Gregor Mendel

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• Gregor Mendel
• Father of Genetics
• Wrote Experiments in
• Plant Hybridization in 1865
• His work wasnt discovered
• until the next century

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Painting of Mendel
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Mendel
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Table 14.1 The Results of Mendels F1 Crosses
for Seven Characters in Pea Plants
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Sweet Pea Flowers
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Alleles, Alternative Versions of a Gene
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Homozygous means having only one form of gene or
allele Ex WW or ww
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Heterozygous means a trait represented by at
least two different alleles, or forms of a
gene Ex Ww
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In the formation of a zygote, or fertilized egg,
each parent of an organism contributes one form
of a gene or allele, for each trait in most
cases.
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In Mendelian Genetics, dominant traits are
represented by capital letters recessive
ones by lower case letters
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Dominant traits (genes) are always expressed if
the gene is present recessive traits are
expressed only if the dominant genes are absent
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For example, widows peak (W) is a dominant trait
in humans. If the gene for widows peak is
present, W, the person will have widows Peak.
(WW, Ww)
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Homologous Chromosomes
This person would have brown eyes (Bb)
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Meiosis - eye color
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The physical appearance of an organism is known
as the phenotype the genetic makeup (the
letters) are known as the genotype Ex Widows
peak is the pheno- type Ww is the genotype
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The way to show the pos- sible pairings of genes
between two organisms is called a Punnett Square.
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Punnett Square

• A Punnett square is used to show the possible
  combinations of gametes.

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Breed the P generation

• tall (TT) vs. dwarf (tt) pea plants

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tall (TT) vs. dwarf (tt) pea plants
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Breed the F1 generation

• Heterozygous Tall (Tt) pea plants

T t
T
t
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Cross a purebred black guinea pig and a
purebred brown guinea pig. Black is
dominant over brown.
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B B
(black)
Bb
Bb
b
All offspringare black and heterozygous.
Bb
Bb
b
(Brown)
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If bushy eyebrows (B) are dominant over fine
eyebrows, (b), show the cross between one parent
heterozygous for the trait and one who is
homozygous recessive.
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What are the phenotypes and genotypes of the
offspring? Answer Bushy (Bb) 50 and
fine (bb) 50
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Monohybrid Cross

• A breeding experiment that tracks the inheritance
  of a single trait.

Dihybrid Cross

• A breeding experiment that tracks
• the inheritance of two traits.

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Mendels principle of segregation a. pairs of
genes on homologous chromosomes separate during
gamete formation (meiosis) and end up in
different gametes. b. the fusion of gametes at
fertilization pairs genes once again. Ex The
alleles for height in Mendels pea plants end up
in separate gametes. Tt X Tt could yield four
the offspring TT, Tt, Tt, tt.
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Meiosis - eye color
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Mendels Law of Segregation
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• Mendels principle of independent assortment
  (2 different genes)
• a. each pair of alleles on nonhomologous
  chromosomes segregates independently of other
  pairs during gamete formation
• Ex When Mendel crossed F1 plants that were
  heterozygous for
• round yellow peas, some F2 plants
• did not resemble the parent plants.

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Independent Assortment

• How many different gametes can be produced for
  the following allele arrangements?
• Remember 2n (n of heterozygotes)
• 1. RrYy
• 2. AaBbCCDd
• 3. MmNnOoPPQQRrssTtUu

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Answers
1. RrYy 2n 22 4 gametes RY Ry rY
ry 2. AaBbCCDd 2n 23 8 gametes ABCD ABCd
AbCD AbCd aBCD aBCd abCD abCD 3.
MmNnOoPPQQRrssTtUu 2n 26 64 gametes
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Autosomal Inherited Traits are inherited via the
autosomes (non-sex) chromosomes. How many
autosomes are in each of your somatic cells?
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Thats right! There are 44 autosomes and 2 sex
chro- mosomes in each of your somatic (non-sex)
cells.
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Figure 13.x5 Human male karyotype shown by
bright field G-banding of chromosomes
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• Autosomal Inherited
• Genetic Disorders
• include
• Cystic Fibrosis
• Tay-Sachs Disease
• Sickle Cell Anemia
• Huntington Disease (this
• one is dominant!)

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Testing a Fetus for Genetic Disorders
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• Cystic Fibrosis
• Most common inherited fatal disorder in the U.S.
• Median age of death37
• One in every 29 Americans has the gene
• Mucus builds up in the lungs

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Francis Collins, current director of the National
Human Genome Research Institute (NHGRI) helped
pioneer the discovery of the CF gene in 1989.
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Francis Collins, discoverer of the Cystic
Fibrosis Gene
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Former NFL Quarterback, Boomer Esiason and his
son, Gunnar, who has CF.
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DiagnosisTreatment
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If a man who does not have Cystic Fibrosis has a
sister who died of CF. He marries a woman who
does not have the disease or any history of it in
her family, what is the probability that they
will have kids with the disease?
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Tay Sachs Diseasea lipid-digesting enzyme
is defective in lysosomes
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If two parents are each carriers of the gene for
Tay-Sachs Disease, what is the probability of
them having a child with the disease?
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Thats right! They have a 25 chance!
t
T
Tt
TT
T
Homozygous Dominant
Heterozygous
tt
Tt
t
Homozygous Recessive
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Sickle Cell Anemia
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The molecular basis of sickle-cell disease a
point mutation
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• Huntington Disease
• A degenerative disorder
• of the nervous system
• Most people dont realize that they have the
  disease until after age 30
• and may have passed on the gene

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Lake Maracaibo, Venezuela
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Nancy Wexlers Pedigree of 10,000 people in Lake
Maracaibo
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Huntington Disease (chorea)
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• Caused by a stuttering
• gene - CAG repeat
• Also called Huntingtons
• Chorea
• This is a dominant gene

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Some human traits are sex-linked that is
they are carried on the X and Y Chromosomes
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For Example Hemophilia, Duchenne Muscular
Dystrophy, and Colorblindness are all
traits carried on the X chromo- some
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Hemophilia
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Colorblindness
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Duchenne Muscular Dystrophy
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If a female who is carrier for Duchenne
Muscular Dystrophy (D), what is the probability
of she and hernormalhusband having a child
with MD?
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D
d
X X
D
D d
D D
X
X X
X X
Normal
Carrier Female
D
d
Y
X Y
X Y
Male with Disease
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A pedigree shows the genetic relationship between
organisms or people.
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• Bloodtypes are also
• inherited
• A has antigen A
• B has antigen B
• O neither
• AB has both antigens
• A and B

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Genotypes O OO AB AB A AA or AO
(codominance) B BB or BO (codominance)
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Alleles and Genes Interact to Produce Phenotypes

• Codominancetwo alleles of a gene produce
  phenotypes that are both present in the
  heterozygote.
• Example ABO blood group system has three alleles
  of the gene IA, IB, and IO.

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ABO Blood Reactions Are Important in Transfusions
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O is the universal donor (can donate blood to
anyone) AB is the universal recipient ( can
receive blood from anyone)
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• Patient Donor
• A A or O
• B B or O
• AB anyone
• O O
• a person who is Rh negative for any blood type
  must take only Rh negative blood

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The Rh Factor is also inherited. Approximately
85 of Americans are positive for the Rh Factor.
For example, if you have type A blood and are
positive for the Rh Factor then your bloodtype is
A positive.
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So technically there are 8 blood groups A
positive AB positive A negative AB negative B
positive O positive B negative O negative
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In terms of a couple having kids, positive blood
dominates negative blood. For example, a father
with A positive blood and his wife with A
negative blood would have kids with A positive
blood.
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RhoGAM A woman who is pregnant and is Rh
negative and has an Rh positive child must take
RhoGAM in order to not reject the child.
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If a woman who is type O and a man who is type
A have kids, what are their possible bloodtypes?
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O O
WOMAN
AO
AO
A
MAN
AO
AO
A
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A O
O
AO
OO

AO
O
OO
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1) If a brown eyed man marries a brown eyed woman
and they have a blue eyed child, what are the
genotypes of the parents?
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2) In rabbits, the allele for black coat color
(B) is dominant over the allele for brown coat
color (b). Predict the results of a cross
between a rabbit homozygous for black coat color
(BB) and a rabbit homozygous for brown coat color
(bb)
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3) If two sisters in a family have free earlobes
(F) and their two brothers have attached
earlobes (f), what genotypes are the parents
most likely to have if neither parent
has attached earlobes?
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4) What is the probability of a couple who are
both heterozygous for widows peak (W) and free
earlobes (F) having a child with neither trait?
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5) In pea plants, smooth seed texture is
dominant over wrinkled seed texture. A gardener
has a pea plant that produces smooth seeds.
How can the gardener determine whether the
plant is homozygous or heterozygous for the
allele that determines seed texture?
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6) In pea plants, if purple flowers are dominant
over white, and smooth seeds are dominant over
wrinkled, predict the out- come of the crossing
of a pea plant heterozygous for color and
homozygous recessive for seed coat texture with
one heterozygous for both traits.
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7) In fruit flies, L long wings and l short
wings. When a long-winged fly is crossed with a
short-winged fly, the offspring exhibit a 11
ratio. What is the genotype of the parent flies?
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8) In squash an allele for white color (W) is
dominant over yellow (w). Give the phenotypic
ratios for the results of each of the following
crosses a) W/W x w/w b) W/w x w/w c) W/w x
W/w
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9) In humans, pointed eyebrows (B) are dominant
over smooth eyebrows (b). Marys father has
pointed eyebrows, but she and her mother have
smooth. What is the genotype of the father?
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10) In tomatoes, red fruit (R) is dominantover
yellow fruit (r), and tallness (T) is dominant
over shortness (t). A plant that is RrTT is
crossed with aplant that is rrTt. What are the
chances of an offspring beingheterozygous for
both traits?
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11) In fruit flies, gray wings (G) are dominant
to black wings and normal wing length (N) is
dominant to vestigial (short) wing length. What
is the probability of a gray fly with normal
wings heterozygous for both traits and a black
fly with normal wings, but homozygous for wing
length having offspring which are gray and have
normal wing lengths?
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12) Free ear lobes (F) and widows peak (W) are
dominant traits in humans. What is the
probability of a woman who has attached earlobes
and no widows peak and a man who is heterozygous
for both traits having kids who have attached
ear lobes and no widows peak?
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Genes A and B are 6 map units apart, and A and C
are 4 map units apart. Which gene is in the
middle if B and C are 10 map units apart? Which
is in the middle if B and C are 2 map units apart?
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• In the cross RrTt X rrtt,
• all of the offspring will be tall with red
  fruit
• b. 75 will be tall with red fruit
• c. 50 will be tall with red fruit
• d. 25 will be tall with red fruit

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In terms of evolution, why is the incidence of
sickle cell anemia higher among the
African-American population in the United States?
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If one parent has type O blood and one of the
kids is type A, what are the possible blood
types of the other parent? If one parent has
type AB blood and the other has A, what are the
possible blood types of the kids?
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For most human traits, how many alleles does each
parent contribute to the zygote or fertilized
egg? What is the term used to describe traits
that are inherited by a number of genes of each
parent?
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• If you have good notes from yesterday
• on Cystic Fibrosis you should be able to
• describe at least two organs affected
• show a Punnett square with the
• inheritance pattern
• 3) list one organization which raises
• awareness of CF
• 4) name and describe the specific protein
  affected by CF
• 5) significance of discovery of the CF gene

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When RhoGAM is given to a pregnant mother, what
is the Rh status of the mother, father, and
baby?