Genetics
What is an ALLELe?
• Different form/version of a
gene
• You inherited ONE ALLELE
from each parent for each
trait.
• For example –
•Gene = eye color
•Allele = blue, hazel,
brown, and green
Dominant vs. Recessive Alleles
• Dominant allele hides the
recessive allele.
– The Dominant allele always shows/is
visible
– For example – hair color – brown is
dominant to all other hair colors
– EX: mom gave you the allele (gene) for
brown hair. Dad gave you the allele for
blonde hair.You will have what color hair?
– Answer: Brown hair
Dominant vs. Recessive Alleles (Cont.)
• Recessive allele is always hidden if a
dominant allele is present.
• You must inherit 2 recessive alleles for
the trait to show up/become visible.
– EX:– hair color – blonde is recessive
to all other hair colors
– mom has to give you the allele
(gene) for blonde hair and dad gave
you the allele for blonde hair, you
will have blonde hair!
Writing Alleles?
• All alleles are assigned letters
• Dominant allele=CAPITAL
letters
– B=(Brown eyes)
• Recessive allele – lower case
– b= (blonde eyes)
• Two letters pair for each trait – one passed on
from mom and one from dad
• Using the letter B tell me what a person with
brown hair would look like
– BB_____
– Bb_____
– bb_____
• Is this trait dominant or recessive?
– DOMINANT
• What if the person had blonde hair (recessive
trait)?
– bb
How you get your traits?
• Dimples are a dominant trait. Non
dimples are recessive. If both
parents have have dimples would all
the kids have dimples?
Genotype vs. Phenotype
• Phenotype- physical
trait
– can be seen
– Brown or blonde
• Genotype- genetic
makeup
– Alleles inherited
– (not seen BB, Bb)
Genotype/Phenotype Practice
• Are the following
genotype or
phenotype
• Hazel Eyes.
– Phenotype
• BB
– Genotype
• Long Toes
– Phenotype
• Rr
– genotype
• Tt
– genotype
• Ear Hair
– Phenotype
• Ff
– genotype
• Freckles
– phenotype
Homozygous vs Heterozygous
• PREFIXES:
– HOMO=SAME alleles for a specific trait
( TT or tt)
– HETERO=DIFFERENT alleles for a specific
trait (Tt or Bb)
Practice• 1.) If you inherited the 2 alleles for blue
eyes (1 from each parent), your phenotype
is __________, your genotype is _____,
and you’re _____ zygous.
• 2.) If you inherit the dominant allele for
dimples from your dad, and the recessive
for no dimples from your mom, your
phenotype is ______, your genotype is
_______, and you’re ____ zygous.
Practice Problems
Will the following plants be tall or short?
T=tall and t=short
Tt
TT
tt
Are the following plants homozygous or
heterozygous?
TT
Tt
tt
Practice
What is the phenotype of the
following plants?
Tt
TT
tt
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Genotype codes for Phenotype.
P = Purple and p= white
Y = Yellow and y = green
R = Round and r = wrinkled
Genotype is RR, the Phenotype is ______.
Genotype is YY, the Phenotype is ______.
Genotype is pp, the Phenotype is ______.
Genotype is Rr, the phenotype is ______.
Genotype is Yy, the phenotype is ______.
Phenotype is wrinkled, the genotype is ____.
Phenotype is green, the genotype is _____.
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Genotype codes for Phenotype.
P = Purple and p= white
Y = Yellow and y = green
R = Round and r = wrinkled
Genotype is RR, the Phenotype is ______.
Genotype is YY, the Phenotype is ______.
Genotype is pp, the Phenotype is ______.
Genotype is Rr, the phenotype is ______.
Genotype is Yy, the phenotype is ______.
Phenotype is wrinkled, the genotype is ____.
Phenotype is green, the genotype is _____.
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. Write dom. For dominant or rec. for recessive next the letter.
A ______
C ______
d _______
e _______
F _______
f ______
v ______
P ______
m ______
M ______
Q _______
n ________
b ________
X ________
Y _________
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. Write Ho. for homozygous or He. for heterozygous.
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AA _____
Bb ____
Cc ____
DD _____
eE _____
Ff ____
Gg ____
Hh ____
Kk ____
Mm ____
Nn ____
RR ____
Ss ____
NN ____
• . Write Ho. Dom if it is homozygous dominant, Ho. Rec. if it is
homozygous recessive or He if it is Heterozygous.
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AA ____
BB ____
Cc ____
dd ____
FF ____
qq ____
SS ____
TT ____
VV ____
Tt ____
uu ____
WW ____
ii ______
xx ____
bb ____
Law of Segregation
•What is segregation
– separation of alleles
•When does this occur?
–During meiosis (formation of sex cells)
•Why do they segregate?
–So each gamete only carries a single copy of each gene.
Law of Independent Assortment
• What is independent assortment?
– Genes/alleles separate independently during
meiosis.
– Genes don’t influence inheritance of other
genes
•(Inheriting blue eyes doesn’t mean you’ll
automatically inherit blonde hair)
•Seed color does not influence seed shape
• Dihybrid Crosses (2 trait punnet square)
demonstrates this law.
More on genetics….to be
continued.
Hot Celebrities’ alleles
• Think of the hottest looking male/female
celebrities you can think of.
• Write their names. Next to their names list
the 3 alleles they have that make them so
attractive.
• Be prepared to share your PG-13 rated
alleles 
Mom &/or Dad got it But you don’t
• Picture what your parents look like
• List some traits one or both parents have
but you don’t. For ex: eye color, hair color,
attached ear lobes, dimples, tall, short,
etc.
• You may have inherited some traits but
they’re hidden. Here is why………