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Genetics
11.1 –
Gregor
Mendel
Heredity
 Inheritance

of traits
- study of heredity
Genetics
Gregor Mendel
 Suggested
that paired factors,
or
, carry inherited traits.

how traits were
inherited by studying pea plants
The Role of Fertilization
- During sexual reproduction,
male and female reproductive cells
to
produce a
cell.
The Role of Fertilization
The Role of Fertilization
•
Mendel had several
-breeding plants
•
•
Self-pollinating and
produce offspring
to parent
- a specific
characteristic of an individual
•
•
_
Ex) Seed color and shape.
Varies
The Role of Fertilization
•
•
Mendel studied traits of pea plants.
- Offspring between parents with
different traits.
Genes and Alleles

gen –
- Original pair of plants
•
- Offspring of
generation.
•
In each cross, the nature of the other parent,
with regard to each trait, seemed to have
.
Genes and Alleles
Mendel’s first conclusion • An individual’s
are
by factors that are
from one
parental generation to the next.
•
•
- Factors
that are passed from
parent to offspring.
Dominant and Recessive Traits
•
Mendel’s second conclusion
–
Some alleles are dominant, others are recessive.
• If an organism has at least
allele for a trait,
it will exhibit the dominant trait.
• If an organism has a
allele
for a trait, it will exhibit the recessive
trait only when there are
alleles present.
•
Alleles
forms of a gene
 Organisms have
alleles,
or genes, for each trait.
 One allele from the
gamete (egg).
 One allele from the
gamete (sperm).

Segregation
•
What happened to the
recessive alleles?
•
Mendel allowed
hybrids
to self-pollinate. The
offspring of an F1 cross are
called the
generation.
The F1 Cross
•
When Mendel saw the
plants, he observed the
recessive traits
.
•
About
of the F2 plants
showed the recessive trait.
_
Explaining the F1 Cross
•
Alleles had
•
Mendel suggested the alleles for tallness and
shortness in the
plants segregated from each
other 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)
of two genes

 Represented
 Written
by
letter
first
 Example:
for tall plant height
Recessive gene (allele)
of two genes

 Can
be
 Represented
 Example:
by dominant genes.
with
for short plant height
letters
Pure (Homozygous)
 Two
of the
trait
 Example:
(homozygous
(
genes (alleles) for a
) or
recessive)
Hybrid (Heterozygous)
 Two
alleles for a trait
 Example:
 Tall
or short?
Probability

– The likelihood
that a particular 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
or genes for a
Phenotype
, visible traits

how
it looks
 Determined
 Example:
by looking at organism
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
What are the phenotypes of the
parent plants?
If both parents are pure, what
are their genotypes?
Which gene or allele can each
parent pass on to the
offspring?
What is the phenotype of the
offspring?
What is the genotype of the
offspring?
All tall plants
In pea plants, round pea pod texture is
dominant over wrinkled texture.
What is the genotype of the following?
homozygous
round
heterozygous
wrinkled
pure dominant
hybrid round
In pea plants, round pea pod texture is
dominant over wrinkled texture. What is
the genotype of the following?
pure
recessive
heterozygous round
pure wrinkled
hybrid
pure round
Punnett Squares
 Punnett
squares –
used to
and compare the
genetic differences
that will
from a
cross.
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 in a cross.

Ex) Cross a male and female bird that are
heterozygous for large beaks. They each
have genotypes of Bb.

Bb and 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 for different traits can
independently during the formation of
gametes.
–
Dihybrid Cross
 Two

factor cross
involved.
The Two-Factor Cross: F1

Mendel crossed two
true-breeding plants:

One produced only
peas

One produced only
peas.
The Two-Factor Cross: F1
The
peas had
the genotype
,
which is homozygous
.
The Two-Factor Cross: F1
The
peas
had the genotype
, which is
homozygous
.
The Two-Factor Cross: F1
 All
F1 offspring were
peas. Shows yellow
and round alleles are
over the alleles
for green and wrinkled.
 Punnett
square shows genotype
of F1 offspring as
,
for both seed shape and seed
color.
The Two-Factor Cross: F2
 Mendel
then crossed
the
plants to
produce
offspring.
 Crossed
with
Dihybrid cross instructions
 Cross
the
parent alleles.
Mom
 Make
sure each
box has two of
each letter,
one from each
parent
Dad
The Two-Factor Cross: F2
 Alleles
for shape
segregated
of those for color.
 Genes
that segregate
independently
each
other’s inheritance.
The Two-Factor Cross: F2
 Results
were close to the
ratio the Punnett
square predicts.
 Mendel
discovered the
principle of
–
genes for different traits
segregate independently
during gamete formation.
11.3 Other
Patterns of
Inheritance
Incomplete dominance
 Alleles
(mix)
 Neither gene is dominant

phenotype
is a blend of the dominant and
recessive phenotypes.
 Think
Red
about colors of paint
+ White = Pink
Dominance
www.nerdscience.com
11-3
Codominance
alleles are dominant


expresses both phenotypes together.
 There is NO “blending”
Red
+ White = Red and White
 Red
cow crossed with white cow results in
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 two or more (

Polygenic traits often show a
of phenotypes.

) genes
example: human skin color employs more than
four different genes
 Skin
color genes: AaBbCcDd
Genes and the Environment

The characteristics of any organism are
determined
by the genes that organism
inherits.

Genes provide a plan for development, but
how that plan unfolds also depends on the
environment.

Both
14.1 – Human
Chromosomes
Karyotype
of chromosome
arranged by decreasing size.
 Shows unusual number of chromosomes
 Can detect trisomy 21 (Down syndrome)
 Identifies male or female
 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
inherited on X and Y chromosomes.
 Most
are on the
bigger)
chromosome (because it’s
 Example)
Color blindness is a recessive
sex-linked trait on the X-chromosome

 Why?
show
traits more than females
Sex-linked Traits
 Males
get only
chromosome
Therefore,
males show
recessive
sex-linked traits on X chromosome.
 Females
have a second X chromosome
that carries another allele that can hide
recessive traits
Sex-linked Traits
 Females
who have recessive alleles
but show the dominant trait
(heterozygous) are called
 A woman can have normal vision but
the recessive
for
colorblindness
X-Chromosome Inactivation

If just one X chromosome is enough for male
cells, how does the cell “adjust” to the extra X
chromosome in female cells?

In female cells, one X chromosome is randomly
switched off, forming a
.

Barr bodies are generally not found in males
because their
chromosome is
still active.
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.