Name___________________________________________________________________________________ Bio B
Intro to Evolution:
How does genetics spur evolution?
Part One: Genetics Recap and Punnett Squares
Physical traits are observable characteristics determined by specific segments of DNA called genes. Multiple genes
are grouped together to form chromosomes, which reside in the nucleus of the cell. Every cell (except eggs and
sperm) in an individual’s body contains two copies of each gene. This is due to the fact that both mother and
father contribute a copy at the time of conception. This original genetic material is copied each time a cell divides
so that all cells contain the same DNA. Genes store the information needed for the cell to assemble proteins,
which eventually yield specific physical traits. Most genes have two or more variations, called alleles. For example,
the gene for hairline shape has two alleles – widow’s peak or straight.
An individual may inherit two identical or two different alleles from their parents. When two different alleles are
present they interact in specific ways. For the traits included in this activity, the alleles interact in what is called a
dominant or a recessive manner. The traits due to dominant alleles are always observed, even when a recessive
allele is present. Traits due to recessive alleles are only observed when two recessive alleles are present. For
example, the allele for widow’s peak is dominant and the allele for straight hairline is recessive.
[teach.genetics.utah.edu]
An individual will receive one allele from the mother and one from the
father. The specific genes a person inherits is a called a genotype. The
physical characteristics due to those genes are called the phenotype. For
example, the genotype of a person could be Ww which would result in a
phenotype of having a widow’s peak. If you inherit the same alleles (ex.
ww) from both parents, the trait is homozygous. If the traits are different
(ex. Ww) then the trait is heterozygous. See the picture to the right for
more information.
Biologists can use Punnett squares to predict possible outcomes of a
particular cross or breeding experiment. Let’s practice! Being able to roll
your tongue (R) is dominant to not being able to roll your tongue (r).
1. Cross a homozygous dominant tongue roller with a heterozygous tongue roller.
2. Cross a heterozygous tongue roller with a homozygous recessive non-tongue roller.
3. Cross a homozygous dominant tongue roller with a homozygous recessive non-tongue roller.
Before moving on, complete the white board check!
Part II: Pedigree Charts
A pedigree chart is an illustration of how a trait is passed through a family from generation to generation. Circles
represent females and squares represent males. Let’s practice!
1. How many generations are represented?
2. Fill in all genotypes (F is dominant over f for having freckles). Signify who is a carrier by shading in half of
the shape.
3. If person IV -1 has a child with a heterozygous male, what would be their child's possible genotypes?
Before moving on, complete the white board check!
Part III: Traits in a Population
In our evolution unit, we will take a look at different traits in a population. It is important to understand that
different traits create genetic diversity. For instance, a population of ladybugs may have many similarities and
differences. Using the picture below, complete the chart.
Similarities
Differences
You can observe similarities and differences among humans as well. If you look around the room, people in the
class may have freckles, some can roll their tongue, and some may have a widow’s peak. However, it is important
to remember that not all traits are “you have it or you don’t” type of traits. Think about hair color… are there just
two types? No way! There are lots of shades and colors of hair. A trait that has many different phenotypes is
called a polygenic trait. Can you think of some more examples of a polygenic trait? List them below.
Before moving on, complete the white board check!
Part IV: Genes and Evolution
Genetics plays an important role in evolution. Genes get passed on from generation to generation. Our genes give
us genetic diversity, which is why you don’t look identical to anyone else in this world (unless you are an identical
twin… you’re an exception). Regardless, the genes an organism has can affect its possibility to survive and
reproduce in the wild. Let’s make sure we understand this: