Transcript document

DNA – March 23, 2011
1. Name and describe one of the sex-linked
diseases we discussed.
2. The eye color of a fruit fly can be red (R) or
white (r). This is a sex-linked trait.
– Show the cross for a white-eyed male and a
heterozygous female.
– What is the probability that their offspring will
have red eyes? White eyes?
Today’s Objective
• Student will be able to…
– Interpret and create pedigrees
Ms. Klinkhachorn
March 23, 2011
What is a pedigree?
What is a pedigree?
• Visual representation of how traits are passed
on from one generation to the next
Why should we care about pedigrees?
Why should we care about pedigrees?
• To know your family history of genetic
– Example: You can track Sickle-Cell in your family
and figure out who has it
Create a Key!
• Examine the pedigree on the following slide.
• Draw the pedigree on your paper.
• Figure out what the following represent:
– Circle
– Square
– Horizontal line DIRECTLY connecting shapes
– Horizontal line indirectly connecting shapes
– Long vertical line
– Shaded shape
Create a Key
Pedigree Key
Horizontal Line (Direct)
Horizontal Line (Indirect)
Vertical Line
Shaded shape
Generation Difference
Person with the trait
Design a Pedigree
• Draw a pedigree for your IMMEDIATE family
– Your mom and dad and siblings
– Pick one characteristic
HW: Design a Pedigree
• Create a pedigree for a trait in your family.
– Examples: Height, Hair Texture, Hair Color, Eye
• Include (within reason)
– At least 3 generations
– All mating pairs and offspring
– Shading to indicate who has what trait
Design a Pedigree
• Answer the following questions about your
own pedigree:
– How many males are in the family? Females?
– How many members of the family have the trait
your are looking for?
– What is the largest family shown (2 parents +
DNA – March 24, 2011
1. What is a pedigree? Why are these useful for
you to learn about?
2. In a pedigree, what do the following
Direct Horizontal line
Vertical line
Shaded shape
Today’s Objective
– Interpret and create pedigrees
How to Analyze a Pedigree
1. Guess
– Decide if the shaded trait is dominant or recessive
2. Assign
– Write out genotypes based on your guess of
dominant or recessive
3. Check
– Do the answers you put make sense?
4. Readjust
– Only if necessary
Practice Problem 1
• Draw the pedigree
– There are 4 people in the family
– Mom and Dad do not express the trait
– They have 2 children – a boy and a girl
– The girl has the trait we are studying. The boy
does not
Practice Problem 2
• Draw the pedigree
– A couple has 3 children: a girl and 2 boys
– Both parents have the trait we are studying
Practice Problem 3
• Draw the following pedigree
– Family of 3 people
– Dad has the trait and so does his daughter
DNA – March 25, 2011
1. Draw the following pedigree
6 members of the family
Mom and Dad have 2 children: 1 girl and 1 boy
The son is married and has a boy
The daughter shows the trait and so do the wife of
the son and their boy (the grandchild)
2. What trait are we studying (Dominant or
Recessive)? How do you know? Justify your
3. Give genotypes for each member of the family.
4. Fill out your self-eval on the back of your DNA
Dominant Pedigrees
• Every affected individual has at least one
affected parent
• Two affected individuals may have unaffected
Recessive Pedigrees
• An individual who is affected may have
parents who are not affected
• All the children of two affected individuals are
also affected
Sex-Linked Pedigrees
• Will often see a half-shaded shape
– These indicate carriers
Practice Pedigree – Colorblindness
• Draw the pedigree:
– 3 generations, 7 total members
– The grandparents have 3 children: 2 girls and a
– The grandpa is colorblind and so is one of his
daughters and his son
– The son marries a girl and they have a son
• Give the genotypes and then shade anybody
who is a carrier in your pedigree
Scenario 1
One of the bulls is sick with cow disease, which we
know is a sex-linked recessive disease. This bull
mates with a cow that is a carrier for the disease.
1. What are the genotypes of each of the parents?
2. Show the cross.
3. Assume that this cow couple has 4 baby
cows/bulls, each with a different phenotype (as
found in each of the boxes of your Punnett
square). Draw this family’s pedigree.
Scenario 2
A farmer wants to breed a cow and a bull in order to enter
them into the “Best Looking Cow” competition at the state
fair. He mates a heterozygous blue (B) bull with a yellow (Y)
If skin color is an incomplete dominant trait…
1. What is the bull’s genotype? What is the cow’s genotype?
2. Show the cross.
3. Give the phenotypic ratio.
4. How would this ratio change if skin color had been a
codominant trait instead?
Scenario 3
A different cow family is bred on the farm. The
farmer knows the bull is sick, but the cow is
completely healthy for this sex-linked recessive
1.Show the cross.
2.Does this farmer need to worry about having
sick cows? Why/Why not?
Practice Drawing Pedigrees
• Create a pedigree for Cystic Fibrosis, a
recessive disease, based off of the following
– Mom is heterozygous. Dad is sick.
– They have three children – two girls who are
carriers and one boy who is healthy.
– One of the daughters marries a boy who is sick.
• They have two children. The girl is sick. The boy is a