Genetics
11.1 –
Gregor
Mendel
Heredity
 Inheritance
 Genetics
of traits
- study of heredity
Genetics
Gregor Mendel
 Suggested
that paired factors,
or genes, carry inherited traits.
 Predicted how traits were
inherited by studying pea plants
The Role of Fertilization
Fertilization - During sexual reproduction,
male and female reproductive cells join to
produce a new cell.
The Role of Fertilization
The Role of Fertilization
•
Mendel had several truebreeding plants
•
•
Trait - a specific
characteristic of an individual
•
•
Self-pollinating and
produce offspring
identical to parent
Ex) Seed color and shape.
Varies
The Role of Fertilization
•
•
Mendel studied traits of pea plants.
Hybrids - Offspring between parents with
different traits.
Quick Graded Review –
Two Options – 5 minutes


1. Stand and speak

Summarize the notes in 15 seconds.

Spend the next 3 minutes preparing what you’ll say.
2. Schoology discussion

Go to Schoology  your class  Unit 7 
11.1 Summary – First Half

Write a summary of the notes so far in at least 3
sentences.

Do not respond to anyone yet.
Genes and Alleles
P
gen – Parents - Original pair of plants
•
F1 - Offspring of P generation.
•
In each cross, the nature of the other parent,
with regard to each trait, seemed to have
disappeared.
Genes and Alleles
Mendel’s first conclusion • An individual’s
characteristics are
determined by factors that are
passed from one
parental generation to the next.
•
•
Genes - Factors
that are passed from
parent to offspring.
Dominant and Recessive Traits
•
Mendel’s second conclusion
• Principle of Dominance –
Some alleles are dominant, others are recessive.
• If an organism has at least
one dominant allele for a trait,
it will exhibit the dominant trait.
• If an organism has a recessive allele
for a trait, it will exhibit the recessive
trait only when there are
no dominant alleles present.
Alleles
 Different
forms of a gene
 Organisms have two alleles,
or genes, for each trait.
 One allele from the
female gamete (egg).
 One allele from the
male gamete (sperm).
Segregation
•
What happened to the
recessive alleles?
•
Mendel allowed F1 hybrids
to self-pollinate. The
offspring of an F1 cross are
called the F2 generation.
The F1 Cross
•
When Mendel saw the F2
plants, he observed the
recessive traits
reappeared.
•
About ¼ of the F2 plants
showed the recessive trait.
Explaining the F1 Cross
•
Alleles had segregated.
•
Mendel suggested the alleles for tallness and
shortness in the F1 plants segregated from each
other during formation of the sex cells, or gametes.
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
Quick Graded Review –
Two Options – 5 minutes


1. Stand and speak

Summarize this part of notes in 15 seconds.

Spend the next 3 minutes preparing what you’ll say.
2. Schoology discussion

Go to Schoology  your class  Unit 7 
11.1 Summary – Second Half

Write a summary of this part of notes in at least 3
sentences.

Or respond and add on to someone else’s response
from First Half with information from notes.
Recessive attached ear lobes
Dominant Free Ear Lobes
Tongue Roll
Dominant trait
Hitch hiker’s
thumb
Dominant
Regular thumb
Recessive
Other examples
 Chin
cleft – Dominant
 Bent
pinky finger – Dominant
 Dimples
 Blue
– Dominant
eyes – Recessive
 Hand
clasp – Left thumb dominant
 Widows
peak - Dominant
11.2 –
Applying
Mendel’s
Principles
Dominant gene (allele)
 Stronger
of two genes
 Represented
 Written
by capital letter
first
 Example:
T for tall plant height
Recessive gene (allele)
 Weaker
 Can
of two genes
be hidden by dominant genes.
 Represented
 Example:
with lower case letters
t for short plant height
Pure (Homozygous)
 Two
of the same genes (alleles) for a
trait
 Example:
TT (homozygous dominant) or
tt (homozygous recessive)
Hybrid (Heterozygous)
 Two
different alleles for a trait
 Example: Tt
 Tall or short?
Probability
 Probability
– The likelihood
that a particular event will occur.
 Example:
Flipping a coin
 Probability
1
of flipping heads?
Number of desired outcomes
2
Number of total possible outcomes
Probability
 Example:
Flipping a coin
Probability of flipping heads three
times?
½
x ½ x ½ = 1/8
Genotype
 Combination
of alleles or genes for a
certain trait
 Example: Tt, TT, tt
Phenotype
 Physical,
how
visible traits
it looks
 Determined
by looking at organism
 Example: tall, short
Genotype or Phenotype?
 Tt
Genotype
 Round
Phenotype
 Black
Phenotype
 BB
Genotype
 Smooth
Phenotype
 rr
Genotype
 Tall
Phenotype
In pea plants, green (G) pods are
completely dominant over yellow (g).
What are the genotypes?
 Homozygous
yellow gg
 Heterozygous green Gg
 Homozygous dominant GG
 Hybrid Gg
In pea plants, green pods are
completely dominant over yellow.
 Pure
gg
yellow
 Homozygous
recessive
 Pure
GG
green
 Heterozygous
 Yellow
gg
Gg
gg
In guinea pigs, short hair is
dominant over long hair
 What
hair length will be represented by
a capital S?
Short
 What
hair length will be represented by
a lower case s?
Long
What phenotypes would result
from the following genotypes?
 SS
Short hair
 ss
Long hair
 Ss
Short hair
What are the phenotypes of the
parent plants?
Tall plant
Short plant
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?
T
T
t
t
T
t
All tall plants
T
t
In pea plants, round pea pod texture is
dominant over wrinkled texture.
What is the genotype of the following?
homozygous
round RR
heterozygous
Rr
rr
wrinkled
RR
pure dominant
hybrid round
Rr
In pea plants, round pea pod texture is
dominant over wrinkled texture. What is
the genotype of the following?
pure
rr
recessive
Rr
heterozygous round
pure wrinkled
rr
hybrid
Rr
RR
pure round
Punnett Squares
 Punnett
squares –
used to predict
and compare the
genetic differences
that will result from a
cross.
Monohybrid
crosses
Heterozygous
tall parent
Heterozygous
tall parent
T
T t
T
t
t
T
TT
Tt
t
Tt
tt
How To Make a Punnett Square for a OneFactor Cross

Write the genotypes of 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
How To Make a Punnett Square

Draw a Punnett square.

Put one parent on the top,
one parent on the left.

Put one allele 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
3:4
1:4
dominant? 1:4
 Heterozygous?
 Homozygous
recessive?
2:4
1:4
Independent Assortment
Principle of independent assortment –
genes for different traits can segregate
independently during the formation of gametes.
Dihybrid Cross
 Two
factor cross
 Two traits involved.
The Two-Factor Cross: F1

Mendel crossed two
true-breeding plants:

One produced only
round yellow peas

One produced only
wrinkled green peas.
The Two-Factor Cross: F1
The round
yellow peas had
the genotype RRYY,
which is homozygous
dominant.
The Two-Factor Cross: F1
The wrinkled
green peas
had the genotype
rryy, which is
homozygous
recessive.
The Two-Factor Cross: F1
 All
F1 offspring were round
yellow peas. Shows yellow
and round alleles are
dominant over the alleles
for green and wrinkled.
 Punnett
square shows genotype
of F1 offspring as RrYy,
heterozygous
for both seed shape and seed
color.
The Two-Factor Cross: F2
 Mendel
then crossed
the F1 plants to
produce F2 offspring.
 Crossed
RrYy
RrYy 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
independently
of those for color.
 Genes
that segregate
independently do not
influence each
other’s inheritance.
The Two-Factor Cross: F2
 Results
were close to the
9:3:3:1 ratio the Punnett
square predicts.
 Mendel
discovered the
principle of
independent
assortment –
genes for different traits
segregate independently
during gamete formation.
11.3 Other
Patterns of
Inheritance
Incomplete dominance
 Alleles
BLEND (mix)
 Neither gene is dominant
 Heterozygous phenotype
is a blend of the dominant and
recessive phenotypes.
 Think
Red
about colors of paint
+ White = Pink
Incomplete
Dominance
R
R
W RW
RW
RW
RW
W
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11-3
Codominance
 Both
alleles are dominant
 Heterozygous
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 both red
and white 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.
Codominance
A
red flower and a white flower produce
pink flowers. Incomplete
A
black cat and a tan cat produce tabby
cats, cats where black and tan fur is seen
together.
Codominance
Incomplete or Codominance?
A
blue blahblah bird and a white blahblah
bird produce offspring that are silver.
Incomplete
A
certain species of mouse with black fur is
crossed with a mouse with white fur and
all of the offspring have grey fur.
Incomplete
A
woman with blood type A and a man with
blood type B have a child with blood type
AB.
Codominance
Multiple Alleles
 Single
gene with
more than two
alleles.
 example:
type
human blood
Blood Types (codominant)
 Blood
type is
codominant
 IA and IB are
dominant.
 i 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 (many) genes

Polygenic traits often show a
wide range of phenotypes.

example: human skin color employs more than
four different genes
 Skin
color genes: AaBbCcDd
Genes and the Environment

The characteristics of any organism are not
determined solely by the genes that organism
inherits.

Genes provide a plan for development, but
how that plan unfolds also depends on the
environment.

Both nature and nurture
14.1 – Human
Chromosomes
Karyotype
 Chart
of chromosome pairs
arranged by decreasing size.
 Shows unusual number of chromosomes
 Can detect trisomy 21 (Down syndrome)
 Identifies male or female
 Shows genome – full set of
genetic information.
Karyotype
Normal Female
Karyotype
Female with Down Syndrome
Sex Chromosomes
X
and Y chromosomes
 Determine the sex of the offspring
 Females are XX
 Males are XY
Sex Chromosomes
 All
other chromosomes are
autosomes.
 Everyone has 46 chromsomes:
2 sex chromosomes and
44 autosomes.
Sex-linked Traits
 Traits
inherited on X and Y chromosomes.
 Most
are on the X chromosome (because it’s
bigger)
 Example)
Color blindness is a recessive
sex-linked trait on the X-chromosome
 Males
show recessive
sex-linked traits more than females
 Why?
Sex-linked Traits
 Males
get only one X chromosome
Therefore,
males show all 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 carriers
 A woman can have normal vision but
carry the recessive allele 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 body.

Barr bodies are generally not found in males
because their single X chromosome is
still active.
Pedigree Study
 Method
of determining the genotype
of individuals by looking at
inheritance patterns
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—
passes through three generations of a family.

The allele for the white forelock trait is
dominant.
Human Pedigrees

Top of the chart is grandfather with the white
forelock trait.

Two of his three children
inherited the trait.

Three grandchildren have the trait,
but two do not.
Human Pedigrees

Because the white forelock trait is dominant, all
family members lacking this trait must have
homozygous recessive alleles.

One of the grandfather’s children lacks the white
forelock trait, so the grandfather must be
heterozygous for this trait.