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Do Now—2.5.14
Turn in your Family
Pedigree to front
Is this trait autosomal dominant or autosomal
recessive? Why?
Autosomal dominant
aa
aa
aa
If both parents have the trait
but the child does not, then
the trait must be dominant
Exit Slip
Is this pedigree for a recessive trait?
No!
Aa
Aa
aa
aa
aa
aa
If both parents have the trait but the child
does not, then the trait must be dominant
Unit 3: Sickle Cell Disease
3.3 and 3.4
Genetics Review for Quiz
2.5.14
Objectives
 SWBAT
review for their group quiz.
Diseases

Sickle cell disease is an autosomal
recessive disorder (s = sickle allele, S =
normal allele)
Diseases
Sickle cell disease is an autosomal
recessive disorder (s = sickle allele, S =
normal allele)
 Best disease is an autosomal dominant
disorder (B = Best allele, b = normal
allele).

Diseases
Sickle cell disease is an autosomal
recessive disorder (s = sickle allele, S =
normal allele)
 Best disease is an autosomal dominant
disorder (B = Best allele, b = normal
allele).
 Hemophilia is a X-linked recessive disorder
(Xh = hemophilia allele, XH = normal allele).

Sickle Cell Prevalence

More than 2.5 million Americans have the the
sickle cell allele
–
–
1 in 12 African Americans have the sickle cell allele
1 in 172 Latinos have the sickle cell allele
Sickle Cell Prevalence
Malaria is caused by a parasite carried by
mosquitoes. The parasite uses red blood cells to
reproduce.
The parasites cannot reproduce in sickle cell
red blood cells, so people with the sickle cell
allele did not get malaria.
3.3.1: How is DNA Passed Through
the Generations?
3.3.1: How is DNA Passed Through
the Generations?
Mitosis makes body (somatic) cells with 46 chromosomes.
If the DNA did not replicate first then when the cell
divided there would only be 23 chromosomes in the cell
Sex (gamete) cells come together during fertilization to
make a baby with 46 chromosomes. Each gamete needs
to have 23 chromosomes because 23 + 23 = 46.
3.3.1: How is DNA Passed Through
the Generations?
Sickle cell is a recessive disorder. Best disease is a
dominant disorder. For sickle cell disease you need
to have two sickle alleles (ss). For Best disease
you only need one Best allele to have the disorder
(Bb or BB)
3.3.1: How is DNA Passed Through
the Generations?
Hemophilia is a X-linked recessive disorder. Males only have
one X so unlike females that must inherit two Xh alleles, if
males inherit just one they will have the disorder.
Ss
Ss
ss
The parents can be
carriers for sickle cell
disease and if both of
the parents pass the
sickle allele, then the
child would have sickle
cell disease.
3.3.1: How is DNA Passed Through
the Generations?
3.3.1: How is DNA Passed Through
the Generations?
3.4.1: Family Inheritance
prospective parents.
3.4.1: Family Inheritance
pon Anna’s family pedigree that you created
evious activity, determine her mother’s
genotypes and phenotypes related to sickle
mia. Explain your reasoning by completing
gree shown on the right, and describe the
on you used to determine her phenotype.
3.4.1: Family Inheritance
Sickle cell is a recessive disorder because you need
to have two sickle alleles (ss) to show the
phenotype (sickle cell disease).
S
s
s
s
Ss ss
Ss
ss
There is a 50%
probability that the
child will have sickle
cell and a 50% chance
of being a carrier.
3.4.1: Family Inheritance
aa
Aa
A?
Aa Aa
Children have the trait but
A? the parent does not (the
trait skips generations)
A?
Aa
Aa
aa
A?
aa
The trait must be
A?
autosomal recessive
inheritance.
3.4.1: Family Inheritance
Tt
tt
tt
Tt
tt
tt tt
7 people
Tt Tt
7 people
Tt tt
tt
0 people
tt tt
Tt
Tt
tt
10 people
3.4.1: Family Inheritance
Activity 3.4.2: What is the
Probability?
Name: ________________________
Date: ______________Period: _____
Activity 3.4.2: What is the Probability?
Introduction
Sickle cell anemia is an inherited recessive disorder. If the pattern of how the trait is inherited and
the individual’s family pedigree are known, doctors and genetic counselors can calculate the
probability that an individual will express a trait. In Activity 3.3.1 you learned that each parent has
two copies of every chromosome. Therefore, there is a 50% chance of either chromosome being
passed to a child (just as with a coin there is a 50% chance it will be heads and a 50% chance it
will be tails when it lands after being tossed in the air). The science of genes, heredity, and the
variation of organisms is called genetics, and the biologists who study genetics are called
geneticists. Using their understanding of whether a trait is dominant or recessive, geneticists can
predict the likelihood of the inheritance of particular traits.
One of the easiest ways to calculate the mathematical probability of inheriting a specific trait is
called a Punnett square. A Punnett square is a simple graphical way of discovering all of the
potential combinations of genotypes, given the genotypes of the parents. It also can be used to
determine the percent chance of each genotype’s occurrence.
Activity 3.4.2: What is the
Probability?
Probability the child will have sickle cell disease is ______________________.
Probability the child will be a carrier for sickle cell disease is __________________.
Conclusion
1. How does your predicted percent chance that an offspring would have sickle cell anemia or be
a carrier compare to your experimental results?
The predicted probability of sickle cell anemia is 50% (2/4) and the
carrier prediction is 50% (2/4). The experimental results are 50% sickle
cell anemia and 50% carrier. There was no difference in experimental
and expected results, but there could have been a difference.
2. Explain how a genetics counselor or a doctor could use these calculations of probability to
counsel prospective parents.
Although the predicted percentage is 50-50 for sickle cell anemic
offspring and carrier offspring, allele assortment is random and a
parent can always have more or less than the expected amount. The
calculations are just a probability or likelihood of having an offspring
with a particular phenotype.
counsel prospective parents.
Activity 3.4.2: What is the
Probability?
3. Based upon Anna’s family pedigree that you created
in the previous activity, determine her mother’s
possible genotypes and phenotypes related to sickle
cell anemia. Explain your reasoning by completing
the pedigree shown on the right, and describe the
information you used to determine her phenotype.
Anna’s mother has a
genotype of Ss and a
phenotype of a sickle cell
carrier. Anna’s mother must
be Ss because she passes
an s allele to Anna and a S
allele to Eric.
Smiley Face Genetics
Name: ________________________
Date: ______________ Period: _____
Heredity is the passing on of traits from parents to offspring. Humans have two of every kind of gene, one
from their mother and one from their father. Only one gene from each parent is passed to each offspring for a
particular trait. The different forms of a gene are referred to as alleles. Some alleles are dominant while others
are recessive. Dominant alleles overpower recessive alleles and only one allele is needed for the offspring to show
the trait. Recessive traits are only seen in the offspring if both parents contribute a recessive allele.
Smiley Face Baby Activity
Traits are passed from parents to their offspring randomly to gametes during meiosis. Male gametes are
sperm. Female gametes are eggs. Use the flip of a coin to determine which alleles the parents will pass to the
gametes that will make their offspring (baby). If the coin flip lands on heads select the dominant allele. If the coin
lands on tails, select the recessive allele. Circle the selected alleles in the chart below.
s
s
b
b
y
y
h
h
Smiley Face Genetics
randomly
Traits are passed from parents to their offspring ______________. Parents pass their alleles to their offspring
gametes
through their _________________. Each gamete will contain one ________. When the two gametes merge,
allele
1
fertilization has occurred and a zygote has formed. The zygote will grow into a baby. The baby will need ______
2
dominant allele(s) to show a trait and ______ recessive allele(s) to show a trait. If a person has two of the same
alleles they are considered homozygous, if the alleles are different then they are considered heterozygous.
1.
2.
3.
recessive
heterozygous
dominant
Homozygous dominant
H is a ____________ allele. HH would be considered __________________________________.
egg
Bb
The father’s B allele would be in sperm
_________. The mother’s b allele would be in an _____. The baby = ______.
b is a ____________ allele. Bb would be considered _____________________________________.
Smiley Face Genetics
Genotype Questions
1.
XY
Bb
bb
Yy
yy
Hh
hh
XX
What is the genotype for a male? _________ What is the genotype for a female? __________
BB or Bb
bb
hh Hairy smiley face? _________________
HH or Hh
What is the genotype for a bald smiley face? ____________
2. What is the genotype for a smiley face with brown eyes? _______________ Blue eyes? ______________
3.
4. For which traits does your baby have homozygous dominant alleles?
_______________________________________________________________________________
5. For which traits does your baby have homozygous recessive alleles?
_______________________________________________________________________________
6. For which traits does your baby have heterozygous alleles?
____________________________ ___________________________________________________
Now that you know the genotype of your offspring, you can determine the phenotype of the offspring. The
phenotype is the manifestation of the trait. Traits can be the physical appearance or behavioral. For example, a
behavioral trait would be ‘snoring’ or ‘easily frustrated’. However, a physical trait are like the traits in this activity,
nose shape or skin color.
Smiley Face Genetics
Punnett Square
The following diagram is a Punnett square. Punnett squares illustrate all the possible combinations of alleles an
offspring may receive from its parents—the possible genotypes of the offspring.
Probability is the chance that
something will happen. For these
parents, there is a 75% chance
that the offspring will have brown
eyes, and a 25% chance of blue
eyes.
1. What is probability of having a
child with brown eyes? Blue eyes?
50% brown,
50% blue
b
b
2. What is probability of having a
child with brown eyes? Blue eyes?
100% brown,
0%BblueB
3. What is probability of having a
child with brown eyes? Blue eyes?
100% brown,
0%Bblue B
B
Bb Bb
b
Bb Bb
B
BB BB
b
bb bb
b
Bb Bb
b
Bb Bb
Smiley Face Genetics
Pedigree Analysis
A pedigree is a diagram of family relationships that uses symbols to represent people and lines to
represent genetic relationships. These diagrams make it easier to
visualize relationships within families, particularly large extended
families. Pedigrees are often used to determine the mode of
inheritance (dominant, recessive, etc.) of genetic diseases.
In a pedigree, squares represent males and circles represent
females. Horizontal lines connecting a male and female represent
mating. Vertical lines extending downward from a couple represent
their children. In the pedigree above, the grandparents had two
children, a son and a daughter. The son had the trait. One of his four
children also had the trait. Generations are drawn underneath the
parental generations, with the oldest generation at the top of the
pedigree and the oldest individuals within a generation drawn furthest to the left.
If the purpose of a pedigree is to analyze the pattern of inheritance of a particular trait, it is
customary to shade in the symbol of all individuals that possess this trait. If someone does not have the
trait leave the person blank. If the person is a carrier they have the allele but do not have the trait so
they are only half shaded—when a person is heterozygous for a recessive disease. Carriers are not
always shown in a pedigree. If you cannot determine someone’s genotype you but a ‘?’.
aa"
AA"
A? = AA or Aa
(Do not
Aa" know)
aa"
Autosomal Dominant (A)
-Person can be homozygous dominant or heterozygous to show trait
-At least one of the parents must have trait
-If you cannot determine someone’s allele you but a ‘?’.
*Notice that carriers are not
Autosomal
Recessive
(a)
always
shown
as half shaded
-Person must be homozygous recessive to show trait
-Parents do not have to have the trait for a child to have it
-People can be carriers (have allele but not trait = heterozygous)
-If you cannot determine someone’s allele you but a ‘?’.
Aa"
Aa"
aa"
A?"
Smiley Face Genetics
Pedigree Practice: Autosomal Dominant (Shaded person can be homozygous dominant or heterozygous)
Write the genotypes of each person in the pedigree below assuming a dominant trait.
aa
A?
A?
aa
Aa
Aa
aa
Aa
Aa
A?
aa
Pedigree Practice: Autosomal Recessive (Shaded person must be homozygous recessive)
Write the genotype of each individual next to the symbol. If an individual is a carrier, then indicate it.
Aa
Aa
aa
A?
A?
aa
Aa
Aa
Aa
aa
Homework
Quiz on 3.3 and 3.4 tomorrow –
STUDY FOR YOUR GROUP QUIZ!!!
 Group
Exit Slip
 How
do you plan on studying for the
quiz tomorrow?
 What
grade do you think your group
will earn?
 How
do you plan to work together to
succeed on your quiz?
Community Builder
 Two
truths and a lie
 Think of two things that are true about
you but sound like a lie. Then you are
going to share with the class the three
statements (two truths and a lie), we
are going to try and determine what
the lie is!!!!