Name: Leah P_______________
Date: January 3, 201
Genetics and Inheritance
What is a gene?
A gene is a basic unit of inheritance in living things. The branch of science that studies genes
is called genetics. In humans, genetics determine many of our characteristics such as eye color,
hair color and even your height. From the moment that a person is an embryo to the moment
they pass away, the genes are constantly at work. Although genes determine a major part of
each characteristic, some are also influenced by environmental conditions such as nutrition and
health.
Genes are made up of chemicals called deoxyribonucleic acids (DNA). There are four
different DNA building blocks. Multiple genes are found on chromosomes that also contain
various regulation elements for genes. A single chromosome can contain many genes and can
have more than 200 million DNA building blocks. In some organisms, including humans, DNA is
found in a double helix format. In general, where genes are going to be passed on to the
offspring, the genetic information is duplicated by a process called DNA replication where
various molecules copy the original DNA and make a new one just like to original.
Genetic inheritance
One of the earliest studies in genetics was conducted by Mendel. He was looking at pea plants
trying to determine why some of them had white flowers whereas others had purple ones. He
crossed plants with different flower colors and same flower colors to see what the color of the
resulting baby plants’ flowers were. By doing this, he discovered the concept of alleles; these
are different variations of the same gene.
In the case of pea plants, there are two alleles that determine the color of the pea plants; purple
allele (P) and the white allele (p). An interesting fact about these alleles is that the purple gene
version is dominant and the white version recessive. Let’s say that a pea plant has in its genes
a purple allele from its mom and a white allele from its dad, in this case, the purple will dominate
and the flower of the baby plant will be purple. The genetic makeup of the plant, presence of
purple (P) allele and the white allele (p) is referred to as the genotype. The resulting physical
characteristic, in this case the flower color, is called the phenotype. Below is a summary of the
pea plant flowers’ colors based on different genotypes:
Genotype Phenotype
Pp Purple flower
PP Purple flower
pp White flower
Genetics and Inheritance (cont’d)
Usually, a Punnett square is used in determining the possibility of a baby having a certain
genotype based on the parents genotypes. Let’s say there is a mother and a father plant with
purple flowers, and we know that their genotypes are both Pp. If these have a baby plant, what
would be the genotype and the phenotype?
Maternal
p
P
PP
Pp
p
Pp
Pp
Parental
P
Looking at the Punnett square above, we see that there is a 2 out of 4 chance that the baby will
have a Pp genotype, 1 out of 4 chances that it will have a PP and 1 out of 4 chance that it will
have a pp. This means that 3 out of 4 baby flowers would have purple flowers and that there is
only a 1 out of 4 chance that there will be a white baby flower.
Genetic inheritance for many organisms and phenotypes is slightly more complicated than our
earlier example. In some cases, the alleles have co-dominance where the resulting phenotype
of the combination of the two, give a third type of new phenotype. Also, there are cases where
one trait is influenced by more than one gene; eye color and skin color are two examples of
these traits. Copyright 2007 InstructorWeb Name__________________________ Date_________________
Genetics Questions
1. What is a gene, chromosome, DNA and how do they relate to one another?
Gene – a basic unit of inheritance in living things
Chromosome – where genes are found
DNA – how genes are made of chemicals
They relate to each other because genes are in each chromosome and DNA.
2. What are some characteristics that are influenced by our genes?
Eye color, hair color, skin color.
3. Make family tree of eye colors by filling in the tree below.
ee – brown
EE – blue
Ee - blue
Grandma
ee
------------
Grandpa
EE
-------------
Grandma
EE
------------
Mom
Ee
------
Grandpa
Ee
------------
Dad
EE
-----ME
Ee
-------
4. If a father has blue eyes with a two blue eye genes, which are recessive (bb), and a mother
had brown eyes with one recessive one dominant gene (Bb), make a Punnett square and see
what the odds are for their baby having blue eyes.
Parental
Maternal
b
B
Bb
b
Bb
b
Bb
bb