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Genetics
I. Introduction to Genetics
A. Heredity is the passing
on of characteristics
from parents to
offspring.
• *Genetics- science of
heredity
B. Gregor Mendel- father of
genetics
1. Studied pea plants
– Why? Grow easily, produce
large #s of offspring, pollen
can be transferred to different
plants.
2. Predicted how traits are
transferred from one
generation to the next.
3. Concluded that each
organism inherits a gene for
a particular trait from each
parent. Genes have different
forms called alleles.
–Ex. Height is the gene. The
alleles are tall and short.
C. Mendel’s Laws or Findings
1. Law of Unit Factors- an
organism inherits 2 alleles
for each trait.
2. Law of Dominance- one
allele may mask or cover the
other.
Ex. The tall allele is dominant
over the short.
3. Law of Segregation- During
meiosis, homologous
chromosomes separate
from each other and an
offspring inherits one allele
for a trait from each parent.
4. Law of Independent
Assortment- genes for different
traits are inherited
independently from each
other.
Ex. Round yellow seeds, green
wrinkled seeds, wrinkled
yellow seeds, round green
seeds.
-colors & texture come from
different alleles
II. Punnett Square
A. Dominant alleles
are represented by
a capital letter.
(Tall allele= T)
Recessive alleles
by a lowercase
letter (short= t)
B. An organism is
homozygous for a trait
if its two alleles for a
trait are the same.
– TT is homozygous
dominant (tall)
– tt is homozygous
recessive (short)
C. An organism is
heterozygous for a trait if
its 2 alleles for a trait are
different. Ex. Tt
D. Two organisms can look alike
but have different gene
combinations. TT vs. Tt
– The way an organism looks is
called its phenotype.
– The gene combination an
organism contains is called
its genotype.
Phenotype & Genotype
Example- Eye color:
– brown eyes are
dominant to
other colors so…
Phenotype: brown
Genotype: BB or Bb
E. A Punnett Square is a
way of finding the
possible genotypes in
the offspring of a cross.
1. The basic p-square looks like
a window pane.
2. Review- In a type of bird a
red throat is the dominant
trait and white throat is
recessive.
Symbol
Genotype
Name
Phenotype
RR
homozygous
dominant
red throat
Rr
heterozygous
dominant
red throat
rr
homozygous
recessive
white throat
3. Basic steps to a making a
Punnett square.
a. Determine the genotypes of
the parents.
b. Write down the cross.
(genotype)
c. Draw a p-square.
d. Split the letters of the genotype
for each parent and put them
outside the square.
e. Determine the possible genotypes
of the offspring by filling in the psquare.
f. Summarize results (phenotypes
and genotypes of the offspring)
F. Examples of monohybrid
crosses (when only 1 trait is
studied)
1. Example: You cross a
white-throated bird with a
homozygous (hom) dominant
red-throated bird. What are
the possible offspring?
a. White is rr and hom
dominant is RR.
b. rr x RR
c.
r
r
R
R
d. The offspring will all be redthroated and heterozygous.
-100% red-throated; 100%
Rr
2. Example: In pea plants, the
allele for tallness is
represented by the letter T.
The allele for shortness is t.
A short plant is crossed
with a heterozygous (het)
Tall plant. What are the
offspring produced?
a. short plant: tt; het plant
Tt
b. tt x Tt
c.
t
t
T
t
d. Phenotype: ½ plants tall, ½
plants short OR 1 tall: 1
short
- Genotype: ½ plants Tt
and ½ plants tt OR 1 Tt:
1 tt
3. Example: In guinea pigs,
black hair color is
dominant and brown is
recessive. Cross a brown
individual with a hom
dominant individual.
III. Complex Patterns of
Inheritance
A. Incomplete
dominance- neither
allele is dominant
and an
intermediate trait
is formed.
• Ex. Hom. Red
Snapdragon x
Hom. White
Snapdragon=
Heterozygous
Pink
Snapdragon
B. Codominance- when 1 allele
is not dominant over
another and both are
expressed equally
Ex. Black Feathered Chicken x White
Chicken =
Black and White Chicken
+
C. Multiple Alleles- when
more than 2 alleles control
a trait. Ex. Human blood
types
1. There are three
different alleles for human
blood type:
Blood
Type
Ia
We call
them
A
Ib
B
i
O
2. However, combinations of
these alleles will give someone
their blood type.
Blood Type
Genotype
A
IaIa
B
IbIb
AB
IaIb
O
ii
D. Sex- linked Inheritance
1. Traits that are
controlled by genes
located on sex
chromosomes are known
as sex-linked traits.
2. In humans, the diploid # is
46 (23 pairs)
a. 22 pairs of
chromosomes
as autosomes
are known
b. 1 pair is known a sex
chromosomes- these
determine sex
XX
XY
3. Males have a greater
chance of inheriting a
sex-linked trait.
4. Ex. Red-green
colorblindness, Hemophilia
E. Polygenic Inheritancecontinuous range of
phenotypes controlled by 2
or more genes. Ex. Skin
color, Eye color, Height
IV. TESTCROSSES & PEDIGREES
A.Testcrosses
1.Cross of individual of
unknown genotype with an
individual of known genotype
in order to determine the
unknown genotype
2. Usually the known test
organism is homozygous
recessive for the trait
3. Example
a. In guinea pigs, black coat
color is dominant (B) and a
brown coat is recessive (b).
a.What are the possible genotypes of a
black guinea pig?
b. What is the genotype of the brown
guinea pig?
c. If a black guinea pig is mated with a
brown guinea pig and all the offspring
are black, what is the genotype of the
black guinea pig parent? Show a
punnett to prove your answer.
d. What must be the genotype of an
unknown guinea pig if offspring of that
pig and a brown pig are all brown?
B. Pedigrees
1. Graphic representation of
an individual’s family tree
2. Uses
a. Predict the chances of
offspring receiving a trait
b. Determine the
inheritance pattern of a
particular trait
C.c.
Pedigree
Chart:ifshows
within a family
Know
an relationships
individual
& if individual
has gene
possesses
a given allele
Key:
Male
male
Female
female
carrier
affected
D. Karyotyping- using
“photographs” to examine
chromosomes. Can be used
to identify missing, broken,
or extra chromosomes.
VII. Dihybrid Crosses
Dihybrid cross: 2 traits
ex: TtYy x TTYY
(Tt) (Yy) = TY, Ty, Yt, ty
(TT) (YY) = TY, TY, TY, TY
TY
Ty
Yt
ty
TY
TTYY
TTYy
TtYY
TtYy
TY
TTYY
TTYy
TtYY
TtYy
TY
TTYY
TTYy
TtYY
TtYy
TY
TTYY
TTYy
TtYY
TtYy
1.Example:
Cross a pea plant that is homo dom for green
seeds & hetero for round pods with a plant
that has yellow seeds and hetero for round
pods.
GR
Gr
GR
Gr
gR
GgRR
GgRr
GgRR
GgRr
gr
GgRr
Ggrr
GgRr
Ggrr
gR
GgRR
GgRr
GgRR
GgRr
gr
GgRr
Ggrr
GgRr
Ggrr
Genotype:
GgRR – ¼ or 25%
GgRr – ½ or 50%
Ggrr – ¼ or 25%
Phenotype:
green seed, round pod – 75%
green seed, wrinkled pod – 25%
VI. Biotechnology
A.Manipulating DNA
1. Restriction Enzymes
a. Endonuclease
b. cut DNA at specific nucleotide sequences
c. blunt ends
d. sticky ends
2. Gel electrophoresis
a. once DNA is cut
has to be sorted
b. done according to size
c. moves toward + end b/c DNA is -
d. Small fragments move farther
e. Restriction map: shows length of DNA b/w
restriction sites
gel
B. DNA Fingerprinting
1. Looks at repeating DNA sequences
2. similar, but will not
all be the same
3. used in families, crime
scenes
C. Genetic Engineering
gene
1. clone: genetically
identical copy of a
a. take out nucleus
of
cell and replace
with nucleus of
another cell –
nuclear
transfer
2. controversial?
a. success rate is low
b. health problems
c. grow faster
d. expensive
4. Selective breeding: humans alter the genotype
and phenotype of organism
Ex: labradoodle
corn
5. Human Genome Project
a. 2 main goals:
in
- map & sequence all DNA base pairs
human chromosome
- identify all the genes within the
sequence
b. 13 year project: 1987-2003
g
g
In Squidward’s family, a blue body
color (B) is dominant to green (b).
Determine the phenotype for each
genotype below based on this
information.
BB _________________
Bb _________________
bb _________________
If tall eyeballs (T) are dominant to
short eyeballs(t), give the
genotypes that are possible for
members of Mr. Krabbs’ family.
Tall eyeballs = ___________________
Short eyeballs =__________________
SpongeBob is known for his big round eyes
(R), which is dominant over an oval eye
shape (r). If he is heterozygous for his round
eye shape and marries a woman with oval
eye shape, what type of eyes might the kids
have?
A. List the genotypes for each: Heterozygous
round eyes - _______ Oval eyes - _______
B. Complete the punnett square to show the
possibilities that would results if
SpongeBob had children with an oval-eyed
woman.
C. List the possible genotypes and
phenotypes for their children.
D. What are the chances of a child
with a round eye shape? ____%
E. What are the chances of a child
with an oval eye shape? ____%
List the phenotypes &
genotypes for the 4 types
of blood.
1.AB x O
2.O x B
3.B x B