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Reviewing Genotypes and Phenotypes
In the following class work activity, we are reviewing genotype and phenotype. We use the word genotype to
describe the genes/alleles an organism has inherited from its parents.
Genotypes are illustrated by using TWO letters for each allele (one from each parent.) An allele is one of two or
more versions of a gene. (Ex: X and x are two alleles for a gene. XX, Xx, and xx are genotypes)
Phenotypes refer to how an organism looks (physical traits) based on the genotype. Answer the following
questions filling in genotype or phenotype as necessary. An individual inherits two alleles for each gene, one from
each parent.
Below are the different alleles for 5 traits. (Capital = dominant, lowercase = recessive). Complete the data table
using this information.
A=right handed
B=brown
C=curly
D=detached ear lobe
E=Freckles
a=left handed
b= blue
c=straight
d=attached ear lobe
e=no freckles
Genotype
Phenotype
Genotype
Aa
Bbcc
BB
eebbcc
Phenotype
cc
Right-handed, curly hair, attached ear lobe
EE
Detached ear lobe, straight hair, righthanded
Freckles
ddEeCC
Left-handed
aaCcdd
aaEE
Right-handed, straight hair, brown eyes,
attached ear lobe
Left-handed, attached ear lobe, freckles,
straight hair
Blue eyes, detached ear lobe
Left-handed, straight hair
Eedd
aaBbCCdd
Brown eyes, curly hair, attached ear lobe,
right-handed
Summary: Genetics Joins Evolutionary Theory

Traits are controlled by genes, which are inherited during reproduction.

A population can be thought of as a gene pool.

Evolution acts on phenotypes, but as a result influences the frequency of genotypes. Natural selection
works on an organism’s phenotype (traits or characteristics) not its genotype. For many traits, the
homozygous genotype (AA, for example) has the same phenotype as the heterozygous (Aa) genotype. If
both an AA and an Aa individual have the same phenotype, the environment cannot distinguish between
them.

Some alleles (forms of a gene) can increase or decrease based on changing pressures from the environment.
(New disease, predator, climate shift)
http://www.pbs.org/wgbh/evolution/educators/lessons/index.html
http://www.pbs.org/wgbh/evolution/darwin/origin/index.html
http://www.pbs.org/wgbh/evolution/change/family/
http://www.pbs.org/wgbh/evolution/educators/lessons/lesson3/index.html
Single Gene traits
Polygenic traits
May have 2 or 3 phenotypes
that can shift in frequency
based on environmental
pressure
Blood type, # of fingers, snail
shell pattern (p485)
Has a wide range of
phenotype expression that
can distribute in a bell shaped
pattern
Height, birth weight, skin
color,
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