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Chapter
5
Chromosomes and
Inheritance
Lecture Presentation
by Wendy Kuntz
© 2015 Pearson Education, Inc.
Chapter 5 Chromosomes and Inheritance:
Unit Hyperlinks
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5.1 Cell division
5.2 What is DNA?
5.3 Cell cycle?
5.4 Mitosis
5.5 Cytokinesis
5.6 Gametes
5.7 Meiosis
5.8 Mitosis vs. meiosis
5.9 Genetic variation
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Chapter 5 Chromosomes and Inheritance:
Unit Hyperlinks
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5.10 Meiosis mistakes
5.11 Mendelian genetics
5.12 Punnett square
5.13 Independent assortment
5.14 Pedigrees
5.15 Complex inheritance
5.16 Linked genes
5.17 Sex-linked genes
5.18 Clones
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5.1 Opening Questions: Cell birth and death
Did you know that between 50 and 70
billion of your cells die each day?
• Is your body making any new cells right
now? What kind?
• Are certain types of cells replaced
faster? What might be examples?
• Are certain types of cells never replaced
or slowly replaced? What might be
examples?
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5.1 All living organisms consist of cells.
• A fundamental concept in
biology is the cell theory,
which states:
1. All life is cellular.
2. All cells arise from
preexisting cells.
Some living organisms
have just one cell, but
others have trillions.
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5.1 Cell division is the formation of new
cells from preexisting cells
Cell division provides for
1. Growth
2. Repair
3. Reproduction
Organisms can use cell
division to reproduce
sexually or asexually.
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5.1 Sexual reproduction takes two parents
• Two parents produce
genetically unique
offspring.
• Gametes (egg and
sperm cells) are
formed via cell
division from adult
cells in the gonads
(testes and ovaries).
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5.1 Life cycle in sexual reproduction:
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5.1 Asexual reproduction only needs one
parent
• One parent produces
genetically identical
offspring.
• There is no sperm or egg
involved.
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5.1 Sexual vs. asexual reproduction
Complete the comparison table:
Sexual
Number of parents needed
Gametes? (yes/no)
Fertilization? (yes/no)
Number of chromosome sets
Offspring genetically unique?
(yes/no)
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Asexual
5.1 Sexual vs. asexual reproduction
Sexual
Asexual
Number of parents needed
2
1
Gametes? (yes/no)
YES
NO
Fertilization? (yes/no)
YES
NO
Number of chromosome sets
2
1
Offspring genetically unique?
(yes/no)
YES
NO
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5.2 Opening Questions: What is DNA?
• What type of information is stored in DNA?
• How different is your DNA from the person
sitting next to you?
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5.2 Opening Questions: What is DNA?
• What type of information is stored in DNA?
• How different is your DNA from the person
sitting next to you?
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5.2 DNA and genes:
• All life on Earth uses DNA
as the genetic material.
• The nucleus of every
eukaryotic cell contains long
strands of DNA called
chromosomes.
• Each chromosome contains
genetic information in
genes.
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5.2 DNA and genes:
• A gene is a length of DNA
that codes for the proteins
that make up our bodies.
Genes are the unit
of inheritance.
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5.2 A closer look at the chromosome
• Inside the nucleus,
the chromosomal
DNA is wound
around proteins;
together they form
chromatin.
Most of the time
chromosomes are
unraveled as loose
chromatin.
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550,000x
11,000x
450x
5.2 Chromosome number: every human
body cell has 46 chromosomes
How many
chromosomes
did you inherit
from your
mother?
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5.2 Chromosomes at cell division have
unique properties
At cell division
chromosomes
1. Become tightly
packed
2. Duplicate
Pairs of duplicated chromosomes
are called sister chromatids.
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5.2 Chromosomes duplicate prior to division
• Sister chromatids
(duplicated
chromosome pair)
are joined at the
centromere.
Formation of sister
chromatids means the
cell is preparing to divide.
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5.3 Opening Questions: Cell cycle
• Healthy cells only start dividing if there
is a need for replication.
Provide at least three examples of times
when a cell (animal, plant, protist) would
need to go through cell division.
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5.3 Opening Questions: Cell cycle
• Unhealthy cells may undergo
unregulated cell division.
• Cancer begins when a cell divides
although it should not.
What are some things you know about
cancer?
Why might cancer be so difficult to treat?
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5.3 Cells have regular cycles of growth and
division
• The cell cycle is an ordered sequence of
events in the “lifetime” of a cell.
• There are two broad phases:
1. Interphase
90% of cell’s lifetime
Normal cell functions
2. Mitotic phase
Active cell division
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5.3 The cell cycle:
Healthy cells
only enter the
mitotic phase
if duplication
is needed.
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5.3 Most of a cell’s lifetime is spent in
interphase
During interphase, the cell
• Performs its normal functions
• Grows
• Prepares for division by duplicating its
chromosomes
What are some normal
functions of cells?
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5.3 Active cell division is the mitotic phase
During the mitotic phase, the cell
• Undergoes active division (mitosis)
• Splits into two offspring cells
(cytokinesis)
The result of the mitotic
phase is two genetically
identical offspring cells.
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5.4 Opening Questions: Mitosis puzzle
The cells below are all undergoing the
process of cell division.
A
B
C
D
Think about what is happening in the cell
during division, and try putting them in
logical order from start to finish. Explain
your choices.
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5.4 Mitosis is active cell division
Mitosis occurs in major stages.
• These stages help us think about how the
chromosomes are organized during
mitosis.
• However, cell division proceeds
seamlessly through all the stages.
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5.4 Interphase:
1. Early interphase
Cell is carrying out
its normal activities.
2. Chromosomes
duplicate
Cell is preparing to
divide; generates
sister chromatids.
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5.4 Stages of mitosis
3. Chromosomes
condense
Nuclear membrane
dissolves. Cell lays down
mitotic spindle.
4. Chromosomes align
Sister chromatids line
up and attach to mitotic
spindle.
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5.4 Stages of mitosis
5. Chromosomes
split
Sister chromatids are
pulled apart as mitotic
spindle retracts.
6. Nucleus reforms
Two duplicated nuclei
are formed.
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5.5 Cytokinesis is the final step in cell
division
• Cytokinesis is the
division of the
cytoplasm and is
the final step in the
cell cycle.
• The process of
cytokinesis is
different for plant
and animal cells
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5.5 Cytokinesis in animal cells:
• The parent animal cell is pinched into two,
leaving two independent offspring cells.
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5.5 Cytokinesis in plant cells:
• Plant cells divide their cytoplasm
by forming a cell plate
along the center
line of the cell.
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5.5 Review Questions:
Many chemotherapy drugs are used to treat
cancer by killing cells undergoing mitosis.
• What side effects have you heard of related
to chemotherapy treatment for cancer?
• With your understanding of mitosis, can
you explain some of the side effects of
chemotherapy?
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5.6 Opening Questions: How do you get one
from two?
• Most of the cells in your
body are diploid; they
have two copies of each
chromosome.
If your cells are diploid, how
could you reproduce without
doubling the chromosome
number in your offspring?
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5.6 Gametes are the answer!
• To prevent doubling
chromosome number
in offspring, sexually
reproducing organisms
need to make cells with a
single set of chromosomes.
• Gametes, or sex cells,
are haploid: they contain
only one copy of each
chromosome.
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5.6 Male and female gametes:
• Male gametes are called sperm.
• Female gametes are called eggs.
How many
chromosomes
are there in a
human sperm
cell?
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5.6 The human life cycle:
ADULTS
Every somatic cell in
your body is diploid,
with one set of
chromosomes derived
from your mother and
one from your father.
DEVELOPMENT
Through repeated
rounds of cell division, the
original zygote cell is duplicated,
eventually forming an embryo,
then a baby, and finally an adult.
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GAMETE FORMATION
In the adult gonads (testes in
males and ovaries in females),
a special kind of cell division
produces gametes. The male
gamete is the sperm and the
female gamete is the egg. As
the only haploid cells in your
body, gametes can be used
to form the next generation.
During fertilization, the
gametes (male sperm
and female egg) fuse.
Each contributes a
haploid number of
chromosomes to produce
a diploid zygote.
ZYGOTE
The zygote, or fertilized egg,
is the original cell that was
formed by the fusion of sperm
and egg. The zygote contains
one haploid set of chromosomes from the father and
one haploid set of chromosomes from the mother that
together make a unique
diploid set of chromosomes.
5.6 One pair of chromosomes makes you
male or female
• The 46 chromosomes in your body are
organized as 23 homologous pairs.
• Of these, 22 pairs are autosomes.
• One pair is your sex chromosomes.
– Females are XX.
– Males are XY.
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5.6 Karyotypes are photographic inventories
of chromosomes
• Chromosomes are
organized in
homologous
pairs.
Can you tell if this a
male or a female?
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5.7 Opening Questions: Why do we need to
produce sperm and eggs (gametes)?
• Explain why all sexually reproducing
organisms need both haploid and diploid
cells.
Remember:
Haploid cells have only one copy of each chromosome.
Diploid cells have two copies of each chromosome.
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5.7 Meiosis is the production of gametes
• Gametes (sperm and egg) are formed by
a special type of cell division, meiosis.
• Cells produced from meiosis are haploid.
• Like mitosis, meiosis occurs in stages.
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5.7 Meiosis occurs in stages
• Meiosis (like mitosis) starts with
chromosome duplication before division.
• In meiosis, there are then two rounds of
cell division.
• The result of meiosis is four haploid
offspring cells, all with one-half the number
of chromosomes.
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5.7 Meiosis interphase
• In meiosis interphase, chromosomes
duplicate.
Remember that
chromosomes
come in
homologous
(matched)
pairs.
• After interphase, cells that are producing
gametes undergo two rounds of division
called meiosis I and meiosis II.
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5.7 Meiosis I:
1. Homologous
chromosome
pairs line up
2. Homologous
pairs separate
3. Cytokinesis
Note that in meiosis I the homologous
pairs line up and separate.
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5.7 Stages of meiosis II:
4. Chromosomes
condense and
line up
5. Chromosomes
separate
6. Cytokinesis II
At the end of meiosis II
there are four haploid
offspring cells.
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5.8 Opening Questions: Meiosis vs. mitosis
Try to complete the comparison table below:
Meiosis
Where does it occur?
When is it needed?
How many/type offspring cells?
(haploid/diploid)
How many rounds of cell
divisions?
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Mitosis
5.8 Mitosis and meiosis compared
Meiosis
Mitosis
Where does it occur?
Ovaries/
testes
All body
cells
When is it needed?
Puberty
Lifetime
How many/type offspring cells?
(haploid/diploid)
How many rounds of cell
divisions?
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4 haploid 2 diploid
2
1
5.8 Study aids:
• Come up with some study aids to help you
remember when the body needs to use
meiosis versus mitosis.
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5.9 Opening Questions: How unique are
you?
• What is the probability that another human
on earth shares the exact same DNA as
you?
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5.9 Opening Questions: How unique are
you?
• What is the probability that another human
on earth shares the exact same DNA as
you?
Unless you have an identical twin,
you are genetically different from
any human that has every lived!
How is that possible?!
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5.9 Sexual reproduction leads to variation
Three major processes mean variation is
the norm for sexual reproduction:
1. Independent assortment
2. Random fertilization
3. Crossing over
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5.9 Independent assortment of
chromosomes leads to variation
• Chromosomes line
up by homologous
pairs during meiosis I.
• Maternal and paternal
chromosomes are
shuffled randomly.
Independent assortment:
223 = 8 million possible
arrangements of
chromosomes!
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Chromosomes
are shuffled
5.9 Random fertilization by sperm and egg
leads to variation
• The probability that
any one sperm will
fertilize any
particular egg is
extremely small.
Random fertilization:
8 million x 8 million =
64 trillion possible
arrangements of
chromosomes.
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Chromosomes
are shuffled
5.9 Crossing over during meiosis leads to
variation
• Chromosomes can
“swap” genetic
material, creating new,
unique combinations.
• Crossing over occurs
when homologous
chromosomes line up
during meiosis I.
Crossing over creates new hybrid chromosomes,
which increases gene variation.
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5.10 Opening Questions: What if meiosis
goes wrong?
• Jason and Laura are pregnant with their
third child. Since they are both over 35,
they opt to have an amniocentesis test.
The doctor comes back to them with a
karyotype that shows 47 chromosomes.
Imagine you are Jason and Laura’s
genetic counselor. How would you
explain the results?
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5.10 Meiosis can have mishaps!
• Non-disjunction is when
chromosomes fail to
separate properly.
• Resulting gametes will
have too few or too many
chromosomes.
Zygotes with abnormal chromosome number will
usually not develop or will have abnormalities.
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5.10 Examples of nondisjunction
• Trisomy 21 is a
condition in which
a person receives
three copies of
chromosome 21.
• The resulting
condition is called
Down syndrome.
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5.10 Examples of nondisjunction
• Sex chromosome
nondisjunction can
also occur.
• Each combination
of extra or missing
sex chromosomes
produces its own
syndromes.
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5.10 Examples of nondisjunction
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5.11 Opening Questions: Did you inherit
your good looks?
• Why do children resemble their parents?
• Why do families resemble each other?
• Is there anything you can’t inherit from
your parents?
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5.11 Our understanding of genetics starts
with Mendel
• Heredity is the transmission
of traits from one generation
to the next.
• Genetics is the study of
heredity.
• Gregor Mendel was the first
to deduce the basic
principles of inheritance.
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5.11 Character and traits are inherited
• Human eye color is a
character, or an inherited
feature that varies among
individuals.
• Each possible variation of
a character is a trait.
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5.11 Alleles are the individual units of
inheritance
• Traits derive from genes.
• Alternate forms of a particular gene are
called alleles.
Matched set of
chromosomes,
one derived
from the father
(blue) and one
derived from the
mother (red)
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5.11 Genotype vs. phenotype
• An organism’s
phenotype is its
physical traits.
• An organism’s
genotype is its
underlying genetic
make-up, the
alleles it is
carrying.
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5.11 Dominant vs. recessive alleles
• An individual who is
heterozygous has two
different alleles.
• Only one allele will
usually determine an
organism’s appearance.
In pea plants, purple (P) is
the dominant trait for flower
color. White (p) is the
recessive trait.
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5.12 Opening Questions: Can we predict the
inheritance patterns of genes?
• For some people the chemical PTC
(phenylthiocarbamide) tastes very bitter;
yet for others, it is tasteless. Scientists
report that the ability to taste PTC shows a
general pattern of dominant inheritance
(T and t).
What is the genotype of a non-taster?
Could a non-taster’s parents be tasters?
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5.12 A Punnett square can be used to
predict the results of a genetic cross
• In a genetic cross, two parents
(P generation) are crossed to
produce offspring (F1 generation).
×
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A Punnett square
can be used to
predict the offspring
that will result from a
genetic cross.
5.12 Punnett squares are predictions
• Punnett squares are named after a British
geneticist: Reginald Punnett.
• A Punnett square allows you to predict the
genotype and phenotype of the offspring.
• The simplest Punnett
square follows one
character in a
monohybrid cross.
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5.12 Punnett square: Monohybrid cross
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5.12 Alleles separate during meiosis
• The law of segregation states that the
two alleles for a character separate during
gamete formation.
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5.12 We can use a test cross to determine
an individual’s genotype
Is the genotype
of this black Lab
BB or Bb? To find
out, mate it with
a chocolate Lab.
×
Chocolate Lab
with genotype bb
For the test cross above, predict offspring
ratios for each possible genotype.
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5.12 Test cross results if black dog is BB:
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5.12 Test cross results if black dog is Bb:
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5.13 Opening Questions: Can we look at
more than one trait?
• In Labrador retrievers, breeders need to
keep track of traits for coat color (black is
dominant to chocolate) and hearing
(normal is dominant to deafness).
If you want all chocolate
coats, how would you
avoid breeding deaf
puppies?
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5.13 Alleles separate independently during
gamete formation
• The law of independent assortment
states that the inheritance of one character
has no effect on the inheritance of
another.
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5.13 Traits for coat color and hearing are an
example of independent assortment
All four kinds
of gametes are
equally likely
to be produced.
Genotype: BbDd
Phenotype: black
coat, hearing
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5.13 Independent assortment can be
observed during a dihybrid cross
• A dihybrid cross is one in which two
separate characters are studied.
MALE
Phenotype:
black coat
hearing
Genotype:
BbDd
×
FEMALE
Phenotype:
black coat
hearing
Genotype:
BbDd
What are the possible allele
combinations for the gametes?
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5.13 Dihybrid cross:
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5.14 Opening Questions: Can
understanding inheritance help us
understand disease?
• Katie and Dave are a healthy young
couple, but both have a sibling with cystic
fibrosis (a recessive disorder). Genetic
tests reveal they are both heterozygous.
They want to know their risk of having a
child with cystic fibrosis.
If you were their genetic counselor, how
would you explain the risks?
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5.14 Some human genetic characters are
controlled by one gene
• For example, the freckled phenotype is
dominant to the non-freckled phenotype.
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5.14 Many human genetic disorders are
recessive
• A carrier is a
heterozygous
individual.
• Carriers do not
have the disease,
but they can pass it
on to offspring.
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5.14 Pedigrees can be used to track genetic
traits in a family
Grandma and
grandpa had two
daughters, one of
whom married and
had four kids.
This daughter
does not have
the trait, but we
cannot tell if
she is Aa or AA.
This daughter has
the trait and
therefore must be
aa, having inherited
the recessive allele
from each parent.
This child has the trait, which is
how we know her father was a carrier
(she could not have inherited two
recessive alleles from her mother.)
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Because they produced a daughter
with the trait but don’t have it themselves,
both grandparents must be carriers.
Because this man
has a daughter with
the trait but does
not have the trait
himself, he must be
a carrier.
These three children must have received one a recessive
allele from their affected mother, but they don’t have
the trait. So they must be carriers themselves.
5.15 Opening Questions: Can we always
count on Mendel’s laws?
• Farmers have long observed that crossing
cattle with red and white coats results in
offspring with a roan color (intermediate
color).
If coat color is a single gene with two
alleles (R and r), does the roan color make
sense according to Mendel’s laws?
If not, how would you explain it?
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5.15 Genetic inheritance has complexities
• Not all genes follow a
classic Mendelian
inheritance pattern.
• We often encounter
patterns that are
more complex.
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5.15 Sometimes both alleles are expressed
• For some genes there is a
pattern of incomplete
dominance.
• Individuals that are
heterozygous will have a
phenotype intermediate in
appearance.
Remember: in classic Mendelian genetics,
heterozygous individuals have the appearance
(phenotype) of the dominant gene.
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5.15 Flower color in snapdragons is a trait
with incomplete dominance
• Heterozygous
individuals show an
intermediate trait.
Now use a Punnett
square to predict the
outcome of Rr × Rr
for snapdragons.
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5.15 A cross between two pink snapdragons
exemplifies incomplete dominance
Only RR individuals
have a red phenotype.
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5.15 For most traits there are multiple alleles
• Classic Mendelian genetics only uses two
allele copies (such as R and r).
• Most genes actually have multiple alleles.
For any gene, how
many allele copies can
one person carry?
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Education,
Inc.
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5.15 Blood types in humans are the result of
multiple alleles
• Human blood types are
determined by a gene
with three alleles:
i, IA, IB.
• These three alleles can
be combined in six
ways.
Alleles for blood type are also codominant, which
means both are expressed.
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5.15 Parents with different blood types
exemplify multiple alleles and codominance
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5.15 Genes may have multiple effects
• In some cases, one gene influences many
characters, a situation called pleiotropy.
• The sickle-cell mutation can cause many
physical changes.
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5.15 Many phenotypic characters are the
result of many genes
• Polygenic inheritance is the effect of
many genes on a single character.
• In humans, height and skin color are each
affected by several genes.
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5.15 Many genes have both a genetic and
environmental component
• Some traits are entirely genetic, some are
a mix of environment and genetics, and
some traits are just environmental.
Only genetic influences are inherited!
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5.16 Opening Questions: What if traits are
on the same chromosome?
• So far, we have assumed that traits are on
different chromosomes.
• But what if they are on the same
chromosome? Will they still segregate
independently?
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5.16 Not all genes obey Mendel’s law of
independent assortment
• Linked genes are
located close
together on the same
chromosome and
tend to be inherited
together.
Linked genes display
different offspring
ratios compared to
unlinked genes.
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5.16 Crossing over is less likely to occur
for closely located genes
• Crossing over produces new hybrid
recombinant chromosomes.
• Genes located very near each other have
little chance of a crossover.
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5.17 Opening Questions: What if traits are
on the sex chromosomes?
• So far, we have assumed that traits are on
autosomes.
• But what if they are on the sex
chromosome (X or Y)?
• How might patterns of inheritance differ?
• What if there is a genetic disease just on
the X chromosome? What about
phenotype?
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5.17 Sex-linked genes are those carried on
the sex chromosomes
• Human cells contain 44 autosomes and
2 sex chromosomes:
XX = Female XY = Male
• Because females have
two X chromosomes
while males have only
one, sex-linked gene
display unusual
inheritance patterns.
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5.17 Hemophilia is a recessive mutation
carried on the X chromosome
• A single copy of the normal (dominant)
gene will prevent the disease.
• Men have a single X chromosome, so a
male carrier of the hemophilia gene will
have the disorder.
• In the last Russian
royal family, the son
had hemophilia,
which he inherited
from his mother.
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5.18 Opening Questions: Can science
harness cell division?
• In 2004, a company called Genetic Savings
& Clone produced the first commercially
cloned pet, a cat named Little Nicky (for a
fee of $50,000).
Would you clone your pet?
What are some other possible
scientific uses of cloning?
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5.18 Nuclear transfer can be used to
produce clones
• Biologists can artificially manipulate cell
division to produce clones.
– Clones are genetically identical individuals
born of a single parent.
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5.18 Cloning can be done through the
process of nuclear transplantation
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5.18 Cloned embryos can be used to
produce a new individual
• In reproductive cloning the embryo must
be transplanted into a surrogate.
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5.18 Cloned embryos can be used to
produce stem cells
• In therapeutic cloning, stem cells are
harvested from the cloned embryo.
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