Mendelian Inheritance Part 1

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Mendelian InheritancePart 1

• BIO 2215
• Oklahoma City Community College

Dennis Anderson
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Gregor Mendel

• Father of Genetics
• 1823-1884
• Monk in Austria
• Experimented with garden peas

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Tall
Short
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Mendels Hypotheses

• Each parent has two factors (alleles)
• Each parent gives one of those factors to the
  offspring
• Tall has TT
• Short has tt
• Tall is dominant
• Short is recessive

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TT
tt
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TT
TT
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tt
tt
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Law of Segregation

• Alleles separate during gamete production
• Gametes have one allele for each trait
• During fertilization gametes combine at random to
  form individuals of the next generation

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Discovery of Chromosomes in 1900 Confirmed Law of
Segregation

• Chromosomes are in pairs
• Each chromosome has one of the allele pair

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T
T
t
t
Assume a T allele on each red chromatid and a t
allele on each blue chromatid
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t
t
T
T
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Doubled Chromosomes Separate in Second Meiotic
Division
T
T
t
t
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Each gamete will have a T allele or a t allele
T
T
t
t
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Allele

• Member of a paired gene
• One allele comes from each parent
• Represented by a single letter

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Dominant Recessive Alleles

• Dominant alleles are expressed
• Recessive alleles are not expressed in the
  presence of a dominant allele
• Recessive alleles are only expressed if both
  recessive alleles are present

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Gene

• A unit of heredity that controls the development
  of one trait
• Made of DNA
• Most genes are composed of two alleles

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Homozygous

• Both alleles alike
• AA or aa

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Heterozygous

• Alleles are different
• Aa

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Genotype

• Genetic make up
• Represented by alleles
• TT Tt are genotypes for tall pea plants

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Phenotype

• A trait
• Genotype determines the phenotype
• Tall is a phenotype

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Homologous Chromosomes

• Chromosomes of the same pair
• Each homologue will have one allele for a paired
  gene
• Homologous chromosomes pair up during meiosis
• Only one of each homologue will be in each gamete

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Sickle Cell Anemia

• RBCs sickle shaped
• Anemia
• Pain
• Stroke
• Leg ulcers
• Jaundice
• Gall stones
• Spleen, kidney lungs

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Sickle Cell Anemia

• Recessive allele s, codes for hemoglobin S
• Long rod-like molecules
• Stretches RBC into sickle shape
• Homozygous recessive ss, have sickle cell anemia
• Heterozygous Ss, are carriers

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Albinism

• Lack of pigment
• Skin
• Hair
• Eyes

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Enzyme
Amino Acids
Melanin Pigment
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PKU Disease

• Phenylalanine excess
• Mental retardation if untreated

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Enzyme
Phenylalanine
Tyrosine
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A man woman are both carriers (heterozygous)
for albinism. What is the chance their children
will inherit albinism?
Monohybrid Cross or One Trait
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Man Aa
Woman Aa
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Aa
AA
Aa
aa
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Genotypes
1 AA, 2Aa, 1aa
Phenotypes
3 Normal 1 Abino
Probability
25 for albinism
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A man woman are both carriers (heterozygous)
for PKU disease. What is the chance their
children will inherit PKU disease?
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p
P
P
p
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Genotypes
1 PP, 2Pp, 1pp
Phenotypes
3 Normal 1 PKU disease
Probability
25 for PKU disease
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A man with sickle cell anemia marries a woman who
is a carrier. What is the chance their children
will inherit sickle cell anemia?
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s
S
s
s
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Genotypes
2 Ss, 2ss
Phenotypes
2 Normal (carriers) 2 Sickle cell
Probability
50 for Sickle cell
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Dwarfism
Dwarfism D Normal height d
DD Dwarfism Dd Dwarfism dd Normal height
Dwarf Band
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A man with heterozygous dwarfism marries a woman
who has normal height. What is the chance their
children will inherit dwarfism? Dwarfism is
dominant.
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d
d
D
d
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Genotypes
2 Dd, 2dd
Phenotypes
2 Normal 2 Dwarfs
Probability
50 for Dwarfism
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Law of Independent Assortment

• The inheritance of one gene does not influence
  the inheritance of another gene if they are on
  separate chromosomes.
• The gene for albinism does not affect the gene
  for dwarfism

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Dihybrid Cross or Two Traits

• A heterozygous tall plant that is also
  heterozygous for yellow seeds is crossed with
  another plant with the same genotype
• Tall and yellow seeds are dominant to short and
  green seeds.

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What gametes can each parent produce?
Tall Yellow
Tall Yellow
TtYy
TtYy
TY
Ty
tY
ty
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Match gametes on a Punnent Square
1 Short-Green
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A man with blue eyes and normal height marries a
woman with heterozygous brown eyes and
heterozygous dwarfism. What are the possible
phenotypes of their children? Dwarfism brown
eyes are dominant.
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What gametes can each parent produce?
Normal height-Blue
Dwarf-Brown
ddbb
DdBb
db
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Match gametes on Punnent Square
db
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X-linked Traits

• Alleles on the X chromosome
• Women have two alleles
• Men have one allele

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Hemophilia

• Blood clotting impaired
• Recessive allele, h
• carried on X cms
• X-linked recessive trait
• More common in males

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Alleles must be written on X chromosome
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A man with hemophilia marries a normal woman who
is not a carrier. What is the chance their
children will inherit hemophilia? Hemophilia is
X-linked recessive.
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XH
XH
Xh
XH Xh
XH Xh
XHy
XHy
y
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Genotypes
2 XH Xh, 2XHy
Phenotypes
2 Carrier Females 2 Normal Males
Probability
O for Hemophilia
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A normal man marries a normal woman who is a
carrier for hemophilia. What is the chance their
children will inherit hemophilia?
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Xh
XH
XH
y
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Xh
XH
Genotypes
1XH XH, 1 XH Xh, 1XHy, 1 Xhy
XH
XH XH
XH Xh
Phenotypes
2 Normal Females 1 Normal Males 1 Male Hemophiliac
XHy
Xhy
y
Probability
50 for Male Hemophiliac 0 for Female Hemophiliac
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Hypertrichosis

• X-linked dominant
• Similar gene in apes

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The End