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Applied Biology
Genetics Notes
Genetics Introduction
• Genetics is the study of heredity
• Heredity explains why you look like your
parents or siblings (similar traits)
• Traits (ex. Color, shape) are inherited or
passed down to offspring in genetic
crosses
Essential Vocabulary!
• Gene – parts of DNA that control traits
• Gregor Mendel – “Father of Genetics”, studied inheritable
information & performed plant-cross experiments
Dominant vs Recessive
Dominant gene – trait ALWAYS shows itself
Recessive gene – trait hidden when dominant
gene is present
Allele – forms of a particular gene (we use caps
& lower case letters)
(R = round and r = wrinkled…….but
both code for shape)
Homozygous vs.
Heterozygous
• Homozygous – 2 of same allele for a trait
(RR or rr)
• Heterozygous – 2 different alleles for a
trait (Rr)
Phenotype vs. Genotype
Genotype
• Phenotype –
physical observable
trait (shape, color
ect.)
• Genotype – genetic
make-up,
combination of
alleles (RR, Rr, rr)
Phenotype
(purple)
Solving Genetics Problems
1. Designate letters for traits
(R=Round, r=wrinkled)
2. Determine parent alleles
3. Set up Punnett square
4. Fill – in Squares
5. Determine possible offspring genotypes &
Phenotypes
Practice Problem
Black hair (B) is dominant over brown hair (b). A man
heterozygous for black hair and a woman with
brown hair have children. What are the genotypes
and phenotypes of their offspring?
Step #1
B = black
Step #2 Dad =
Step #3 (punnett square)
Step #4 (fill-in offspring squares)
Step #5 (Genotypes & phenotypes)
b = brown
Mom =
Blood Typing Genetics
(Codominance & Multiple Alleles)
• In simple genetics…there are usually 2 alleles
– 1 dominant (R) & 1 recessive (r)
• In Codominance…neither allele is dominant
over the other!
• Since they are COdominant…they both show up
in the heterozygous phenotype!
Blood Typing Genetics (cont.)
• Usually in simple genetics problems we have:
– 1 Dominant Allele
– 1 Recessive Allele
R
or
r
• In Blood typing, we have:
–2 Dominant Alleles = A & B
–1 Recessive Allele =
o
EXAMPLE: Blood Types!
Blood Typing - Codominance
• In humans, there are 4 possible blood
types: A, B, AB, and O.
• Type O individuals are considered to be the “universal
donors”, whereas type AB individuals are said to be
“universal recipients”!
Blood Type Genotypes
Type A Blood
– AA is homozygous
– Ao is heterozygous
Type B Blood
– BB is homozygous
– Bo is heterozygous
Type AB Blood
– AB (this is the co-dominant blood type!)
Type O Blood
– oo (only 1 way to have Type O blood because o is
recessive!)
Blood Typing – Practice Problem
A man heterozygous for Type A blood and
woman homozygous for Type B blood have
children. What are the possible genotypes and
phenotypes of their offspring?
Practice Problem #2
Two babies are ready to go home from the
hospital…Which baby belongs to which parents?
• Here’s what you know about the babies:
– Baby A bas blood type A
– Baby B has blood type O
Parents #1 - Father (Homozygous Type A) &
Mother (Type O)
Parents #2 - Father & Mother (Heterozygous A)
Sex Linkage – Hemophilia
Some traits are carried on the X
chromosome!! Hemophilia is the most wellknown sex-linked disease!

Males = X Y
Females = X X
Hemophilia
Lacking the ability for blood to clot…can’t
stop bleeding 
Possible Genotypes:
Hemophilic Male Genotype = X Y
Hemophilic Female = X X
Normal Male Genotype = X Y
Normal Female Genotypes = X X
X X (CARRIER)
Practice Sex Linkage (Hemophilia)
Problem
A man with hemophilia and a normal women (but
carrier for hemophilia) have a child. What are the
possible genotypes and phenotypes of their
offspring?
Man = X Y
Woman = X X
Offspring Genotypes:
Offspring Phenotypes:
Human Genetics
Karyotype - the complete
set of chromosomes in a
species. Can show
chromosomal disorders
such as:
1.
Down Syndrome (Trisomy 21)
2.
Turner Syndrome (X missing
pieces)
3.
Klinefelter Syndrome (XXY)
Chromosomal Disorders occur due to NONDISJUNCTION –
error in meiosis where chromosomes don’t separate
correctly during anaphase!
Human Genetics - Pedigrees