Warm Up: For these Guinea pigs, tan hair is
dominant over black.
• 1. What are the genotypes for each
individual?
• 2. Who is homozygous and who is
heterozygous?
• -----------------------------
•
•
•
•
Dad
Mom
tt
Tt
tt
What are the alleles?
What are the genotypes/phenotypes?
Baby
Where did the ALL alleles come from?
Predict the likelihood that this genotype/ phenotype
would result.
Key Ideas
• How can a Punnett square be used in genetics?
• How can mathematical probability be used in genetics?
Objectives: Using Mendelian
Genetics
• Describe how a Punnett square is used in
genetics.
• List ways to express mathematical probability in
genetics.
Vocabulary
• Punnett square
• Probability
• Pedigree
• Genetic disorder
What You Should Recall.
We’re looking at this…
• You know that Mendel gave us two important laws.
• Independent assortment: Speaks to the fact that genes separate
independent of one another
• Segregation: Speaks to the fact that alleles of the same gene have equal
probability of segregating into gametes.
• Once the gametes are formed, “Mendelian genetics” also gives us
an outline on how to figure out what the likelihood, the
probability, of an offspring has to show particular traits, based
upon dominant & recessive alleles.
• Today you will learn how to figure out the probability of certain
traits being inherited and shown, using Punnett Squares.
Using Punnett Squares
• How can you predict the chances an offspring will have a
certain genotype, therefore phenotype?
• A Punnett square is a model that predicts the probability of
likely outcomes of a genetic cross.
• Remember that a cross is “to mate or breed two individuals.”
• A Punnett square shows all of the genotypes that could result
from a given hybrid cross.
• The important thing to remember is that this shows what could
happen…not necessarily what always happens.
• The simplest Punnett square consists of a square divided into
four boxes.
• This is a monohybrid cross…
• The combination of letters in each box represents one
possible genotype in the offspring.
Meiosis
EVERY CHILD
BORN WOULD
HAVE THE SAME
CHANCES TO
INHERIT ANY OF
THE
COMBINATIONS
OF ALLELES!
Fertilization
Meiosis
Probable
zygotes
that can be
produced
by one
fertilization
Using Punnett Squares
Constructing a Simple Punnett
square for Monohybrid
Crosses
1.
2.
3.
Draw a 2 x 2 chart.
Conclude what the genotype of
the parents’ gametes are based
upon the description given.
Write the GENOTYPE of the
parents’ gametes on the top and
sides of the chart. There is one
letter per column & row.
This represents the allele being
donated by a gamete during
fertilization.
4.
Fill in the columns and rows
corresponding with the heading
allele.
Y
y
y
Y
Yy
Yy
These
are the
possible allele
combinations
for
Yythe offspring
Yy
Ratios and Punnett Squares
• A Punnett square basically predicts: ..
• all the possible combinations for alleles for each trait examined.
• This can be use to predict the likelihood of traits of an offspring… the
probability of things happening.
• It also reveals the ratio of one type of offspring compared to the
other types offspring.
• The ratio can help compare genotypes to other genotypes or
phenotypes to other phenotypes.
• It ultimately shows how the possible offspring compare to the
other offspring.
Ratio Review
• What is a ratio?
• A ratio is an expression, of at least two numbers, that is used
to compare values.
• It is written separated by a colon.
• Ex. If there are (normally) 5 fingers for every hand would be
written as 5:1 ratio of fingers to hands.
• It would be said as “a ratio of 5 fingers to one hand”
• A ratio shows how many events happen compared to the
events of others.
Ratios of Fingers to Hands
• There is a ratio of five fingers to
every one hand.
• Written: 5:1
1
2 3 4
5
1
Using Punnett Squares
• Punnett squares give us genotypes
probabilities to determine
phenotypes.
• In a monohybrid homozygous
dominant cross, all of the
offspring will be homozygous.
• The ratio of the genotypes will be
1 YY:0 [others], meaning all the
offspring will be the same
genotype for the alleles.
• This is called the genotypic ratio.
• The phenotypic ratio describes the
comparison of all the traits
displayed.
• The phenotypic ratio here is all the
dominant form… all dominant.
Y
Y YY
Y
YY
Y YY
YY
Using Punnett Squares
• In a monohybrid cross between a
homozygous dominant and a
homozygous recessive all the
offspring will be heterozygous (ex.
Yy).
• What are the genotypic & phenotypic
ratios here?
• The genotypic ratio would again be
• 1Yy:0 [others].
• Because there is no other alternative,
there is no other thing to compare to.
• Since there’s only 1 genotype, there
can be only 1 phenotype.
• As such, the phenotypes would be all
the dominant form.
Y
y Yy
Y
Yy
y Yy
Yy
Using Punnett Squares
• In a monohybrid
heterozygous cross the
genotypic ratio will be
1 YY : 2 Yy : 1 yy.
• This is what Mendel
observed in his F2
generations!
• What is the phenotypic
ratio?
Y
Y YY
y
Yy
y Yy
yy
• 3 yellow (dominant): 1 green (recessive)
Using Punnett Squares
• Phenotypes
• Remember, genotype determines phenotype, but the
ratio is not always the same between the two.
• You need to think about the trait that will be shown
depending upon the allele combination.
• In a monohybrid cross between homozygotes all the
offspring will be the same, therefore all the offspring will
express the same trait.
• However, in a monohybrid heterozygote
cross, where the genotypic ratio is 1 : 2 : 1,
• the phenotypic ratio will be 3 : 1.
Punnett Squares
Dihybrid Crosses
Mendel noticed that alleles for one gene do not affect the
inheritance of the alleles for another gene.
= independent assortment
• This makes
predicting the
probability of
inheriting a
combination of two
non-linked genes
more challenging
but entirely
possible.
• What does nonlinked mean?
Dihybrid Crosses.
• In order to accomplish this you must consider all possible
gametes for an individual, then perform the cross.
• Let’s try crossing two heterozygotes for pea color and
flower color.
• PpYy x PpYy
• Take a minute and figure out the possible gametes.
Dihybrid Crosses.
• In order to accomplish this you must consider all possible
gametes for an individual, then perform the cross.
• Let’s try crossing two heterozygotes for pea color and
flower color.
• PpYy x PpYy
• Take a minute and figure out the possible gametes.
PY
Dihybrid Crosses.
• In order to accomplish this you must consider all possible
gametes for an individual, then perform the cross.
• Let’s try crossing two heterozygotes for pea color and
flower color.
• PpYy x PpYy
• Take a minute and figure out the possible gametes.
PY pY
Dihybrid Crosses.
• In order to accomplish this you must consider all possible
gametes for an individual, then perform the cross.
• Let’s try crossing two heterozygotes for pea color and
flower color.
• PpYy x PpYy
• Take a minute and figure out the possible gametes.
PY pY Py
Dihybrid Crosses.
• In order to accomplish this you must consider all possible
gametes for an individual, then perform the cross.
• Let’s try crossing two heterozygotes for pea color and
flower color.
• PpYy x PpYy
• Take a minute and figure out the possible gametes.
PY pY Py py
Dihybrid Crosses.
• In order to accomplish this you must consider all possible
gametes for an individual, then perform the cross.
• Let’s try crossing two heterozygotes for pea color and
flower color.
• PpYy x PpYy… Conduct the cross, calculate
probabilities.
PY
PY
pY
Py
py
pY
Py
py
CW/HW
• Complete both sides of the worksheet by next class (25pts).
We will develop this and work on trihybrid crosses tomorrow.
• Questions on HW.
• Answers, then trihybrid.
Trihybrid Crosses
• We have over 30,000 genes.
• Not all of them are “Mendelian” but many are.
• How would you predict the chances an individual inherited this
combination of Mendelian traits from two heterozygotes:
•
•
•
•
•
•
Cleft chin (d)
No dimples (r)
A widows peak (d)
Attached ear lobes (r)
Hitchhikers thumbs (r)
& freckles? (d)
.75
.75x.25
.75x.25x.75
.75x.25x.75x.25
.75x.25x.75x.25x.25
.75x.25x.75x.25x.25x.75 = 0.66% (7 out of 1000)
• The more variables you consider the higher the degree of difficulty
is inherent.
• We’ll stop at three different, non-linked genes but considering
these will help you appreciate just how unique you are!
• The probabilities of another person inheriting the exact same
combination of alleles you did is nearly impossible.
Trihybrid Crosses
• Consider crossing heterozygotes for flower color, pea color,
& pea shape.
• PpYyRr x PpYyRr
• What should you do?
• First identify all the gametes that could form from each
parent (independent assortment & segregation assumed).
• PYR – PYr – PyR – Pyr – pYR – pYr – pyR – pyr
• Then set up your 8 x 8 grid and distribute the
gametes.
2nd: Distribute gametes
PYR – PYr – PyR – Pyr – pYR – pYr – pyR – pyr
PYR PYr
PYR
PYr
PyR
Pyr
pYR
pYr
pyR
pyr
PyR Pyr
pYR pYr
pyR pyr
Combine gametes and analyze.
What is the:
- Genotypic ratio? Phenotypic ratio?
PYR PYr
PyR Pyr
pYR pYr
pyR pyr
PYR
PPYYRR
PPYYRr
PPYyRR
PPYyRr
PpYYRR
PpYYRr
PpYyRR
PpYyRr
PYr
PPYYRr
PPYYrr
PPYyRr
PPYyrr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
PyR
PPYyRR
PPYyRr
PPyyRR
PPyyRr
PpYyRR
PpYyRr
PpyyRR
PpyyRr
Pyr
PPYyRr
PPYyrr
PPyyRr
PPyyrr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
pYR
PpYYRR
PpYYRr
PpYyRR
PpYyRr
ppYYRR
ppYYRr
ppYyRR
ppYyRr
pYr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
ppYYRr
ppYYrr
ppYyRr
ppYyrr
pyR
PpYyRR
PpYyRr
PpyyRR
PpyyRr
ppYyRR
ppYyRr
ppyyRR
ppyyRr
pyr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
ppYyRr
ppYyrr
ppyyRr
ppyyrr
What is the:
- Genotypic ratio? Phenotypic ratio?
GR=1PPYYRR:2PPYYRr:2PPYyRR:1PPYYrr:4PPYyRr:2PPYyrr:1PPyyRR:2PPyyRr:1PPyyrr:
2PpYYRR:4PpYYRr:2PpYYrr:4PpYyRR:8PpYyRr:4PpYyrr:2PpyyRR:4PpyyRr:2Ppyyrr:1ppYYRR:
2ppYYRr: 1ppYYrr:2ppYyRR:4ppYyRr:2ppYyrr:1ppyyRR:2ppyyRr:1ppyyrr
PR=27PYR:9PYw:9PgR:3Pgw:9wYR:3wgR:3wYw:1wgw
PYR PYr
PyR Pyr
pYR pYr
pyR pyr
PYR
PPYYRR
PPYYRr
PPYyRR
PPYyRr
PpYYRR
PpYYRr
PpYyRR
PpYyRr
PYr
PPYYRr
PPYYrr
PPYyRr
PPYyrr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
PyR
PPYyRR
PPYyRr
PPyyRR
PPyyRr
PpYyRR
PpYyRr
PpyyRR
PpyyRr
Pyr
PPYyRr
PPYyrr
PPyyRr
PPyyrr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
pYR
PpYYRR
PpYYRr
PpYyRR
PpYyRr
ppYYRR
ppYYRr
ppYyRR
ppYyRr
pYr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
ppYYRr
ppYYrr
ppYyRr
ppYyrr
pyR
PpYyRR
PpYyRr
PpyyRR
PpyyRr
ppYyRR
ppYyRr
ppyyRR
ppyyRr
pyr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
ppYyRr
ppYyrr
ppyyRr
ppyyrr
How many (out of 64) will be:
- Purple flowers, Yellow peas, Round peas?
What is the:
- Genotypic ratio?
- Phenotypic ratio?
1PPYYRR:2PPYYRr:2PPYyRR:1PPYYrr:4PPYyRr:2PPYyrr:1PPyyRR:
2PPyyRr:1PPyyrr:2PpYYRR:4PpYYRr:2PpYYrr:4PpYyRR:8PpYyRr:
4PpYyrr:2PpyyRR:4PpyyRr:2Ppyyrr:1ppYYRR:2ppYYRr:
1ppYYrr:2ppYyRR:4ppYyRr:2ppYyrr:1ppyyRR:2ppyyRr:1ppyyrr
27PYR:9PYw:9PgR:3Pgw:9wYR:3wgR:3wYw:1wgw
-
white flowers, green peas, wrinkled peas?
Purple flowers, green peas, Round peas?
white flowers, Yellow peas, Round peas?
Purple flowers, green peas, wrinkled peas?
Heterozygous for all three traits?
27 of 64
PYR PYr
PyR Pyr
pYR pYr
pyR pyr
PYR
PPYYRR
PPYYRr
PPYyRR
PPYyRr
PpYYRR
PpYYRr
PpYyRR
PpYyRr
PYr
PPYYRr
PPYYrr
PPYyRr
PPYyrr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
PyR
PPYyRR
PPYyRr
PPyyRR
PPyyRr
PpYyRR
PpYyRr
PpyyRR
PpyyRr
Pyr
PPYyRr
PPYyrr
PPyyRr
PPyyrr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
pYR
PpYYRR
PpYYRr
PpYyRR
PpYyRr
ppYYRR
ppYYRr
ppYyRR
ppYyRr
pYr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
ppYYRr
ppYYrr
ppYyRr
ppYyrr
pyR
PpYyRR
PpYyRr
PpyyRR
PpyyRr
ppYyRR
ppYyRr
ppyyRR
ppyyRr
pyr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
ppYyRr
ppYyrr
ppyyRr
ppyyrr
How many (out of 64) will be:
What is the:
- Genotypic ratio?
- Phenotypic ratio?
1PPYYRR:2PPYYRr:2PPYyRR:1PPYYrr:4PPYyRr:2PPYyrr:1PPyyRR:
2PPyyRr:1PPyyrr:2PpYYRR:4PpYYRr:2PpYYrr:4PpYyRR:8PpYyRr:
4PpYyrr:2PpyyRR:4PpyyRr:2Ppyyrr:1ppYYRR:2ppYYRr:
1ppYYrr:2ppYyRR:4ppYyRr:2ppYyrr:1ppyyRR:2ppyyRr:1ppyyrr
27PYR:9PYw:9PgR:3Pgw:9wYR:3wgR:3wYw:1wgw
-
Purple flowers, Yellow peas, Round peas?
-
white flowers, green peas, wrinkled peas?
-
Purple flowers, green peas, Round peas?
white flowers, Yellow peas, Round peas?
Purple flowers, green peas, wrinkled peas?
Heterozygous for all three traits?
1 of 64
PYR PYr
PyR Pyr
pYR pYr
pyR pyr
PYR
PPYYRR
PPYYRr
PPYyRR
PPYyRr
PpYYRR
PpYYRr
PpYyRR
PpYyRr
PYr
PPYYRr
PPYYrr
PPYyRr
PPYyrr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
PyR
PPYyRR
PPYyRr
PPyyRR
PPyyRr
PpYyRR
PpYyRr
PpyyRR
PpyyRr
Pyr
PPYyRr
PPYyrr
PPyyRr
PPyyrr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
pYR
PpYYRR
PpYYRr
PpYyRR
PpYyRr
ppYYRR
ppYYRr
ppYyRR
ppYyRr
pYr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
ppYYRr
ppYYrr
ppYyRr
ppYyrr
pyR
PpYyRR
PpYyRr
PpyyRR
PpyyRr
ppYyRR
ppYyRr
ppyyRR
ppyyRr
pyr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
ppYyRr
ppYyrr
ppyyRr
ppyyrr
How many (out of 64) will be:
What is the:
- Genotypic ratio?
- Phenotypic ratio?
1PPYYRR:2PPYYRr:2PPYyRR:1PPYYrr:4PPYyRr:2PPYyrr:1PPyyRR:
2PPyyRr:1PPyyrr:2PpYYRR:4PpYYRr:2PpYYrr:4PpYyRR:8PpYyRr:
4PpYyrr:2PpyyRR:4PpyyRr:2Ppyyrr:1ppYYRR:2ppYYRr:
1ppYYrr:2ppYyRR:4ppYyRr:2ppYyrr:1ppyyRR:2ppyyRr:1ppyyrr
27PYR:9PYw:9PgR:3Pgw:9wYR:3wgR:3wYw:1wgw
-
Purple flowers, Yellow peas, Round peas?
white flowers, green peas, wrinkled peas?
-
Purple flowers, green peas, Round peas?
-
white flowers, Yellow peas, Round peas?
Purple flowers, green peas, wrinkled peas?
Heterozygous for all three traits?
9 of 64
PYR PYr
PyR Pyr
pYR pYr
pyR pyr
PYR
PPYYRR
PPYYRr
PPYyRR
PPYyRr
PpYYRR
PpYYRr
PpYyRR
PpYyRr
PYr
PPYYRr
PPYYrr
PPYyRr
PPYyrr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
PyR
PPYyRR
PPYyRr
PPyyRR
PPyyRr
PpYyRR
PpYyRr
PpyyRR
PpyyRr
Pyr
PPYyRr
PPYyrr
PPyyRr
PPyyrr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
pYR
PpYYRR
PpYYRr
PpYyRR
PpYyRr
ppYYRR
ppYYRr
ppYyRR
ppYyRr
pYr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
ppYYRr
ppYYrr
ppYyRr
ppYyrr
pyR
PpYyRR
PpYyRr
PpyyRR
PpyyRr
ppYyRR
ppYyRr
ppyyRR
ppyyRr
pyr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
ppYyRr
ppYyrr
ppyyRr
ppyyrr
How many (out of 64) will be:
What is the:
- Genotypic ratio?
- Phenotypic ratio?
1PPYYRR:2PPYYRr:2PPYyRR:1PPYYrr:4PPYyRr:2PPYyrr:1PPyyRR:
2PPyyRr:1PPyyrr:2PpYYRR:4PpYYRr:2PpYYrr:4PpYyRR:8PpYyRr:
4PpYyrr:2PpyyRR:4PpyyRr:2Ppyyrr:1ppYYRR:2ppYYRr:
1ppYYrr:2ppYyRR:4ppYyRr:2ppYyrr:1ppyyRR:2ppyyRr:1ppyyrr
27PYR:9PYw:9PgR:3Pgw:9wYR:3wgR:3wYw:1wgw
-
Purple flowers, Yellow peas, Round peas?
white flowers, green peas, wrinkled peas?
Purple flowers, green peas, Round peas?
-
white flowers, Yellow peas, Round peas?
-
Purple flowers, green peas, wrinkled peas?
Heterozygous for all three traits?
9 of 64
PYR PYr
PyR Pyr
pYR pYr
pyR pyr
PYR
PPYYRR
PPYYRr
PPYyRR
PPYyRr
PpYYRR
PpYYRr
PpYyRR
PpYyRr
PYr
PPYYRr
PPYYrr
PPYyRr
PPYyrr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
PyR
PPYyRR
PPYyRr
PPyyRR
PPyyRr
PpYyRR
PpYyRr
PpyyRR
PpyyRr
Pyr
PPYyRr
PPYyrr
PPyyRr
PPyyrr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
pYR
PpYYRR
PpYYRr
PpYyRR
PpYyRr
ppYYRR
ppYYRr
ppYyRR
ppYyRr
pYr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
ppYYRr
ppYYrr
ppYyRr
ppYyrr
pyR
PpYyRR
PpYyRr
PpyyRR
PpyyRr
ppYyRR
ppYyRr
ppyyRR
ppyyRr
pyr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
ppYyRr
ppYyrr
ppyyRr
ppyyrr
What is the:
- Genotypic ratio?
- Phenotypic ratio?
How many (out of 64) will be:
-
Purple flowers, Yellow peas, Round peas?
white flowers, green peas, wrinkled peas?
Purple flowers, green peas, Round peas?
white flowers, Yellow peas, Round peas?
1PPYYRR:2PPYYRr:2PPYyRR:1PPYYrr:4PPYyRr:2PPYyrr:1PPyyRR:
2PPyyRr:1PPyyrr:2PpYYRR:4PpYYRr:2PpYYrr:4PpYyRR:8PpYyRr:
4PpYyrr:2PpyyRR:4PpyyRr:2Ppyyrr:1ppYYRR:2ppYYRr:
1ppYYrr:2ppYyRR:4ppYyRr:2ppYyrr:1ppyyRR:2ppyyRr:1ppyyrr
27PYR:9PYw:9PgR:3Pgw:9wYR:3wgR:3wYw:1wgw
-
Purple flowers, green peas, wrinkled peas?
-
Heterozygous for all three traits?
3 of 64
PYR PYr
PyR Pyr
pYR pYr
pyR pyr
PYR
PPYYRR
PPYYRr
PPYyRR
PPYyRr
PpYYRR
PpYYRr
PpYyRR
PpYyRr
PYr
PPYYRr
PPYYrr
PPYyRr
PPYyrr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
PyR
PPYyRR
PPYyRr
PPyyRR
PPyyRr
PpYyRR
PpYyRr
PpyyRR
PpyyRr
Pyr
PPYyRr
PPYyrr
PPyyRr
PPyyrr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
pYR
PpYYRR
PpYYRr
PpYyRR
PpYyRr
ppYYRR
ppYYRr
ppYyRR
ppYyRr
pYr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
ppYYRr
ppYYrr
ppYyRr
ppYyrr
pyR
PpYyRR
PpYyRr
PpyyRR
PpyyRr
ppYyRR
ppYyRr
ppyyRR
ppyyRr
pyr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
ppYyRr
ppYyrr
ppyyRr
ppyyrr
How many (out of 64) will be:
What is the:
- Genotypic ratio?
- Phenotypic ratio?
1PPYYRR:2PPYYRr:2PPYyRR:1PPYYrr:4PPYyRr:2PPYyrr:1PPyyRR:
2PPyyRr:1PPyyrr:2PpYYRR:4PpYYRr:2PpYYrr:4PpYyRR:8PpYyRr:
4PpYyrr:2PpyyRR:4PpyyRr:2Ppyyrr:1ppYYRR:2ppYYRr:
1ppYYrr:2ppYyRR:4ppYyRr:2ppYyrr:1ppyyRR:2ppyyRr:1ppyyrr
27PYR:9PYw:9PgR:3Pgw:9wYR:3wgR:3wYw:1wgw
-
Purple flowers, Yellow peas, Round peas?
white flowers, green peas, wrinkled peas?
Purple flowers, green peas, Round peas?
white flowers, Yellow peas, Round peas?
Purple flowers, green peas, wrinkled peas?
-
Heterozygous for all three traits?
8 of 64
PYR PYr
PyR Pyr
pYR pYr
pyR pyr
PYR
PPYYRR
PPYYRr
PPYyRR
PPYyRr
PpYYRR
PpYYRr
PpYyRR
PpYyRr
PYr
PPYYRr
PPYYrr
PPYyRr
PPYyrr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
PyR
PPYyRR
PPYyRr
PPyyRR
PPyyRr
PpYyRR
PpYyRr
PpyyRR
PpyyRr
Pyr
PPYyRr
PPYyrr
PPyyRr
PPyyrr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
pYR
PpYYRR
PpYYRr
PpYyRR
PpYyRr
ppYYRR
ppYYRr
ppYyRR
ppYyRr
pYr
PpYYRr
PpYYrr
PpYyRr
PpYyrr
ppYYRr
ppYYrr
ppYyRr
ppYyrr
pyR
PpYyRR
PpYyRr
PpyyRR
PpyyRr
ppYyRR
ppYyRr
ppyyRR
ppyyRr
pyr
PpYyRr
PpYyrr
PpyyRr
Ppyyrr
ppYyRr
ppYyrr
ppyyRr
ppyyrr
Punnett Square
Practice/Homework
Complete the worksheet.
Check the website for the answers.
- Ask questions if you don’t understand.
- Pay attention to the process so you can get
it right.
Wednesday February 6, 2013
Copy onto your ‘Quizzie’ paper the following question. Answer it and save it to turn in. If you don’t
know an answer, get a book and find it or review with a friend. Blanks will count against you and
wrong answers don’t help you.
• Quizzie
• Q1: If a mom that’s homozygous recessive for hair color (she’s
blonde) and a dad is heterozygous for hair color (he has black hair),
what will be the possible genotypes of any children they have?
Show this with a Punnett Square.
• Q2: What chance do the children have to get blonde hair?
• Q3: What are the ratios for the genotypes and phenotypes?
50% chance
• ----------------------------of getting
blonde hair
b
b
• Agenda:
• Check Punnett Squares
• Discussion: Test Crosses.
• QL: Test Crosses
B
Bb
Bb
GR: 1:1
b
bb
bb
PR: 1:1
Punnett Squares: Answers
P
PP
PP
#3
100%PP
Phenotypic Ratio: 1Purple:0(all);100%Purple
GR: 1Yy:0
PR: 1Yellow:0
100% Yy
100%yellow
#2
#4
P
P PP
p
Pp
p Pp
pp
#1
P
P PP
P PP
Genotypic Ratio: 1PP:0 (all)
G
g Gg
g
gg
g Gg
gg
GR: 1Gg:1gg
50%Gg, 50%gg
PR: 1green: 1yellow; 50%green, 50%yellow
Y
Y
y Yy
Yy
y Yy
Yy
GR: 1PP:2Pp:1pp; 25%PP, 50% Pp, 25%pp
PR: 3purple: 1white; 75%purple, 25%white
Thursday February 7, 2013
Copy onto your ‘Quizzie’ paper the following question. Answer it and save it to turn in. If you don’t
know an answer, get a book and find it or review with a friend. Blanks will count against you and
wrong answers don’t help you.
• Quizzie #3: Imagine you are a farmer and wanted to start selling green sweet peas (what
Mendel produced and studied). You buy a pea plant that is sold to you as a true-breeding
green pea plant for nice round peas. You are skeptical because the guy who sold it to you
seemed shady. You are intending to plant several acres with this plant’s seeds and have a
lucrative business.
• Q1: What specific technique could you perform to find out exactly what the
genotype of your plant is?
• Q2: What phenotype would you want all the offspring from this technique to be?
• Q3: If the offspring of a test cross all have the dominant trait, is the genotype of the
individual being tested heterozygous or homozygous?
-------------------• Agenda:
• Discussion: Probabilities
• Penny Genetics Lab
• Hand in Testcross MiniLab
Using Probability
• A Punnett square shows the possible outcomes of a cross,
but it also is used to calculate the probability of each
outcome.
• Probability is the likelihood that a specific event will occur
out of the total number of events.
• Probability can be calculated and expressed in many ways.
• Probability can be expressed in words, as a decimal, as a
percentage, or as a fraction.
Using Probability, continued
• Probability formulas can be used to predict the probabilities
that specific alleles will be passed on to offspring.
• Probabilities are usually expressed as decimals or as
percentages although fractions are okay.
• 2/4 = ½
• ¼
• ¾
= 0.5
= 0.25
= 0.75
= 50%
= 25%
= 75%
• The possible results of a heterozygous cross (which is trying
to predict the genotypes of offspring from the mating of two
heterozygotes) are similar to those of flipping two coins at
once.
• This is where we will begin our testing.
Using Probability
• Punnet Squares are nice tools to use but the real question
remains…
• How can you be sure that the Punnet squares accurately show
how genetics really works?
• The solution will hopefully be revealed in the next exercise…
• Penny Genetics
Penny Genetics Lab
Testing the validity of Punnett Squares.
• Get into groups of two (max). Get one packet per pair.
• In groups of two you will perform an investigation into whether
Punnett Squares can be used to predict randomness of nature.
• For the next 5 minutes… Completely read the lab intro & skim the
rest. I’ll answer questions then.
• A Punnett Square makes a prediction but does it match the randomness in
nature? Perform a Punnett Square and then flip coins to see if they match.
• Part I:
First: Figure out the PHENOTYPES based upon the description.
Second: Predict if the PUNNETT SQUARE will match the COIN FLIPS
Third: Complete the PUNNETT SQUARE (this is the prediction)
Fourth: Flip the COINS 100x.
Fifth: COMPARE the two.
• You may write on the lab, but don’t lose it or you’ll have to hand
write it or print it off the website.
• Your objective is to get through all of Part I & Part II if everything
goes good so work diligently! Complete everything today to save
yourself homework.
• This Lab is worth 125 points. Due Friday.
Monday February 11, 2013
Copy onto your ‘Quizzie’ paper the following question. Answer it and save it to turn in. If you
don’t know an answer, get a book and find it or review with a friend. Blanks will count against
you and wrong answers don’t help you.
• Quizzie #4:
In pea plants, tallness (T) is dominant to shortness (t). Crosses between plants with these traits
can be analyzed using a Punnett square similar to the one shown below.
T
t
T
1
2
t
3
4
• Q1: Complete this Punnett Square.
• Q2: Box 2 and box ____________________ in the Punnett square represent plants that
would be heterozygous for the trait for tallness.
• Q3: The phenotype of the plant that would be represented in box 4 of the Punnett square
would be ____________________.
--------------------------------------------------------------------------------------------------------------------------------
• Agenda:
• Discussion: Pedigrees
• In-class/ HW Activity Pedigree Analysis
• Penny Genetics DUE. Turn these in to the inbox.
Applications of Mendelian Genetics
• Families can sometimes be surprised when recessive traits “pop up”
out of seemingly nowhere.
• Not knowing how genetics works can stress people out
unnecessarily.
• If a child expresses, shows, a recessive trait but the parents express
the dominant trait what are the genotypes of the parents & how can
you figure this out?
The point of using a Punnett
Square
• Punnett squares are useful when predicting the
ratios of offspring.
• For example, is you want to know the probability
of how many siblings in your family can have the
phenotype of black hair your can calculate that if
you know the genotypes of your parents.
• But what if you don’t know their genotypes?
• The 1st option is using a test cross.
Test Cross Mini Lab
• If you aren’t sure what the genotype
of a parent showing a dominant trait
is you perform a test cross.
• In a test cross, you always cross the
unknown with a homozygous recessive
individual.
• The difference is in the “?” allele.
• What does it mean if half of the offspring
show the recessive trait?
B
?
b
Bb
b?
b
Bb
b?
Test Cross
• The test-cross mating can have two possible phenotype outcomes.
• All dominant offspring
• What would the “?” have to be?
B
?
b
Bb
b?
b
Bb
b?
Test Cross
• The test-cross mating can have two possible phenotype outcomes.
• Half recessive offspring.
• What would the “?” have to be?
B
?
b
Bb
b?
b
Bb
b?
Genes Linked Within
Chromosomes
• Many traits do not follow Mendel’s laws because he studied
the simplest kinds of heredity where characters are
determined by independent genes.
• Genes that are close together, as well as the traits they
determine, are said to be linked.
• During meiosis, genes that are linked (close together) on the
same chromosome are less likely to be separated than
genes that are far apart.
• We discussed this in Punnett Squares when we challenged
independent assortment.
• Linked genes tend to be inherited together.
• Sex-linked genes are those genes inherited together based
upon gender chromosomes.
Not-Linked
Not-Linked
Linked
Linked
Linked v Non-linked
What is Sex-Linked? How does it happen?
X
Y
STANDARD GENDER
DISTRIBUTION
PROBABILITY =
50% MALE - 50% FEMALE
X
XX
XY
X
XX
XY
X
Y
STANDARDCGENDER
DISTRIBUTION
PROBABILITY = 50/50
BUT ADD INTO THE MIX
COLOR-BLINDNESS,
C XCXC XCY
WHICH IS ONLY
FOUND ON THE ‘X’
CHROMOSOME
c XCXc XcY
X
X
A Sex-Linked Trait
Red-Green Color Blindness
Can you see the
numbers?
Trace from x to x…
there’s a line there.
X
X
Sex-Linked Gene
Inheritance
Notice the distribution
of the alleles.
In this case you must
take two things into
account.
Sex & the allele.
XC
Xc
XC
XC
XCXC
Y
XC
XcY
Test Crosses & Linkage Exercises
• Complete the worksheet for homework.
Show the cross of a man who has hemophilia
with a woman who is a carrier along with the
genotypic/phenotypic ratios for the possible
offspring.
GR: 1XHXh:1XhXh:1XHY:1XhY
PR: 2 F Norm: 1 M Norm: 1 M Hemophilia
XH
Xh
Xh
XHXh
XhXh
Y
XHY
XhY
The Royal Disease
• European Royalty in the 19th & 20th
centuries came with a price.
• Although many were spared the horrible
tragedy of bleeding to death, some were
not so lucky due to the pervasive recessive
X-linked trait hemophilia.
Hemophilia in History:
Study in pedigree.
The most famous
example.
Men who died of Hemophilia in Order of Death
Name
Death
Relation to Queen Victoria
Prince Friedrich of Hesse and by Rhine
29-May-1873
grandson
The Prince Leopold, Duke of Albany
28-Mar-1884
son
Prince Heinrich Friedrich of Prussia
26-Feb-1904
great grandson
Lord Leopold Mountbatten
23-Apr-1922
grandson
Prince Rupert of Teck
15-Apr-1928
great grandson
Infante Gonzalo of Spain
13-Aug-1934
great grandson
Alfonso, Prince of Asturias
6-Sep-1938
great grandson
Prince Waldemar of Prussia
2-May-1945
great grandson
Pedigrees. Genetics Tool
• Now:
• Karyotyping: Detect obvious chromosome
abnormalities
• Genetic testing: Detect hidden mutations in DNA
• Some disabilities aren’t fatal
• Red-green color blindness
• Albinism
• But others are:
• Hemophilia
• Duchene muscular dystrophy
• Do you think it’s important to study these diseases
and how they are passed through families?
Pedigrees
• Other than determining the probabilities of
Mendelian traits being inherited and displayed in
a monohybrid cross (aka Punnett Square),
geneticists use another tool, called a pedigree, to
identify patterns of inheritance in multiple
generations.
http://www.youtube.com/watch?v= W7x1ETPkZsk
Using a Pedigree
•
•
•
Mendel observed several generations of pea plants to help
identify some trends in heredity.
His observation of inheritance is a good example of
performing an isolated family history study to see how a
trait is inherited.
A pedigree is a similar study, except over many generations.
•
A pedigree is a diagram that shows several generations of a
family and the occurrence of certain genetic characteristics.
•
A primary reason a pedigree is used is to help a family
understand a genetic disorder and how it’s passed on.
•
A genetic disorder is a disease or disorder that can be
inherited.
Using a Pedigree
• A pedigree can help answer questions about three
aspects of inheritance:
1.Sex linkage
- To identify which deleterious genes are located on the
X chromosome (deleterious = BAD)
2.Dominance
- Identify the dominant or recessive alleles
3.Heterozygosity (aka a Carriers for a disease)
- Help determine the genotype of parents.
Hemophilia
High blood pressure
DMD
Congenital night blindness
• The sex chromosomes, X and Y, carry genes for many
characters other than gender.
Using a Pedigree:
Sex Linked Genes
• A sex-linked gene is located on either an X or a Y
chromosome.
• Traits that are not expressed equally in both sexes are
commonly sex-linked traits.
• Examples:
• Colorblindness: a sex-linked trait that is expressed more in males than
in females.
• Baldness: expressed more in males
• Any other ones?...
Using a Pedigree: Dominance,
Carriers
• Dominance: If a person has a trait that is autosomal (meaning
what?) and dominant and has even one dominant allele, he or
she will show the trait.
• Dominant traits have a tendency to show up more often than not.
• They do follow Mendelian probabilities though.
• Heterozygosity: If a person is either heterozygous or
homozygous dominant for an autosomal gene, his or her
phenotype will show the dominant trait.
• If a person heterozygous for a recessive trait he or she will not
show the trait but can and may pass it on.
• Why would the trait not be passed on?
• There is a 50/50 chance of passing it on.
• Persons carrying the recessive allele but not displaying the
trait are called carriers.
Pedigree Basic Symbols
Horizontal lines show
relationships that
produced offspring
The character key:
Vertical lines
show
offspring from
the pair
A female
A male
A female with trait
A male with trait
Carrier (ex. Male)
Group Questions. Using alleles A, a, you have 5 minutes to
discuss with your group and answer.
1. What is the sex of individual #3?
2. Who shows the trait?
3. Is this trait dominant or
recessive? Why?
4. What is the genotype of
individual #3?
5. What are the genotypes of Mom
& Dad?
6. Who can you not determine the
genotype for?
7. BONUS: Is this trait sex-linked?
How do you know?
1. Female
2. Female #3
3. Recessive or mom & dad would
have it.
4. aa
5. Aa, Aa
6. Siblings 1, 2, & 4
7. No, otherwise dad would have
the trait too. One of the X’s for #3
would have to come from dad.
Using a Pedigree: Strategy
Remember…
• If a person is homozygous recessive, his or her phenotype will
show the recessive trait.
• A recessive trait in a child shows that both parents were
heterozygous carriers of that recessive allele.
• Dominant traits show up more often than recessive.
• Look for the people displaying the trait! Using logic you can
determine the parent’s genotypes  then the siblings.
1. Pedigree Analysis Practice. (CW/HW: 25pts)
1.
Example 1 has 2 unknowns, not 9.
2. Pedigree Mini-Lab exercise. (HW)
You may work in groups of two and you can write on the
worksheet.
Problems should be worked out today and this is due tomorrow.
It is worth 25 pts (1/4 lab).
Summary
• A Punnett square shows all of the genotypes that could
result from a given cross.
• Probability formulas can be used to predict the
probabilities that specific alleles will be passed on to
offspring.
• A pedigree can help answer questions about three
aspects of inheritance: sex linkage, dominance, and
heterozygosity.
Genotypes
Allele combo
FF
Ff
Phenotypes
Trait
Ff
f f
Aa
Aa
aa
Aa
??
aa
??
Aa
??
??
Aa
??
Aa
Aa
aa
??
aa
??
??
Aa
aa
Aa
Aa
??
aa
??
Aa
Section 12.1-12.3 Quiz
•
•
•
•
•
•
•
•
•
The quiz says “12. & 12.2” but it’s for sections 12.1-12.3.
Write all answers on a separate sheet of paper.
Do not write on the quiz.
If you write on the quiz you will get a zero.
You may use books.
Correct answers are worth 1 pt. ea.
You do not need to write complete sentences.
Double check your work before you turn them in.
Turn in your answers to the test/quiz tray in the back.
________
________
________
________
________
________
________
2
otype
_____
______
______
______
______
______
______