Transcript Genetics ppt

Bell Ringer
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Which features do you have that match your mother?
Your father?
Which of the following features do you have?
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Widow’s Peak?
Ability to roll your tongue?
Attached earlobes?
Simple Genetics
Exploring How Traits are Passed On
Punnett Squares
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In order to determine the traits that a person might
inherit, we use a simple diagram called a Punnett Square!
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Punnett Squares give us the probability of an offspring having
particular traits
Pieces of the Puzzle
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Before completing a square, you must know the
components
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Allele-An allele is a variant form of a gene
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Dominant-A dominant allele show their effect even if there is
only one copy of the allele (think of them as being strong!)
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Dominate alleles are denoted by a capital letter (ex. A)
Recessive- A recessive allele will only show up if no dominant
alleles are in place (think of them as being weak!)
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Humans inherit one allele from each parent that determines a trait
For example, alleles might determine if you have curly or straight hair,
are tall or short, etc.
Recessive alleles are denoted by a lowercase letter (ex. a)
Dominant and Recessive alleles pair together to determine a trait
(ex. AA, Aa, aa)
Homozygous vs. Heterozygous
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So…alleles pair together (AA, aa, Aa)
Homozygous-if both letters are identical (both dominant
(capital) or both recessive (lowercase)), the alleles are
homozygous
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“Homo” means “same”
Ex. Let’s say “A” represents the allele for a widow’s peak, and “a”
represents the allele for a straight hairline
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A person with “AA” would be called homozygous dominant
A person with “aa” would be called homozygous recessive
Heterozygous-if both letters are different (one dominant
(capital) and one recessive (lowercase)), the alleles are
heterozygous
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“Hetero” means “different”
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A person with “Aa” would be heterozygous
Would they have a widow’s peak or a straight hairline?
Phenotype and Genotype
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All of these allele combinations tell us the phenotype and
genotype of a person
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Genotype-The genetic, inheritable information of an
organism
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Example: A person’s genotype is Aa (heterozygous); they can
pass on either a dominant allele or a recessive one to their
children.
Phenotype-The outward, physical appearance of an
organism
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Example: A person has a widow’s peak
Let’s Practice
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Dominant or Recessive?
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Heterozygous or Homozygous?
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A
b
B
AA
Bb
cc
Phenotype or Genotype?
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She is homozygous recessive (rr)
She has blue eyes
Building a Punnett Square
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Consider the following alleles for pea plant color:
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AA (Yellow-homozygous dominant)
Aa (Yellow-heterozygous)
aa (Green-homozygous recessive)
Let’s say you had two pea plants, both heterozygous
yellow (Aa), and you wanted to know what color
plants would be produced. How would you find out?
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Set up and Punnett Square
Building a Punnett Square
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What we know: Both parent plants are Aa
So, cross Aa x Aa will be carried out in the Punnett
Square below:
Mother
Father
*Note: It doesn’t
matter where you
set up the
mother/father, the
results will be the
same!
Building a Punnett Square
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So, how do you carry out a Punnett Square?
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Father’s letters cross to the right
Mother’s alleles cross down, filling in the squares to complete
Mother
the allele
AA Aa
Father
Aa
aa
*Notice each
potential
combination has
one allele from
mom and one
from dad
Interpreting the Final Square
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Once the square is finished, always determine the
genotype and phenotype ratios of the possible offspring
Genotype: 1:2:1
-1 AA, 2 Aa, and 1aa
Phenotype: 3:1
-3 Yellow, 1 Green
Note: These ratios are equally probable for each offspring, meaning each offspring has
the same chance of inheriting the traits!!
Practice
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Complete the Cross: Tt x tt
Genotype:
Phenotype:
Practice
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W= long whiskers (dominant)
w=short whiskers (recessive)
What is the probability of producing offspring that have
short whiskers from a cross of two long whiskered seals,
one homozygous dominant and one heterozygous?
Genotype:
Phenotype:
A Few Notes on Genetics…
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Some traits are controlled by more than one pair of
genes, and so present a wide range of phenotypes
(ex. Skin, hair, eye color)
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All traits depend on both genetic and environmental
factors
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Heredity determines your traits, but the environment may play
a role in how they act
Bell Ringer
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W= long whiskers (dominant)
w=short whiskers (recessive)
What is the probability of producing offspring that have
short whiskers from a cross of two seals, one
homozygous recessive and one heterozygous?
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Draw the Punnett Square
Determine the Genotype ratios
Determine the Phenotype ratios
Answer the above question
Bell Ringer
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W= long whiskers (dominant)
w=short whiskers (recessive)
What is the probability of producing offspring that have
short whiskers from a cross of two seals, one
homozygous dominant and one heterozygous?
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Draw the Punnett Square
Determine the Genotype ratios
Determine the Phenotype ratios
Answer the above question
Genetic Diseases
How Diseases are Carried Through Generations
Dominant and Recessive
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If a disease is recessive, both parents have to pass on a
mutated allele to the offspring
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Those who are heterozygous (Aa) are carriers, meaning they
have the mutated allele and can pass it on, but are healthy
themselves
If a disease is dominant, only one parent has to pass on
the mutated allele for offspring to have it
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Can a person with a dominant disease be a carrier?
Let’s take a look at some specific genetic
diseases…
Cystic Fibrosis (cf)-Recessive
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This disease causes a mucus
buildup in the lungs and
digestive system
Those affected have difficulty
breathing and poor growth
Common in those with
European Ancestry
Live expectancy up to 35
years thanks to gene therapy
Sickle Cell Anemia-Recessive
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This disease affects a person’s
red blood cells
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The odd shape causes the cells
to get stuck in blood vessels
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A mutation causes the cells to be
long and bent (“sickle” shaped)
Cuts off blood flow and circulation
Common in those with African
ancestry
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Carriers are associated with
malaria resistance-we’ll discuss why
later!
PKU-Recessive
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PKU- Phenylketonuria
A condition in which the body is
missing the enzyme that breaks
down phenylalanine, an amino acid
This means it builds up in the
body, which results in mental
deterioration
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Memory loss/identity loss!
People affected have to keep a
low protein diet and have the
enzyme injected regularly
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This must be done for life!
Genetic Disease Punnett Squares
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A woman is concerned that she may develop
Huntington’s Disease because her father has it. What is
the probability that she has Huntington’s?
Note: The mother does not have Huntington’s Disease.
Huntington’s-Dominant
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This disease affects the muscles
of the body
Those affected will slowly have
muscle function decline
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Unfortunately, it often does not
show signs until the person
reaches mid 30s-can take up to
20 years to kill!
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Painful, like a muscle cramp that
won’t go away
Shows up after the person has
already had children, meaning that
they have already passed the allele
Affects all people!
Genetic Disease Punnett Squares
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A woman who is a carrier for Cystic Fibrosis marries a
man who is also a carrier. What is the probability that
they will have a child with Cystic Fibrosis?
Bellringer-4/23/15
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Complete the Genetic Diseases Review Worksheet on
your desk. We will work on this for 30 minutes.
Bellringer-4/24/15
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We have a quiz today.You have 10 minutes to study for
your quiz. Be sure to review:
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Definitions
How to complete Punnett Squares
Genetic Disease patterns and symptoms
Bellringer-4/27/15
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Complete the Punnett Square review sheet on your desk!
Complex Genetics
Codominance, Incomplete Dominance, Sex-Linked Traits, and
Blood Typing
Incomplete Dominance
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Sometimes, one allele is not completely dominant over
another allele
In this case, the offspring are blends of both parents!
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The heterozygote has a unique phenotype because one gene
does not dominate the other
Example: Red Flower (RR) + White Flower (WW)= Pink
Flowers (RW)
Incomplete Dominance
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During incomplete dominance, organisms who are
heterozygous for a trait have the opportunity to pass
either gene to the offspring
Therefore, a cross between two heterozygous organisms
have the following results:
1 RR: 2 Rr: 1 rr
1 Red: 2 Pink: 1 White
Incomplete Dominance Example
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A red carnation is crossed with a white carnation and the
resulting offspring are all pink (indicating incomplete
dominance). What would be the result of a cross between
a pink and a white carnation?
Codominance
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Sometimes, both alleles are equally dominant
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Therefore, both alleles will be expressed in phenotype
In this case, the offspring display the traits of both
parents!
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Example: White Cow (WW) + Brown Cow (BB)= White and
Brown Cow (BW)
Case Study: Sickle Cell Anemia
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Although we discussed Sickle-Cell Anemia’s recessive
inheritance pattern, the disease does display a certain
codominance
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Those homozygous affected (aa) have misshapen cells
Those homozygous unaffected (AA) have normal cells
Those heterozygous (Aa) are unaffected carriers, but can have
some misshapen cells mixed in
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This unique feature means heterozygous individuals are resistant to
severe malaria!
Codominance Example
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A bird with white and blue feathers mates with another
white and blue bird (BW). What are the phenotypic ratios
of the offspring?
Bellringer-4/28/15
 Complete
the bellringer sheet
on your desk!
Blood-Typing
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Human blood types include a codominance pattern
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Humans can have type A, B, AB, or O blood
The alleles involved are two codominant alleles (IA and IB), and
one recessive allele (i)
Genotype
Blood Type
IAIA or IAi
A
IBIB or IBi
B
IAIB
AB
ii
O
Blood Type Practice Problem
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The father is type A homozygous, and the mother is type
O. What are the possible blood types of their children?
Is Parentage Possible?
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Ralph has type B blood and his wife Rachel has type A
blood. They are very shocked to hear that their baby has
type O blood, and think that a switch might have been
made at the hospital. Can this baby be theirs? Explain.
Bellringer-4/29/15
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Write the possible genotypes for the following blood
types:
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Type A: __________ or ___________
Type B: __________ or ___________
Type AB: _________
Type O: _________
Solve: There is a mixup between babies at the hospital.
The baby has type O blood. On set of parents have the
genotypes IAIA and IAi. The other set of parents are a
heterozygous Type A mother and a heterozygous Type B
father. Make the crosses of both sets of parents. Which
set does the baby belong to?
Sex-Linked Traits
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Genes located on the sex chromosomes are called
sex-linked genes
Usually found on the X Chromosome
Because of this, males are much more likely to express a
trait than females, because males only have one X
chromosome!
Sex-Linked Traits
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Let’s take a look at the possible alleles in a recessive sexlinked disease:
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Female: XAXA, XAXa, XaXa
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Male: XAY, XaY
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Notice that the female must inherit 2 recessive copies to display the
trait. It is also possible for females to be carriers of sex-linked traits.
Notice the male does not have a second X to help mask the trait. This
means that if he inherits the recessive copy, he will display the trait!
Because of this, males are much more likely to inherit a
sex-linked trait!!!
Common Sex-Linked Traits
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Hemophilia-A bleeding disorder
that slows the blood clotting
process
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Color-Blindness-The inability to
see color, or perceive color
differences
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Because of its X-linked
inheritance, both of these
conditions are more common in
men
Sex Linked Problems
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Cross a woman carrier for hemophilia to a hemophiliac
man. What percentage of the females could inherit the
trait? Males?
Pedigrees
Inheritance Patterns Through Generations
What is a Pedigree?
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A pedigree is the recorded ancestry of a family
Pedigrees allow us to see the genotypes and inheritance
patterns through the generations of a family
What Does a Pedigree Tell Us?
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Pedigrees can give us insight into how traits are
passed through families. You can tell a lot through a
pedigree. For example:
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The phenotypes and genotypes of individuals
The inheritance pattern.
 If more males are affected, it is likely sex linked
 If there are no carriers and one of the parents must have
it, the disorder is dominant
 If carrier parents produce some affected children, the
disease must be recessive
Pedigree Example Problems
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What type of inheritance pattern is shown below?
What would be the genotype of individual I-1?
Pedigree Example Problems
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What type of inheritance pattern is shown below?
What would the genotypes be of individuals II-1 and III-5?
Bellringer-4/30/15
In guinea pigs, black coat color (B) is
dominant to white coat color (b). What
percentage of the offspring will be white
when a homozygous black guinea pig is
crossed with a homozygous white guinea
pig?
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a.
b.
c.
d.
0%
25%
50%
100%
Sickle cell anemia is a genetic disease caused by an
autosomal recessive gene. If each parent carries one sickle
cell allele, what are the chances that their child will have
sickle cell anemia?
a.
no chance
b.
one in four
c.
two in four
d.
three in four
When Mendel was experimenting with pea plant crosses,
one of the traits that he examined was seed texture. The
two phenotypes are smooth and wrinkled. The totals for
his F2 (small 2) generation was 5,474 smooth and 1,850
wrinkled, yielding a probability ratio of approximately
a) 2:1
b) 3:1
c) 4:1
d) 5:1
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A scientist crossed red roses with white roses (R'R'). The
cross revealed a pattern of incomplete dominance in the
heterozygous condition (Rr). What percent of offspring of
the cross were red roses?
a) 0%
b) 25%
c) 50%
d) 100%
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26. A woman heterozygous for A blood marries a man
heterozygous for B blood. What is the probability that
they will produce offspring with AB blood?
a) 0%
b) 25%
c) 75%
d) 100%
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The inheritance of short wings in Drosophilia fruit flies is an
x-linked, recessive trait. Which would most likely result if a
short winged female mates with a long winged male?
a) All offspring would be short winged
b) All females will be long winged, and all males will be
short winged
c) All females will be short winged, and all males will be
long winged
d) Half of the males and females will be short winged, and
half will be long winged
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Color blindness is inherited as a sexlinked trait in humans.
Use a Punnett Square to complete a cross of a colorblind
male with a female with normal vision who is a carrier of
the trait.