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Genetics
11.1 –
Gregor
Mendel
Heredity
 Inheritance

of traits
- study of heredity
Genetics
Gregor Mendel
 Suggested
carry inherited traits.

how traits were
inherited by studying pea plants
The Role of Fertilization
reproductive cells
a
- male and female
to produce
cell.
The Role of Fertilization
The Role of Fertilization
•
-breeding plants
•
•
- a specific
characteristic
•
•
Produce offspring
to parent
Ex) Seed color and shape.
Varies
The Role of Fertilization
•
- Offspring of parents
with different traits.
Genes and Alleles

•
•
gen –
- Offspring of
generation.
In each cross, one parent’s traits seemed to
have
.
Genes and Alleles
•
are
by genes
that are
from
parents to offspring.
Dominant and Recessive Traits
•
–
Some alleles are dominant, others are recessive.
•
Express dominant trait if at least
allele is present.
•
Express recessive trait if
alleles present
•
Only recessive alleles present.
Alleles

 Organisms
have
for each trait.
 One from
 One from
forms of a gene
alleles
.
.
Segregation
•
•
•
What happened to the
recessive alleles?
hybrids self-pollinate.
Offspring of F1 called
generation.
The F1 Cross
•
In
plants, recessive
traits
.
•
of F2 plants had
recessive trait.
Explaining the F1 Cross
•
Alleles segregated, or
during formation of the
sex cells, or
,
.
Recessive attached ear lobes
Dominant Free Ear Lobes
Tongue Roll
Dominant trait
Hitch hiker’s
thumb
Dominant
Regular thumb
Recessive
Seed Seed
shape color
Flower
color
Flower
position
Pod
color
Pod
shape
purple
axial
(side)
green
inflated
white
terminal
(tips)
yellow
Plant
height
Dominant
trait
round
yellow
tall
Recessive
trait
wrinkled
green
constricted
short
11.2 –
Applying
Mendel’s
Principles
Dominant gene (allele)
gene

 Represented
 Written
by
letter
first
 Example:
for tall plant height
Recessive gene (allele)
gene


 Represented
 Example:
if dominant genes present.
with
for short plant height
letters
Pure (Homozygous)
 Two
of the
for a trait
 Example:
(homozygous
(
genes (alleles)
) or
recessive)
Hybrid (Heterozygous)
 Two
alleles for a trait
 Example:
 Tall
or short?
Probability
– The likelihood

that an event will occur.
 Example:
Flipping a coin
 Probability
1
of flipping heads?
Number of
outcomes
Number of total
outcomes
2
Probability
 Example:
Flipping a coin
Probability of flipping heads three
times?
½
x½x½=
Genotype
 Combination
certain trait
 Example:
of
for a
Phenotype
 How
it physically looks
 Example:
Genotype or Phenotype?
 Tt
 Round
 Black
 BB
 Smooth
 rr
 Tall
In pea plants, green (G) pods are
completely dominant over yellow (g).
What are the genotypes?
 Homozygous
yellow
 Heterozygous green
 Homozygous dominant
 Hybrid
In pea plants, green pods are
completely dominant over yellow.
 Pure
yellow
 Homozygous
 Pure
recessive
green
 Heterozygous
 Yellow
In guinea pigs, short hair is
dominant over long hair
 What
hair length will be represented by
a capital S?
 What
hair length will be represented by
a lower case s?
What phenotypes would result
from the following genotypes?
 SS
 ss
 Ss
Phenotypes of parents?
If both parents are pure, what
are their genotypes?
Which allele will each parent
pass on to offspring?
Phenotype of offspring?
Genotype of offspring?
All tall plants
In pea plants, round is dominant
over wrinkled texture.
What is the genotype of the following?
homozygous
round
heterozygous
wrinkled
pure dominant
hybrid round
In pea plants, round is dominant
over wrinkled texture. What is the
genotype of the following?
pure
recessive
heterozygous round
pure wrinkled
hybrid
pure round
Punnett Squares
 Punnett
cross.
squares –
the
from a
Monohybrid
crosses
Heterozygous
tall parent
Heterozygous
tall parent
T
T
t
T t
T
t
t
How To Make a Punnett Square for a OneFactor Cross

Write the
parents.

Ex) Cross a male and female bird that are
heterozygous for large beaks.
Genotypes of Bb.

Bb x Bb
of the
How To Make a Punnett Square

Draw a Punnett square.

Put one parent on the
one parent on the

Put one
from each
parent on each side of each section.
,
.
How To Make a Punnett Square
Fill in the table by combining the gametes’
genotypes.
Mom
Dad
How To Make a Punnett Square
-Determine the genotypes and phenotypes of
each offspring.
Probability of having…
A
large beak?
A
small beak?
 Homozygous
dominant?
 Heterozygous?
 Homozygous
recessive?
Independent Assortment
–
Principle of
genes
independently.
One gene
effect another.
I.e. - Hair color does not effect eye color.
Dihybrid Cross
 Two

factor cross
involved.
The Two-Factor Cross: F1

Cross two
true-breeding plants:

One produced only
peas

One produced only
peas.
The Two-Factor Cross: F1
peas had
genotype
-Homozygous
.
The Two-Factor Cross: F1
peas
had genotype
- Homozygous
The Two-Factor Cross: F1
 All
F1 offspring were
.
 Shows
yellow
and round alleles are
over
green and wrinkled.
 Punnett
square shows genotype of
F1 offspring as
,
for both seed shape and seed color.
The Two-Factor Cross: F2
 Crossed
produce
 Crossed
plants to
offspring.
with
Dihybrid cross instructions
 Cross
the parent
alleles.
 Outside
has
of each allele
has
alleles, two from
each parent
Mom
 Inside
Dad
The Two-Factor Cross: F2
 Different
genes
each
other’s inheritance.
The Two-Factor Cross: F2
 Dihybrid
cross has
ratio.
 Principle
of
–
genes for different traits
segregate independently.
11.3 Other
Patterns of
Inheritance
Incomplete dominance
 Alleles
(mix)
 Neither gene is dominant

phenotype
is a blend.
 Like
colors of paint
Red
+ White = Pink
Incomplete
Dominance
R
R
W
W
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11-3
Codominance
alleles are dominant


expresses both.
 There is NO “blending”
Red
+ White = Red and White
 Red
cow + white cow = roan cattle.
Roan cattle have
hairs.
Codominance
Codominance
 Example:
 White
chicken
(WW) x black
chicken (BB) =
black and white
checkered chicken
(BW)
Codominance
Incomplete or Codominance?
A
white cow and a red cow produce a
roan cow, one that has both white and
red hairs.
A
red flower and a white flower produce
pink flowers.
A
black cat and a tan cat produce tabby
cats, cats where black and tan fur is seen
together.
Incomplete or Codominance?
A
blue blahblah bird and a white blahblah
bird produce offspring that are silver.
A
certain species of mouse with black fur is
crossed with a mouse with white fur and
all of the offspring have grey fur.
A
woman with blood type A and a man with
blood type B have a child with blood type
AB.
Multiple Alleles
 Single
gene with
alleles.
 example:
type
human blood
Blood Types (codominant)
 Blood
type is
codominant

and
are
dominant.

is recessive
 4 different blood
types
Phenotype Genotype
(Blood
(Alleles or
type)
genes for
blood type)
A
IAIA, IAi
B
IBIB, IBi
AB
IAIB
O
ii
Polygenic Traits

Traits controlled by


genes
of phenotypes.
example: human skin color has
four different genes
 Skin
color genes: AaBbCcDd
Genes and the Environment
 Genes
provide a plan for development, but
also depends on the environment.

Both
14.1 – Human
Chromosomes
Karyotype
of chromosome
 Shows
– full set of
genetic information.

.
Karyotype
Normal Female
Karyotype
Female with Down Syndrome
Sex Chromosomes
chromosomes
 Determine the sex of the offspring
 Females are
 Males are

Sex Chromosomes
 All
other chromosomes are
.
 Everyone has 46 chromsomes:
sex chromosomes and
autosomes.
Sex-linked Traits
 Traits
 Most
inherited on X and Y chromosomes.
on
chromosome
 Ex)
Color blindness recessive
sex-linked trait on X-chromosome
show

females
traits more than
Sex-linked Traits
 Heterozygous
females are
X-Chromosome Inactivation

In female cells, one X chromosome is randomly
switched off, forming a
.

Not found in
one X chromosome.
because only have
Pedigree Study
 Method
of determining the genotype
of individuals by looking at
Male
Parents
Female
Siblings
Affected
male
Affected
female
Mating
Known
heterozygotes
for recessive
allele
Death
Pedigrees
illustrate
inheritance
Human Pedigrees

This diagram shows what the symbols in a
pedigree represent.
Human Pedigrees


This pedigree shows how one human trait—a
white lock of hair just above the forehead—
through three generations of a family.
The allele for the white forelock trait is
.
Human Pedigrees

Top of the chart is grandfather with the white
forelock trait.

of his
inherited the trait.

but
children
grandchildren have the trait,
do not.
Human Pedigrees

Because the white forelock trait is dominant, all
family members lacking this trait must have
alleles.

One of the grandfather’s children lacks the white
forelock trait, so the grandfather must be
for this trait.