seen in genetic disorders. For example, Tay-Sachs disease causes mental illness and people with
the disease are unable to move normally. Tay-Sachs is caused by an error with one gene (a small section of DNA). This
one gene causes nerves to grow, but an incorrect gene can cause these nerves to grow incorrectly. An error in 1 out of
23,000 genes can cause a deadly disease such as Tay-Sachs!
Today scientists know a lot more about genotypes and phenotypes. It is now possible for a scientist or doctor to look at
the DNA of a child and determine if a person is their mother or father. It is also possible for doctors and scientists to look
at the DNA of a newborn child and look for genetic disorders. Whenever a baby is born they are checked for Down
syndrome, spina bifida, Tay-Sachs, sickle cell anemia, cystic fibrosis and other genetic disorders. Because scientists and
doctors understand how genotypes and phenotypes work they can check us for problems.
7-8
Genotypes and Phenotypes in the World Today
Every person is different. We all have different DNA. Our DNA is also known as our genotype, so we all have a different
genotype. It is difficult to look at a person’s genotype because DNA is so small. Everyone also looks different. Physical
characteristics, or how we look, is called our phenotype. No one has the exact same phenotype as someone else. Part of
your phenotype, like your eye color, might be the same as another person. But you also have parts of your phenotype
that are different from that person, like maybe your height.
Brothers and sisters have similar DNA, or genotypes. Parents and children also have similar genotypes. This is because all
children get half of their DNA from their father and the other half from their mother. Even though the genotypes of
brothers and sisters are almost the same, the phenotypes of brothers, sisters are different. This must mean that small
differences in genotype (DNA) can cause large differences in phenotype (how a person looks).
Humans have over 23,000 pieces of DNA called genes. All of these genes and DNA are called our genotype. Small
differences in this genotype can cause large differences in phenotype. Differences in DNA can be seen in genetic
diseases. For example, Tay-Sachs disease causes mental illness. Tay-Sachs is caused by an error in one gene. This one
gene causes nerves to grow. If a person has a mistake in this gene then their nerves grow incorrectly. One bad gene out
of 23,000 can cause a terrible disease!
Today scientists know a lot more about genotypes and phenotypes. It is now possible for a scientist or doctor to look at
the DNA of a child. If a doctor looks at this genotype they know who is their mother or father. It is also possible for
doctors and scientists to look at the DNA of a newborn child and look for genetic disorders. Whenever a baby is born
they are checked many diseases like Down Syndrome. Because scientists and doctors understand how genotypes and
phenotypes work they can check us for problems.
6