Download Traits and Families

Traits and Families
L. Coleman 2013
modified for MBER 4/15
• We will begin by looking at several families.
Each group will look at a different family that
has a specific trait. You will look for patterns in
the occurrence of that trait that might help us
understand how it might be passed down in
the family.
• Each group will create a pedigree of the family
to help uncover any patterns that might exist.
(A pedigree is just a family tree that shows which
family members have a particular genetic trait.)
Pedigree Basics
male
a mating
female
parents
affected male
offspring
affected female
siblings
deceased
Practice
TRAIT = Red Hair
John and Jane Stevens are married. John has red hair but
Jane is a brunette. Their first child Susan has red hair, but
the second child George is blonde and their youngest, Anne
has brown hair. Susan is married to a dark-haired man
named Ted. Their daughter Eva has dark hair.
Make a pedigree for the Stevens family for the red hair trait.
John
Ted
Susan
Eva
Jane
George
Anne
Patterns in pedigrees:
What patterns do you notice in this family?
Patterns here?
Patterns in this family?
DIRECTIONS:
1. Figure out pedigree on whiteboard first.
2. Identify all family members on the pedigree by name.
3. Once you have it competed, transfer the pedigree to
poster paper.
a. At the top of the paper write:
1) the name of the family.
2) The name of the trait.
3) The # of variations of the trait and what they are.
b. At the bottom, write:
1) PATTERNS: list any patterns you noticed in the
occurrence of the trait in the family.
2) QUESTIONS: list any questions you have (at
LEAST one question required).
Write Period and Table # somewhere on the front.
Learn about 2 other families.
• A and B partners rotate to the next table. C
and D partners stay to teach other groups
about your family.
– “Teachers”, explain what the trait is and what
symptoms it causes.
• Tell how many variations of the trait are in the family and
what they are.
• Point out any patterns you identified.
– “Learners”, feel free to ask questions. Write down
what you learn at each table.
• Then we will reverse roles.
What did you observe in
looking at all these families and
their traits?
• Is there just one pattern? Just one way
that traits are passed down in families?
• What are some of the differences you
noticed between the 3 families you
observed?
• Do we have all the ideas we need to
explain all the different patterns?
Model of Inheritance (so far...)
TERMS
gene
trait
allele
Add to glossary:
ALLELES: different
versions of genes for the
same trait (example: for
eye color there are blue
and brown alleles).
RELATIONSHIPS
1. Sexually reproducing organisms
have two genes that determine
each trait (inherited
characteristic), 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 versions called alleles.
We will start by looking at the most famous genetics data ever gathered...
Gregor Mendel’s Experiments with Pea Plants
(published 1865)
Gregor Mendel was a priest in what is now the
Czech Republic. He was a high school science teacher
and keeper of the monastery garden.
His curiosity about heredity led him do numerous
experiments on pea plants. His results and conclusions
written in 1865 are the foundation of modern genetics.
Mendel’s monastery today.
Mendel’s garden.
He chose pea plants because of
the structure of their flowers. Male
and female reproductive parts are
enclosed by petals.
He saw that this would allow him
to control the parent plants in a
cross.
He meticulously clipped off the stamens
of a plant’s flowers to prevent selfpollination…
He tested more than 70,000
pea plants!!
… then with a small brush moved
pollen from the stamen of the desired
parent to the stigma of the first plant.
Pea plants have many traits that Mendel
could have chosen to study.
• Just like the families we studied, he observed
many different patterns in the occurrence of
the various traits.
• But, he decided the best way to uncover what
was going on was to begin with the simplest
case.
• So, he decided to focus on traits that
occurred in just two distinct variations.
One of those was flower color. Mendel observed
that there were only two colors of flower in his pea
plants: either white or purple.
Mendel didn’t know about alleles at first but we do. So how
many versions (alleles) of the color gene do you think
there are in pea plants?
•Yes, there are two alleles
for color: purple and white.
We will represent the purple
allele with a 1 and the white
allele with a 2.
1 = purple allele
2 = white allele
Mendel began by creating lines of plants that
were pure-breeding for purple flowers and
pure-breeding for white flowers.
What do you think “pure-breeding” means?
A. Our model says 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? (Remember 1= purple allele,
2 = white allele)
Purple:
?
White:
?
?
?
Mendel then crossed (symbolize by “X”) pure-breeding purple
flowers with pure-breeding white flowers. He called this a
“Parental Cross” (“P”) and he called their offspring the “F1”
generation (from Latin “Filia”, meaning daughter).
X
P
(parental cross)
F1
What do you think
happened in the F1
generation?
(offspring of parental cross)
All of the F1 offspring
were purple!
B. 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
X
F1
1,1
2,2
?
1,2
C. So, when there are two alleles for a
trait (1 & 2 in this case), how many
different combinations of alleles are
possible for individuals to have?
What are they?
There are three:
1,1
2,2 and 1,2
We can now add to our 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.
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.
phenotype
genotype 3. When there are two variations of a trait
(phenotypes) in a population, there are two alleles
(1 & 2) and three possible combinations
(genotypes) individuals can have: (1,1) or (2,2) or
(1,2).
Add to glossary:
• PHENOTYPE: the variation of a trait that shows in an individual.
Examples: purple flowers, blue eyes
• GENOTYPE: the combination of alleles that an individual has.
Examples: (1,1) (2,2) (1,2)
D. There are 3 combinations of alleles (genotypes): 1,1
and 2,2 and 1,2.
But there are only 2 variations of the trait (phenotypes):
purple and white.
What do you think might explain this?
PURE-BREEDING
PURPLE PARENT
(1,1)
PURE-BREEDING
WHITE PARENT
X
(2,2)
F1 OFFSPRING
PURPLE
(1,2)
Model of Inheritance (so far...)
TERMS
gene
trait
alleles
phenotype
genotype
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 (phenotypes) in a
population then there are two alleles (1 and 2) and three
possible combinations of alleles (genotypes) that individuals
can have: (1,1) or (2,2) or (1,2).
a. If (1,1) and (1,2) have one phenotype and
(2,2) has the other, then 1 is the dominant
allele. It always shows when present.
b. 2 is the recessive allele. It only shows if no
dominant allele is present.
In further experiments Mendel allowed the F1 purple flowers to
self-pollinate.
F1
What do you think
happened?
F2
(2nd generation
offspring)
E. Using the model, predict whether or not it is
possible for these parents to have white offspring.
Both purple and white offspring resulted - but 3 times more
purple than white. In other words, the ratio of purple to white
was 3:1.
F. Explain why there are three times
more purple offspring than white.
Mendel did the same experiments with several other traits in
pea plants. All produced the same result:
One variation of the trait disappeared in the 1st generation
then reappeared in the 2nd. The ratio was always 3:1.
2nd generation data for various traits:
Add to glossaries:
• Homozygous: a genotype in which the
two alleles are the same. (pure-breeding)
– Examples: (1,1) and (2,2)
• Heterozygous: a genotype in which the
two alleles are different.
– Example: (1,2)
Let’s look at a family to see if we can
apply the model and explain the
patterns we see.
ALBINISM is a rare genetic trait found in many species.
Organisms with albinism are unable to produce pigment
proteins. In animals the protein affected is melanin, in plants
it is chlorophyll.
George
Sandra
Daniel
Tom
Alan
Arlene
Sam
Wilma
Ann
Michael
Abigail
The Kendrick Family
Christopher
Trait: Albinism
Can you use Mendel’s model to explain the
inheritance of albinism in the Kendrick family?
1. What are the variations (phenotypes) of this trait?
2. What are the alleles? Assign numbers to the alleles.
3. Study the pattern. Which allele do you think is dominant
and which is recessive?
4. What are the possible genotypes and which phenotype
goes with each one?
5. Now, go to the pedigree and fill in the genotypes (as
much as you can know for sure) of each member of the
family.
6. Be able to use your analysis of the pedigree and
Mendel’s model to explain in words the pattern of
occurrence of this trait in the Kendrick family.
George
Sandra
Daniel
Tom
Alan
Arlene
Sam
Wilma
Ann
Abigail
Michael
Christopher
KEY
Alleles:
1=normal
2=albino
Genotypes & Phenotypes:
1,1
normal
1,2
2,2 = albino
1,_
Sandra
George
1,_
2,2
1,2
1,2
1,2
Tom
Sam
Wilma
Arlene
1,2
1,2
Ann
Michael
1,_
1,_
1,_
Daniel
Alan
Abigail
The Kendrick Family
2,2
Christopher
Trait: Albinism
Mendel figured out 3 REALLY IMPORTANT
things that no one before him had discovered.
He called them “Laws of Inheritance”
1st Law: We have two genes (he called them
“factors”) for each trait. A parent gives just one of
them to each child - which one is determined by
random chance.
2nd Law: Law of dominance. Some versions of
genes are dominant to others.
3rd Law: Traits are inherited independently of one
another (so each is a separate random chance
event).
Model of Inheritance (so far...)
TERMS
gene
trait 1st law
alleles
phenotype
genotype
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 (phenotypes) in a
population then there are two alleles (1 and 2) and three
possible combinations of alleles (genotypes) that individuals
can have: (1,1) or (2,2) or (1,2).
a. If (1,1) and (1,2) have one phenotype and (2,2) has
2nd law
the other, then 1 is the dominant allele. It always
shows when present.
b. 2 is the recessive allele. It only shows if no dominant
allele is present.
3rd law
4. Traits are USUALLY inherited independently of one
another.
Now that we have Mendel’s model, let’s take a
trip “into the wild” (nature!). You will collect
organisms (dragonbugs) in their natural habitat,
mate them, then observe the traits of their
offspring.
To get to the assigned problems, first
open folder “Coleman Genetics” on
the desktop.
THEN:
VGLII-3.2.1.A
OPEN WORK *
Coleman Genetics
Mendel VGL problems
Long short legs
1. Phenotypes and genders of individuals you collected in the wild
will appear:
Trait:
Phenotypes:
Click here
to view the
phenotype
2. Click on the male and female you want to cross, then click “CROSS”
on the menu. A “cage” showing offspring appears.
3. Choose next cross. May be from original field population or
offspring cage.
To close a problem:
1. Close each cage. Select “YES” in the box that opens.
2. Click on the “Save Work” folder
3. “Do you wish to save?”. Select
NO.
Now you will be able to open the next problem.
To get to the assigned problems, first
open folder “Coleman Genetics” on
the desktop.
THEN:
VGLII-3.2.1.A
OPEN WORK *
Coleman Genetics
Mendel VGL problems
A. bent zigzag antenna
B. blue brown wings
1. Phenotypes and genders of individuals you collected in the wild
will appear:
Trait:
Phenotypes:
Click here
to view the
phenotype
2. Click on the male and female you want to cross, then click “CROSS”
on the menu. A “cage” showing offspring appears.
3. Choose next cross. May be from original field population or any
offspring cage.
Back to your families…
Now that we have a model to explain how traits are passed
down, let’s go back and look at your original families and
pedigrees. Be prepared to share with the class.
1.Compare the pattern of inheritance in your family to Mendel’s
model.
2.Can you fully explain the pattern using Mendel’s model?
a) If yes:
1) Identify the alleles for the trait and assign symbols to them
(use the 1,2 system where 1= dominant allele).
2) Figure out as much as you can about the genotypes of the
family members. Write these on your poster.
b) If no:
1) How is the pattern in your family different from Mendel’s
model? Write your thoughts on your poster.
2) Look carefully at your pocket Mendel. Try to think of a
statement or statements we could add to the model so that it
would include your family. It might help you to start with
something like “In some cases…”
Analyzing the VGL data:
1. What are the phenotypes?
2. What are the alleles?
3. What are the possible
genotypes?
4. Does it fit Mendel’s model?
5. If not, how is it different and
how might you explain it?
6. What statement could we add
to the model to explain this
pattern?
PERIOD 4
Analyzing the VGL data:
1. What are the phenotypes?
2. What are the alleles?
3. What are the possible
genotypes?
4. Does it fit Mendel’s model?
5. If not, how is it different and
how might you explain it?
6. What statement could we
add to the model to explain
this pattern?
7. What could we call this
pattern?
Extension to Model
TERMS
Codominance/
Incomplete dominance
RELATIONSHIPS
5. When there are three variations
of a trait and two alleles, each
genotype [(1,1), (1,2), (2,2)] has a
different phenotype. BOTH 1 and
2 are expressed so neither is
dominant. They are codominant
(or show incomplete
dominance).
Return to the Marcus family
and Achondroplasia
• All groups concluded that:
– there are 3 variations of the trait
(phenotoypes).
– each genotype has its own phenotype.
• Now we know that this is an example of
codominance.
1 = achondroplasia
2 = normal
(1,1) = Severe (lethal) Achondroplasia
(1,2) = Achondroplasia
(2,2) = Normal
What is behind the 3 phenotypes for achondroplasia?
REVIEW: What does a gene code for? How are genes used in/by cells?
A gene is a recipe for a protein. It is used by the cell to make
that protein.
In achondroplasia, the normal allele (FGRF3) codes for a
protein (fibroblast growth factor) that is part of the structure of
normal bones, including those of the arms and legs. The
achondroplasia allele produces a protein that no longer functions
correctly, resulting in disrupted, abnormal bone growth.
What could happen to a gene that would result in an abnormal
protein?
If there is a mutation, does it get passed down from parents to
offspring? Explain.
So how did we get two different forms of this gene in this case? In
other words, where do alleles for a trait come from?
MUTATIONS are the original source of alleles.
Consider the function of the FGFR3 gene. Form a
hypothesis to explain why there is a difference in severity
between individuals who have one achondroplasia allele
and those who have two achondroplasia alleles.
FGFR3 gene
mutation
1
1
Severe (lethal)
achondroplasia
1
2
Achondroplasia
2
2
Normal phenotype
The PAH gene codes for an enzyme (phenylalanine hydroxylase) needed to break down the
amino acid phenylalanine in the body. In PKU, a mutation in the PAH gene makes it unable to
produce a properly functioning enzyme. As a result, phenylalanine builds up in the
bloodstream of people with PKU, causing brain damage and cognitive deficits.
Our PKU groups found:
the normal allele is
dominant, the PKU
allele is recessive, and
it fits Mendel’s model.
1 = normal
2 = PKU
1,1
normal
1,2
2,2 = PKU
Why do you think a
heterozygote is still able to
function normally? Why do
you think the pattern in PKU
is different from
achondroplasia?
mutation
PAH
1
1
Normal
1
2
Normal
2
2
Has PKU
PKU affects an enzyme.
Achondroplasia affects a structural protein.
ENZYMES:
• Make all chemical
reactions and processes
happen in cells.
• Can be used over and
over because they are
not used up or changed
in reactions.
STRUCTURAL PROTEINS:
• Building materials that
make up structures of the
body (muscles, bones,
organs, blood cells etc.).
“Coleman Genetics” THEN:
VGLII-3.2.1.A
OPEN WORK *
Coleman Genetics
Like DMD.wr2
To close a problem:
1. Close each cage. Select “YES” in the box that opens.
2. Click on the “Save Work” folder
3. “Do you wish to save?”. Select NO.
Gene for achondroplasia
•
•
•
•
What are homologous pairs? What do you notice about them?
Why do we have 2 of each kind of chromosome?
What is on the chromosomes? Genes (alleles) for traits!!
Our Mendel model says we have 2 alleles for each trait.
Why? Where did we get them???
O.I. allele
from mom
2364 genes
from mom
O.I. allele
from dad
2364 genes
from dad
All chromosome #11’s
have 2364 genes.
All chromosome #17’s
have 2010 genes.
X from mom
(2000 genes)
X from dad
X from mom
(2000 genes)
(2000genes)
Our model says there are 2
genes controlling each trait.
Do traits whose genes are
located on the X chromosome
fit our model in all cases?
Y from dad
(72 genes)
Now back to the Medeiros family.
• Trait: Duchenne’s
Muscular Distrophy
• Patterns:
– Kids have it even when
neither parent has it.
– Only males in the family
have it.
How might the way sex is determined
make it more likely for males to show
certain recessive traits than females?
• Read the handout “Chromosomes
and Sex Determination in Humans”.
• Then, brainstorm possible answers to
this question on your whiteboards.
• Be prepared to share your ideas.
“Coleman Genetics” THEN:
VGLII-3.2.1.A
OPEN WORK *
Coleman Genetics
Like DMD.wr2
To close a problem:
1. Close each cage. Select “YES” in the
box that opens.
2. Click on the “Save Work” folder
3. “Do you wish to save?”.
Select NO.
Inheritance of sex in dragonbugs is similar to that of
humans, so now that you have some data about
inheritance of antenna color…
Make your claim:
– What are the alleles?
– Which is dominant?
– How can you explain the different results
for the males and females?
In the “evidence to support your claim”
space: make punnett squares for the key
crosses and explain how they support your
claims.
2364
genes
from
mom
O.I.
allele
from
mom
2364
genes
from
dad
All chromosome
#11’s
have 2364
O.I.
allele
from
dad
All chromosome
#17’s
have 2010
normal
allele
X from
mom
(2000
genes)
DMD
allele
X from
dad
(2000
genes)
X from
mom
(2000
genes)
Y from
dad (72
genes)
Our model says we have 2 genes controlling each
trait. Does our model hold true for traits located
Extension to Model
TERMS
Codominance/
Incomplete dominance
Sex-linked trait
RELATIONSHIPS
5. When there are three variations of a trait and
two alleles, each genotype [(1,1), (1,2), (2,2)]
has a different phenotype. BOTH 1 and 2 are
expressed so neither is dominant. They are
codominant (or show incomplete
dominance).
6. Males receive only one allele for traits on
the unmatched part of the X chromosome so
that allele alone determines their phenotype,
even if it is recessive. Such traits are said to
be sex-linked.
Spectrum with
normal color vision…
and as it
appears with redgreen colorblindness.
R-G colorblind
Normal
Normal
R-G colorblind
Take the test…what do you see?
This is what the test looks like to a
person who is red-green colorblind.
We symbolize the genotypes
differently but work problems the
same as for any other trait:
Sample problem:
•
A woman heterozygous for colorblindness
(a “carrier”) marries a man with normal
color vision. If they have a son, what is the
probability he will be colorblind?
4. Punnett Square:
1. Alleles: 1 = normal
1
2
2 =colorblind
2. Possible genotypes and phenotypes:
1
1,1
Normal
female
1,2
Carrier
female
1,1 = normal 1Y = normal
1,2 = normal 2Y = colorblind
2,2 = colorblind
Y
1Y
Normal
male
2Y
Color
blind
male
3. Show the cross:
heterozygous female x normal male
1,2
x
1,Y
Number of colorblind sons = 1
Total # of sons = 2
Probability son will be colorblind = 1/2.
X1 = brown
X2 = purple
X1X1 = brown
X1X2= brown
X2X2= purple
X1Y = brown
X2Y = purple
Why are sex-linked traits more rare in
females?
• Example: colorblindness
• 1/100 X chromosomes carry colorblind
allele.
– Males get just one X so chance is 1/100 it
will have the allele and they’ll be colorblind.
– Females get two X’s and both must have
the allele so:
• 1/100 x 1/100 = 1/10,000 chance.
Colorblindness occurs in about 1/10,000 females, but DMD
never is seen in females. Why?
Prince Albert
Victoria
Alice
Alfred
Helena
1
9
10
11
Queen Victoria
12
Louise Leopold
2
13
3
14
15
16
Beatrice
Arthur
4
5
6
17
18
19
7
20
8
21
Edward VII
George V
George VI
SPANISH ROYALTY
Queen Elizabeth II
22
23
24
25
26 27
28
GERMAN ROYALTY
29 30 31 32 33
RUSSIAN ROYALTY
(Romanovs)
Hemophilia
in descendants of Queen Victoria
Prince Albert
Victoria
Alice
Alfred
Helena
1
9
10
11
Queen Victoria
12
Louise Leopold
2
13
3
14
15
16
Beatrice
Arthur
4
5
6
17
18
19
7
20
8
21
Edward VII
George V
George VI
SPANISH ROYALTY
Queen Elizabeth II
22
23
24
25
26 27
28
GERMAN ROYALTY
29 30 31 32 33
RUSSIAN ROYALTY
(Romanovs)
Hemophilia
in descendants of Queen Victoria
The McCann family: Inheritance of blood type.
1. Study the McCann family pedigree and look for patterns.
2. Do you see anything that does NOT fit our model so far
(Mendel and the additions we have made to Mendel)? If so,
how is this family different?
3. See if you can figure out from the information on the pedigree
how blood type is inherited.
a.
b.
c.
What are the alleles? How do the alleles interact with each other (is
there dominance, recessiveness, codominance, etc.)?
What are the possible genotypes and corresponding phenotypes?
What are the genotypes of the people on the pedigree?
4. If you would like to test a hypothesis or get additional
information: the envelopes at your table contain more
information about the youngest generation – namely, the blood
types of the people they married when they grew up and the blood
types of their children.
1.
We know that a gene codes for…what?
2.
So with regard to blood type, what do you think A and B might be?
A protein!
– “A” is a protein found on the surface of some people’s red blood cells.
– “B” is a different protein found on the surface of some people’s red blood
cells.
a. What do you think people with blood type
O have?
Explain in your own words why we say that A and B are
b.
3.
4.
AB have?
What do you think people with type
codominant.
Explain in your own words why the O allele is recessive. Why do you
only get type O blood if no A or B allele is present?
Rh is yet another protein that some people have on
their red blood cells and some people don’t. Those who
have it are Rh+ and those who don’t are Rh-.
Which allele do you think is dominant?
Why?
Extending the Model (McCann family)
A
B
B
O
Sue
Jay
Karen
Walter
?
AB
A
B
O
A
Will
Laura
Carol
Tim
Donna
Tony
B
AB
O
AB
A
Ron
Rose
Grace
Beth
Jerry
A
Ryan
Extending the Model (McCann family)
A
BO
Sue
Jay
BO
OO
Karen
Walter
Could be
any type
but O
?
AB
Will
Laura
B
AB
Ron
Rose
BO
AO
Carol
OO
Grace
Tim
AB
Beth
OO
A
Donna
AO
Jerry
Tony
AO
Ryan
Extension to Model
TERMS
Incomplete dominance/
Codominance
Sex-linked
Multiple alleles
RELATIONSHIPS
6. Males receive only one allele for
traits on the unmatched part of the
X chromosome so that allele alone
determines their phenotype, even if
it is recessive. Such traits are said
to be sex-linked.
7. There can be more than 2 alleles
for a trait aka multiple alleles. This
can result in more than three
phenotypes. The alleles can be
dominant/recessive or codominant.