Download Medical Genetics

Mendelian Inheritance
... the outward physical
manifestation of
internally coded,
inheritable, information.
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Genetics vs Heredity?
Genetics: the branch of biology that
studies heredity
Heredity: the passing of
characteristics (or traits) from
parents to offspring
2
Gregor Mendel
 Father of
Genetics
 1823-1884
 Monk in
Austria/Czech
Republic
 Experimented
with garden peas
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Mendel…Why do you think?
His experiments were successful?
He used peas?
He controlled his experiments?
How did he do it?
Why would his profession be
beneficial?
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Tall
Short
Tall
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Mendel’s 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
T
t
Tt
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TT
TT
T
T
TT
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tt
tt
t
t
tt
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A Monohybrid cross..
What’s the answer?
The original parents differ by what?
The original parents are called the?
Their offspring are called what (the
kids)?
And their offspring are called what
(the grandkids)?
10
Discovery of Chromosomes in
1900 Confirms Law of
Segregation
 Chromosomes
are in pairs
 Each
chromosome
has one of the
allele pairs for
each trait
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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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Meiosis Metaphase
Chromosomes line up in a
double row.
T T
t t
Assume a T allele on each red chromatid and a t
allele on each blue chromatid
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Chromosomes separate
Each each daughter cell gets
doubled chromosomes
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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Mendel’s Law of
Dominance
Dominant alleles are expressed
Recessive alleles are not
expressed in the presence of a
dominant allele
– Recessive alleles are only expressed
if both 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
My genes are
Tommy genes!
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Keeping Up Quick Check:
What is the relationship between
DNA & genes & homologs ^
homolgous chromosomes?
Can you draw a picture?
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Homozygous
Both alleles alike
AA or aa
A A
a
a
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Heterozygous
Alleles are different
Aa
A a
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Law of Segregation
Mendel’s
Gametes have 1 allele for each trait
2 alleles for each trait separate
during meiosis During fertilization,
the alleles for that trait reunite.
This happens at random to create
individuals of the next generation.
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Genotype
Genetic make up
Represented by alleles
TT & Tt are genotypes for tall pea
plants
This is the
"internally coded,
inheritable
information" carried
by all living
organisms.
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Phenotype
The
characteristic
Genotype
determines the
phenotype
Tall is a
phenotype
“Think
adjective!”
Descriptive
This is the "outward,
physical manifestation"
of the organism.
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A flower….
 Phenotype: red
flowers
 Cells contain red
granules &
enzymes help
convert colorless
pigment into red
pigment
 Most enzymes
are proteins
 Most traits are
produced by the
action of proteins.
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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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a
A
Amino Acids
Enzyme
Melanin Pigment
AA = Normal
pigmentation
Aa = Normal
pigmentation
aa = Albino
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PKU Disease
 Phenylalanine
excess
 Mental
retardation if
untreated
Molly’s Story
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p
P
Phenylalanine
Enzyme
Tyrosine
PP = Normal
Pp = Normal
pp = PKU
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A man & woman are both carriers
(heterozygous) for albinism. What
is the chance their children will
inherit albinism?
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AA = Normal
pigmentation
Aa = Normal
pigmentation
(carrier)
Man = Aa
Woman = Aa
aa = Albino
A
A
a
a
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A
a
A
AA
Aa
a
Aa
aa
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Genotypes
1 AA, 2Aa, 1aa
Phenotypes
AA
Aa
3 Normal
1 Abino
Aa
aa
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?
37
PP = Normal
Pp = Normal
(carrier)
pp = PKU disease
P
p
PP
Pp
Pp
pp
P
p
38
Genotypes
1 PP, 2Pp, 1pp
Phenotypes
3 Normal
PP
Pp
1 PKU disease
Probability
Pp
pp
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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SS = Normal
Ss = Normal
(carrier)
ss = Sickle Cell
S
s
s
Ss
ss
s
Ss
ss
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Genotypes
2 Ss, 2ss
Ss
ss
Phenotypes
2 Normal (carriers)
2 Sickle cell
Ss
ss
Probability
50% for Sickle cell
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Dwarfism
 Oddly a dominant
trait
Dwarfism = D
Normal height = d
DD = Dwarfism
Dd = Dwarfism
Dwarf Band
dd = Normal height
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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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DD = Dwarf
Dd = Dwarf
dd = Normal
d
d
D
Dd
Dd
d
dd
dd
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Genotypes
2 Dd, 2dd
Phenotypes
2 Normal
2 Dwarfs
Dd
Dd
Probability
50% for Dwarfism
dd
dd
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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
The random distribution of alleles
occurs gamete formation & genes
on chromosomes sort
independently during meiosis
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A Dihybrid Cross
A heterozygous tall plant that is
also heterozygous for yellow
seeds self pollinates.
Tall and yellow seeds are
dominant to short and green
seeds.
What are the genotypes &
phenotypes of the offspring in
fractions?
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What gametes can each parent produce?
Tall Yellow
Tall Yellow
TtYy
TtYy
TY
Ty
tY
ty
TY
Ty
tY
ty
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Match gametes on a Punnent Square
TY
Ty
tY
ty
TY TTYY
TTYy
TtYY
TtYy
9 Tall-Yellow
Ty
TTYy
TTyy
TtYy
Ttyy
3 Tall-Green
tY
TtYY
TtYy
ttYY
ttYy
3 Short-Yellow
ty
TtYy
Ttyy
ttYy
ttyy
1 Short-Green
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A man with blue eyes and normal
height marries a woman with
heterozygous brown eyes and
homozygous dwarfism. What are
the possible phenotypes of their
children? Dwarfism & brown eyes
are dominant. (Calculate in % &
ratios)
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What gametes can each parent produce?
Normal height-Blue
Dwarf-Brown
ddbb
DDBb
db
DB
Db
DB
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The Answers:
Dwarf-Brown eyes
Dwarf-blue eyes
Normal height-Brown eyes
Normal height-Blue eyes
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The End of Mendlian Genetics
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Pedigree
 Shows
relationships
 Used to determine
inheritance
patterns
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Pedigree Symbols
Female
Male
Person has a trait
Parents
Parents closely related
Parents
Children
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Dominant Pedigree
 Affected individual
must have a
parent with the
trait
57
Genotypes
AA
Aa
aa
Could have either genotype
aa
aa
Aa
aa
aa
aa
Aa
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Recessive Pedigree
 May appear
when neither
parent has the
trait
 If both parents
have the trait,
all the children
will inherit it
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Genotypes
Aa
Aa
aa
Aa
AA
aa
Aa
Aa
aa
Aa
AA
aa
aa
aa
aa
aa
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Is this a dominant or recessive
pedigree?
Click for answer
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Recessive pedigree
Recessive because it appears in individuals
when their parents do not have the trait.
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Give genotypes for marked
individuals
Click for answer
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Genotypes
aa
Aa
AA or Aa
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Is pedigree dominant or recessive?
Click for answer
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Dominant pedigree
Dominant because all affected individuals inherited
trait from a parent
66
Give genotypes for marked individuals
Click for answer
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Give genotypes for marked individuals
Aa
aa
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The End
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