Warm- Up
Brown fur (B)is dominant to white fur (b) in a
Type of bunny. Draw a Punnett square to
show a cross between a homozygous
recessive male and a heterozygous female.
1. What genotype(s) in the offspring will
code for brown fur?
2. What is the probability that their bunnies
will have white fur?
What is a Dihybrid Cross?
a. “Di” means two
b. In a dihybrid cross
– Two parents are mated (hybrid)
– We examine two traits (di)
A dihybrid cross is used to determine the
possible offspring of two parents based on
two traits.
c. In this example:
• Tail length is
indicated by S for
short tail or s for
long tail.
• Coat color is
indicated by B for
brown coat or b
for white coat
while
Let’s Try a Problem
▬► Consider this cross
Pea Plants can have these traits
Round (R)
Wrinkled (r)
Yellow (Y)
Green (y)
Steps to solving Dihybrid problems
Copy the Problem
• A pea plant that is heterozygous for
round, yellow seeds is self
fertilized, do a Punnett Square to
solve.
Copy the Steps
Step 1: Determine the parental
genotypes
Heterozygous=
Round= ___ yellow=___seeds
Combine=______________
Step 2: Determine the gametes.
Use FOIL method {First, Outer, Inner, Last}
RrYy
RY, Ry, rY, ry (parent 1) and RY,
Ry, rY, ry (parent 2)
Step 3: Put gametes on Punnett Square
Sex Linked Trait Examples
• Hemophilia A (Factor VIII
deficiency)
• Red/Green color blindness
• Male-pattern baldness*
• Duchenne Muscular Dystrophy
(DMD)
Chromosomes
a. The sex chromosomes are the 23rd
pair of chromosomes.
b. The other 22 pairs of chromosomes
are called autosomes.
c. Traits or diseases can be either sexlinked or autosomal
What are Pedigrees?
a.
Pedigrees
-
-
chart
show how a trait is
passed down over
several
generations
Can show
autosomal or sexlinked traits
b. Pedigrees look like
family trees
Example
What are the Sex chromosomes?
c.
d.
The 23rd pair of chromosomes determine
your sex.
There are two different sex chromosomes: X
and Y
Females have the chromosomes XX
Males have the chromosomes XY
e.
Where do we get the first X chromosome from?
a.
b.
What are Sex-Linked Traits?
a. Certain traits are called sex-linked
because the traits are determined by
genes on the X and Y chromosomes (the
sex chromosomes).
b. Most sex-linked traits are only found on
the X chromosome.
What are the Sex chromosomes?
c. Genetic diseases or mutations are carried on the
X chromosome.
- Females are more likely to be carriers
because they have two X chromosomes
-
Males are more likely to inherit genetic
diseases because they only have one X
chromosome
-
Example: Red/Green Colorblindness occurs in
1 out of 10 males in the US and 1 out of 100
females in the US.
Look at Chromosome Chart
Warm Up
Yellow seed color (Y) is dominant to green seed color
(y), and round seeds (R) are dominant to wrinkled
seeds (r). A plant that is homozygous for green,
wrinkled seeds is crossed with a heterozygous
yellow and round plant. Draw the dihybrid cross.
What’s the probability that they will produce plants with
yellow, wrinkled seeds?
Agenda
• Objectives: SWBAT: Identify the sex
chromosomes in humans and recognize
inheritance patterns that are sex-linked,
using a pedigree or scenario
• Pedigrees
• Complete Practice Sheet
• White Board Practice (If there’s time)
• Exit Ticket
• Gather materials for Quiz
Examine a Pedigree
Pedigree Worksheet
Put together packet
•
•
•
•
•
•
•
•
Phenotype Study
Genetics Review 1
Reading guide 6.3
Punnett Squares- Crosses involving one trait
Bill Nye Video Questions
Punnett Square Worksheet
Human Chromosomes
Bikini Bottom Genetics (I still have those that
were turned in)
Warm Up
1. What’s the phenotype of person #3?
2. What’s the genotype of person # 4?
3. Who are the children of person’s 1 and 2?
Agenda
•
•
•
•
White Board Review
Turn in packets
Quiz
Video
Draw the symbol for carrier female
• In bunnies, brown fur (B) is dominant to white fur
(b) and short fur (S) is dominant to long fur (s).
1. What would be the genotype of a heterozygous
brown bunny with short fur?
2. What about a homozygous white bunny with short
fur?
• If brown fur is dominant to white fur and short fur
is dominant to long fur, what’s the probability that
the offspring will be brown with short fur?
Write the genotype of a male with
hemophilia (which is caused by a
recessive gene on the X chromosome)
A heterozygous tall plant is crossed with
a short plant. The tall gene is dominant
to the short gene in plants. What’s the
probability that the offspring will be tall?
What percent of the offspring are
homozygous recessive?
If the dominant fur color is gray and the
recessive fur color is black, what’s the
probability of the offspring having gray fur?
In certain breeds of dogs, deafness is due
to a recessive allele (d) of a particular gene, and
normal hearing is due to its dominant allele (D).
What percentage of the offspring of a normal
heterozygous (Dd) dog and a deaf dog (dd)
would be expected to have normal hearing?
The following genotypes were found in a male cat and
a female cat: BbSs (male) bbSS (female)
Which one of the following choices is true of the
phenotype of offspring from these parents?
a. All offspring will have black fur.
b. All offspring will have white fur.
c. All offspring will have long-haired fur.
d. All offspring will have short-haired fur.
Hemophilia is a sex-linked recessive
disease. If a woman has a genotype
XRXr does she have hemophilia?
If a man is XrY does he have hemophilia?
A woman is XRXr and a man is XrY, what’s
the probability that their children will have
hemophilia?
A man with a widow’s peak marries a woman with a
straight hairline. Use the letter “H”
• If one of his parents had a widow’s peak and the
other did not, what is his genotype?
• What’s the probability that they will have children
with a widow’s peak?
A pregnant couple wants to know if their child will have curly hair.
Having curly hair is a dominant trait. The mother has the prettiest
curls and so do her parents. The father however, has straight
hair. What’s the probability that their child will have curly hair?
Autosomal or sex-linked disorder?
Autosomal or sex-linked disorder?
Clean up White Boards
• Turn in your markers and white boards
• Spread yourselves out around the classroom for
the quiz
Cracking the code
• http://www.pbs.org/wgbh/nova/body/cracking-thecode-of-life.html
Warm Up
1. What are some traits that can be passed down in
a family?
2. Are all traits inherited the same way? Explain
what you think in complete sentences.
Agenda
• Objectives: SWBAT Define and distinguish
between different modes of inheritance.
• Look at different scenarios of inheritance
• Worksheet
• DNA Cracking the Code Video
Scenario 1
Tay-sachs disease is caused by a recessive gene
on chromosome # 15. If two parents are carriers
for the disease, they have a 25% chance of
having a child with the disease.
Scenario 2
• The lubber grasshopper is black with red and yellow
stripes. Lubber grasshoppers are produced when a
grasshopper with yellow stripes mates with a
grasshopper with red stripes. Red stripes are
expressed with the homozygous dominant (RR)
genotype, yellow stripes with the homozygous (rr)
genotype, and red and yellow stripes with the
heterozygous (Rr) genotype.
Scenario 3
• Suppose you have two rose plants, both
with pink flowers. You cross the two plants
and are surprised to find that, while most of
the offspring have pink flowers, one has red
flowers and another one has white flowers.
Scenario 4
• Queen Victoria's eldest daughter, Victoria,
apparently escaped the hemophilia gene as it did
not appear in any of her descendants. Victoria's
fifth child, Helena may have been a carrier
because two healthy sons survived to adulthood
but two other sons died in infancy and her two
daughters did not have issue. Her son Leopold
suffered from hemophilia and her daughters Alice
and Beatrice were confirmed carriers of the gene.
Scenario 5
• There is a wide range of different eye colors in
humans. Someone can have very dark, almost
black eyes. Another person can have light brown
eyes. There are different shades of blue eyes
person can have, some are bright and some are
more gray. Why is there so much variation?
Exit ticket
• Say the following chart shows a pedigree of
hemophilia within a family. Identify the sex and
whether or not the person has hemophilia
1. Person 1
2. Person 6
3. Person 12