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Genetics
Genetics is the study of
HEREDITY
Mendel and Heredity
Heredity is the passing of traits from
parents to offspring.
The beginnings of Genetics
Gregor Mendel
Gregor Mendel
Gregor Mendel
1822-1884
Gregor Mendel was
an Austrian Monk.
He worked with pea
plants to discover
several rules that
predict the patterns of
traits.
The Life of Mendel
Mendel was born in 1822 in Austria. At age 11
he was sent to a private school to continue his
studies. When he graduated from school he
attended the University of Olmutz where he
studied math and physics. After his graduation
In 1843 his father wanted him to
take over the family farm, but he
joined the Augustinian order at
the St. Thomas Monastery in
Brno to become a monk.
The monastery paid for him to continue his
studies at the University of Vienna. When he
finished his studies in 1853 he become a
secondary science teacher and began his
experiments. Around 1854 Mendel began
researching the transmission of traits in
plants.
At the time it was thought that the traits in
offspring were simply a blending of the traits
in the parents. They thought that after several
generations a hybrid would revert to its
original form.
Mendel’s choice of plant research was
important because pea plants have traits that
come in two distinct versions. Pea plants are
also easy to grow and reproduce.
Experiments
Used pea plants
because they grow and
reproduce quicklyeither self pollinate, or
cross pollinate
Crossed pea plants:
short with short and
tall with tall
Led to the discovery
of dominant and
recessive traits
Mendel’s Law of Segregation
Organisms contain two alleles for each trait.
An allele is a specific form of a gene. The
two alleles for each trait separate during
meiosis.
When gametes (sex cells) combine during
fertilization the offspring will have two alleles
for each trait.
Segregation of alleles in the
production of sex cells
Not in Notes….
Reshuffling genes explains variations and
why offspring differ from their parents.
More precisely the law states that when any
individual produces gametes, the copies of a
gene separate so that each gamete receives
only one copy (allele). A gamete will
receive one allele or the other randomly at
fertilization.
Mendel’s Law of Independent
Assortment
A random distribution of alleles occurs
during Metaphase I. Genes of separate
chromosomes sort independently during
gamete formation.
Not in notes
As such, the gamete can end up with any
combination of paternal or maternal
chromosomes. Any of the possible
combinations of gametes formed from
maternal and paternal chromosomes will
occur with equal frequency.
Not in notes…
For human gametes, with 23 pairs of
chromosomes, the number of possibilities is
223 or 8,388,608 possible combinations.
The gametes will normally end up with 23
chromosomes, but the origin of any
particular one will be randomly selected
from paternal or maternal chromosomes.
This is why the human inheritance of a
particular eye color does not increase or
decrease the likelihood of having 6 fingers
on each hand. The genes are separate
chromosomes.
Overview of heredity and
independent assortment
independent
assortment
Genetic
Vocab Words
Alleles
 Letters
of
the
alphabet
 Code for a
trait
 One from
father
 One from
mother
Dominant Trait
“Dominates”
 Shows in the
outward
appearance
 Even when
recessive trait
is present

Bb
BB
or
Bb
Recessive Trait
Albinism
bb
 “hidden”
 May
be
masked
by a
dominant
trait
Bb
Dominant
Allele:
Recessive
Allele:
 Upper
 Lower
case
letter of
the
alphabet
 Codes for
dominant
traits
case
letter of
the
alphabet
 Codes for
recessive
traits
Genotype
Allele set
 True genetic
makeup of the
chromosome

Phenotype
 Outward
appearance
 Trait that is
shown
 Bb looks
brown (has
“b” =white
allele)
Composite Sketch
Homozygous:
Pure condition,
2 same case alleles
 Dominant: BB
 Recessive: bb
Hybrid:
An offspring resulting from
cross-breeding. The blending of
traits.
1.
2.
3.
Lion+tiger=Liger
zebra+donkey=zonkey
Jaguar+lion= Jaglion
Carrier
a
person or
organism that has
inherited a genetic
trait or mutation,
but who does not
display that trait or
show symptoms of
the disease.
P: parental
generation
 The
beginning
generation, the
parents of the F1
generation…
F1:

Genetic Cross
Mating between
2 parental lines
producing the
1st “filial”
generation
F 2:

Children of
the cross
between
the children
of an F1


F1=
B
B
b
Bb
Bb
b
Bb
Bb
F2=
B
b
B b
BB Bb
Bb bb
Filial comes from a Latin
word that means son or
daughter.
Monohybrid Cross
 Cross
for one
trait
 Example:
Hair color
Bb
B BB Bb
B BB Bb
Punnet Square
Dihybrid Cross
parents

Cross with
two traits,
2 types of
alleles
Children Children Children Children
Children Children Children Children
Children Children Children Children

1.
2.
Example:
Hair Color
Eye Color
Children Children Children Children
Probability
“Likelihood” Lab
First:
Collect the data using 1 coin
and 2 coins flipping them 50
times and recording your
results.
Probability Formula:
Total # of Outcomes_______
Total # of ALL possible outcomes

If you have a coin, and you flip
it, what is the chance it will be
heads? Tails?
Probability Lab Questions



What does probability have to do with
genetics?
What is the chance of having a boy?
What is the chance of having 3 in a row?

Biologists began to use probabilities
to determine how likely a specific
event would occur. They would set up
punnett squares.
Punnett Square Practice
1.
T
t
2.
t
a
t
a
A
A
Pea plants that produce round seeds are
crossed with those that produce
wrinkled seeds. The progeny are selffertilized. Diagram the cross.
P: RR x rr
Phenotype Ratio
Dominant Trait: Recessive Trait
____________:_____________
Genotype Ratio
Homozygous Dominant: Heterozygous: Homozygous Recessive
______________ : __________ : ____________
2. If red is dominant and white is recessive
and pink flowers are produced when they
are crossed, what would be the expected
ratio of phenotypes when two pink flowers
are crossed?
Codominance
Neither allele is dominant and both
alleles are expressed. Both alleles are
displayed at the same time.
EX. With codominance in flowers, the
resulting offspring between red and
white parents would not be pink.
Instead, they would be red with white
spots or white with red spots, the
result of both colors being
codominant.
Incomplete Dominance
The heterozygous phenotype is new. When
neither gene is completely dominant.
Alleles blend to create a new phenotype.
RR=red
rr= white
Rr=pink
Cross a RR x rr
What is the genotypic ratio?
Hybrid is a
blend of traits
 Example:

RR=red
Rr=pink
rr=white
Pink Carnation
Which one is which?
1.
2.
Multiple Alleles

Having more
than two
alleles for a
specific trait.
Example:
Blood Type

 TYPES:
A
A
I I ,
A
I i
A
B IBIB , IBi
AB IAIB
O
ii
Polygenic traits
When more then one gene codes for a
certain trait.
Ex. Hair and Eye Color
Sex-Linked Traits
Trait controlled by
genes located on the
x chromosome
 Males are affected by
sex linked traits more
often because they
only have one!

XY male
XXFemale
 8%
of men and 0.5% of
women have some form of
deficiency (red-green).
 A.K.A: protanopia (redblindness),
Normal
red-green
Fruit Fly Matting's
Pedigree Charts
A pedigree is a chart of the
genetic traits of a family over
several generations.
Pedigree Charts

Female =

Male=

Sexual Union=

Offspring=
Carrier =
Affected =
or
Draw your own Family Pedigree
Chart.
Add the following to your
pedigree:
Mom and Dad are both carriers
Brother or sister is affected
Pedigree Chart -Cystic Fibrosis
Question Time
Genetic Diseases
1.
Sickle Cell Anemia: Caused by a
faulty protein. Recessive disease.
Causes poor blood circulation.
1/500 African Americans
N = dominant normal gene
S = abnormal recessive gene
NN = normal
Ns = carrier
ss = abnormal for sickle cell anemia
Cross homozygous dominant with a
heterozygous. What is the
phenotypic and genotypic ratio?
2. Tay Sachs
Deterioration of central nervous
system. Defective enzymes due to
mutations. Usually don’t survive into
adult hood 1/1600 Jewish origin
E = normal
t = abnormal for tay sachs
EE = Normal
Et = Carrier
tt = abnormal
Et-possible
tt-not likely to
reproduce
Cross a
heterozygous with
a homozygous
dominant. What is
the phenotypic and
genotypic ratio?
3. Cystic Fibrosis
CF-defective protein in the pancreas.
Body produces too much mucus. Very
thick-die of pneumonia. Usually die of
2nd effects-Mucus clogs lungs, liver, and
pancreas.
C = normal
f = abnormal for CF
CC = normal
Cf = carrier
ff = abnormal
Cross two heterozygous individuals.
What is the phenotypic and
genotypic ratio?
You need to look up information
on the following diseases.
What are they? Are they
dominant? Recessive?
4. Marfan Syndrome
5. Achnodroplasia
(dwarfism)
Alex the Life of a Child
Dihybrid Crosses pg. 11
Cross
A-dimples
B-Right
AaBb x AABB
a- no dimples
b-left
1. What is
the
phenotypic
ratio for
each trait?
Examples



Back to our example of the pink
flower, the red and white traits passed
on by each parent are the alleles.
The combination of each parents allele
(red or white) forms the gene.
A group of genes forms a
chromosome.
Human Blood Type
There are 3 alleles for blood
type: A, B, O
Each of us has two ABO blood
type allele, because we each
inherit one blood type allele
from our mother and one from
our father.
There are a total of six different
allele genotypes for blood type.
Each group is represented by a
substance on the surface of red
blood cells.
A Blood has A-Antigens
Review: Vocabulary Terms




Dominant trait in genetics is the
stronger trait in genetics
Recessive trait is the weaker trait in
genetics
Genotype is the genetic makeup of an
organism
Phenotype is the visible characteristics
of an organism
Vocabulary Terms



Chromosome: a rod shaped cell
structure that directs the activities of a
cell and passes on the traits of a cell
to new cells
Gene: basic unit of heredity
Allele: each form of a gene