Transcript Mendel Genetics/Genetics Intro

All in the Family
Using Pedigrees to Introduce
Genetic Concepts
Libbie Coleman, Jenn Horton and Heather Parker 2013
Warm Up
1. According to what we learned in
meiosis, why do 2 siblings not look
alike?
2. How many chromosomes do each
parent donate to the final fertilized egg
cell?
3. Homework: problems 1-2 on the
handout.
Pedigree Basics
male
a mating
female
parents
affected male
offspring
affected female
siblings
Albinism
Trait: Albinism
George
Sandra
Daniel
Tom
Alan
Arlene
Sam
Wilma
Ann
Abigail
The Kendrick Family
Michael
Christopher
A. What observations can
you make about the
pedigree?
• There are babies,
men, and women.
• Albinism skips a
generation.
• Red hair in just one
child.
• The siblings don’t look
alike.
B. What questions do you
have about our observations?
•Why does the trait skip a
generation?
•Why don’t all the children
look alike?
•Why do parents who both
have brown eyes, have a
child who has blue eyes?
5th period
• Does the trait go on forever, will it effect
future generations, or will it terminate?
• What is the frequency of this trait
effecting people in this family?
• What is the pattern, what kind of pattern
do traits follow?
6th period
Our driving question:
• Why do traits skip generations?
Model of Inheritance (so far...)
TERMS
gene
trait
RELATIONSHIPS
1. Sexually reproducing organisms
have two genes that determine
each trait, one from each parent.
a. A parent passes only one of his/her
two genes for a trait to each
offspring.
b. Random chance determines which of
the two genes is passed to each
offspring.
A look at some famous data...
Mendel observed the following kinds of
pea plants in his garden:
C. What controls flower color in
these pea plants?
D. Since there are two different colors what does this tell
us about the gene controlling the color trait?
We call these different forms of a gene “alleles”.
We can now add the following to the model:
Model of Inheritance (so far...)
TERMS
gene
trait
alleles
RELATIONSHIPS
1.Sexually reproducing organisms have two genes that
determine each trait, one from each parent.
a. A parent passes only one of his/her two genes for a trait to
each offspring.
b. Random chance determines which of the two genes is passed
to each offspring.
2. Genes for a trait can occur in different forms
called alleles.
Warm Up:
• What did Mendel notice about flower
color?
• What did this tell him about genes?
• What is an allele?
• So for pea flowers, there
are two alleles for color:
purple and white. We will
represent the purple allele
with a P and the white allele
with a p.
P = purple allele
p = white allele
Mendel began by creating lines of plants that
were “pure-breeding” for purple flowers and
“pure-breeding” for white flowers.
E. What do you think “pure-breeding” means?
F. Since we know each plant has two alleles for color, what two alleles do
you think a pure-breeding purple plant has? What two alleles do you
think a pure-breeding white plant has?
Purple:
?
White:
?
?
?
Mendel then crossed (mated) pure-breeding purple flowers
with pure-breeding white flowers. Crossing pure-breeding
individuals with opposite traits is called a “Parental Cross”.
P (parental cross)
F1 generation (offspring
of parental cross)
X
What happened?
All of the offspring
were purple!
G. TERMS
Parental cross: A mating between two
purebreeding individuals with opposite traits.
F1 generation: the offspring of a parental cross.
H. Based on this data, our model, and the alleles of the two
pure-breeding parents, what two alleles do the purple
flowers in the F1 generation have?
P (parental cross)
F1 generation (offspring
of parental cross)
X
We can now add to our model:
Model of Inheritance (so far...)
TERMS
gene
trait
alleles
variation
RELATIONSHIPS
1.Sexually reproducing organisms have two genes that determine
each trait, one from each parent.
a.
b.
A parent passes only one of his/her two genes for a trait to each
offspring.
Random chance determines which of the two genes is passed to each
offspring.
2. Genes for a trait can occur in different forms called
alleles.
3. When there are two variations of a trait in a
population there are two alleles and three
possible combinations of alleles that
individuals can have: PP, Pp, pp
I. There are 3 combinations of alleles but there are only 2
forms of the trait: purple and white. How is this possible?
Model of Inheritance (so far...)
TERMS
gene
trait
alleles
variation
dominant
recessive
RELATIONSHIPS
1.Sexually reproducing organisms have two genes that determine each
trait, one from each parent.
a.
b.
A parent passes only one of his/her two genes for a trait to each offspring.
Random chance determines which of the two genes is passed to each
offspring.
2. Genes for a trait can occur in different forms called alleles.
3. . When there are two variations of a trait in a population there
are two alleles and three possible combinations of alleles that
individuals can have: PP, Pp, pp
a. The dominant form of the trait is a
capital letter PP or Pp and P is called the
dominant allele. We will use capital letters
for the dominant form.
b. the variation of the trait that shows in
pp individuals is the recessive form of the
trait and p is called the recessive allele.
In further experiments Mendel allowed the F1 purple flowers to
self-pollinate.
F1 (1st generation
offspring)
F2 (2nd
generation
offspring)
Both purple and white offspring resulted in the second (F2)
generation - but 3 times more purple than white. In other words,
the ratio of purple to white was 3:1.
TERM: F2 generation - offspring of a cross between two F1
individuals.
J. Using the model, explain how white
flowers came from the two purple F1
parents.
K. Using the model, explain why there are three
times more purple offspring than white.
Now we’re ready to return to the Kendrick
family.
1.
2.
3.
Assign letters to the alleles for albino and normal
pigmentation.
Write in the alleles for each family member. Use a
“?” for alleles of which we cannot be certain.
In the space provided, use the terms and
relationships of the model to answer our driving
question.
DRIVING QUESTION: