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Scheman
Gregor
Mendel
• Austrian Monk, mid- 19th
century.
• Worked with Pea plants.
• 1st to succeed in predicting the
passage of traits from parent to
offspring.
• Utilized Scientific Method with
controlled experimentation.
Both
Stamens and
Carpels
Control cross-pollination
• What genetic principles account for the
passing of traits from parents to offspring?
• The “blending” hypothesis is the idea that
genetic material from the two parents blends
together (like blue and yellow paint blend to
make green)
• The “particulate” hypothesis is the idea that
parents pass on discrete heritable units
(genes)
• Mendel documented a particulate mechanism
through his experiments with garden peas
EXPERIMENT
P Generation
(true-breeding
parents)
F1 Generation
(hybrids)
F2 Generation

Purple
flowers
White
flowers
All plants had
purple flowers
Particulate Hypothesis
Proven (no blending)
705 purple-flowered 224 white-flowered
plants
plants
Mendel’s Key Points
• Hybrid = The offspring of
parents that have different
forms for the same trait.
• Two Factors that control gene
activation for any particular
trait. (Alleles)
• Dominant vs. Recessive
• Law of Segregation
• Law of Independent
Assortment
•What Mendel called a “heritable factor” is what we now call a gene!
• Mitosis and meiosis were first described in
the late 1800s
• The chromosome theory of inheritance
states:
– Mendelian genes have specific loci (positions) on
chromosomes
– Chromosomes undergo segregation and independent
assortment
• The behavior of chromosomes during meiosis
was said to account for Mendel’s laws of
segregation and independent assortment
All F1 plants produce
yellow-round seeds (YyRr)
0.5 mm
F1 Generation
R
R
y
r
Y
LAW OF SEGREGATION
The two alleles for each gene
separate during gamete
formation.
y
r
Y
LAW OF INDEPENDENT
ASSORTMENT Alleles of genes
on nonhomologous
chromosomes assort
independently during gamete
formation.
Meiosis
r
R
Y
y
r
R
Metaphase I
Y
y
1
1
r
R
r
R
Y
y
Anaphase I
Y
y
r
R
Metaphase II
R
r
2
2
Gametes
y
Y
Y
R
R
1
4
YR
r
1
3
4
yr
Y
Y
y
r
y
Y
y
Y
r
r
14
Yr
y
y
R
R
14
yR
3
Punnett Squares
• Technique for
predicting offspring
from one generation to
the next.
• Homozygous vs.
Heterozygous
The Testcross
• How can we tell the genotype of an individual
with the dominant phenotype?
• Such an individual must have one dominant
allele, but the individual could be either
homozygous dominant or heterozygous
• The answer is to carry out a testcross: breeding
the mystery individual with a homozygous
recessive individual
• If any offspring display the recessive
phenotype, the mystery parent must be
heterozygous
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
EXPERIMENT
YYRR
P Generation
yyrr
Gametes YR

F1 Generation
YyRr
Hypothesis of
dependent
assortment
Predictions
yr
Hypothesis of
independent
assortment
Sperm
or
Predicted
offspring of
F2 generation
1/
4
Sperm
1/ YR 1/
2
2 yr
1/
4
1/
2
YR
1/
4
1/
4
Yr
yR
1/
4
yr
YR
YYRR YYRr
YyRR
YyRr
YYRr
YYrr
YyRr
Yyrr
YyRR
YyRr
yyRR
yyRr
YyRr
Yyrr
yyRr
yyrr
YR
YYRR
Eggs
1/
2
YyRr
1/
4
Yr
Eggs
yr
YyRr
3/
4
yyrr
1/
4
yR
1/
4
Phenotypic ratio 3:1
1/
4
yr
9/
16
3/
16
3/
16
1/
16
Phenotypic ratio 9:3:3:1
RESULTS
315
108
101
32
Phenotypic ratio approximately 9:3:3:1
Concept 14.3: Inheritance patterns are often
more complex than predicted by simple
Mendelian genetics
• The relationship between genotype and
phenotype is rarely as simple as in the pea plant
characters Mendel studied
• Many heritable characters are not determined by
only one gene with two alleles
• However, the basic principles of segregation and
independent assortment apply even to more
complex patterns of inheritance
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• Inheritance of characters by a single gene
may deviate from simple Mendelian patterns
in the following situations:
– When alleles are not completely dominant or
recessive
– When a gene has more than two alleles
– When a gene produces multiple phenotypes
Degrees of Dominance
• Complete dominance occurs when
phenotypes of the heterozygote and dominant
homozygote are identical
• In incomplete dominance, the phenotype of
F1 hybrids is somewhere between the
phenotypes of the two parental varieties
• In codominance, two dominant alleles affect
the phenotype in separate, distinguishable
ways
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
P Generation
Red
CRCR
White
CWCW
CR
Gametes
CW
incomplete dominance
Pink
CRCW
F1 Generation
Gametes 1/2 CR
1/
CW
2
Sperm
1/
2
CR
1/
2
CW
F2 Generation
1/
2
CR
Eggs
1/
2
CRCR
CRCW
CRCW
CWCW
CW
Multiple Alleles
• Most genes exist in populations in more than
two allelic forms
• For example, the four phenotypes of the
ABO blood group in humans are determined
by three alleles for the enzyme (I) that
attaches A or B carbohydrates to red blood
cells: IA, IB, and i.
• The enzyme encoded by the IA allele adds the
A carbohydrate, whereas the enzyme encoded
by the IB allele adds the B carbohydrate; the
enzyme encoded by the i allele adds neither
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Blood Typing
Allele
IA
IB
Carbohydrate
A
B
i
none
(a) The three alleles for the ABO blood groups
and their associated carbohydrates
Genotype
Red blood cell
appearance
Phenotype
(blood group)
IAIA or IA i
A
IBIB or IB i
B
IAIB
AB
ii
O
(b) Blood group genotypes and phenotypes
• Most genes have multiple phenotypic effects, a property
called pleiotropy
• For example, pleiotropic alleles are responsible for the
multiple symptoms of certain hereditary diseases, such
as cystic fibrosis and sickle-cell disease
• In epistasis, a gene at one locus alters the phenotypic
expression of a gene at a second locus
• For example, in mice and many other mammals, coat
color depends on two genes
• One gene determines the pigment color (with alleles B
for black and b for brown)
• The other gene (with alleles C for color and c for no
color) determines whether the pigment will be
deposited in the hair
• Quantitative characters are those that vary in the
population along a continuum
• Quantitative variation usually indicates polygenic
inheritance, an additive effect of two or more genes on
a single phenotype
• Skin color in humans is an example of polygenic
inheritance
• A pedigree is a family tree that describes the
interrelationships of parents and children across
generations
• Inheritance patterns of particular traits can be traced and
described using pedigrees
Punnett Square
Practice
Great Punnett Square
Problem Web Site
www.biology.arizona.edu
Go to Mendelian Genetics
Meiosis
• The process of making
gametes (sex cells such as
sperm and egg).
• Purpose = to reduce the
chromosome number in
half!
• 1 Diploid(2N) cell
becomes 4 Haploid(N)
cells.
Human Meiosis
• Spermatogenesis
produces 4 viable
sperm every meiosis.
• Oogenesis produces 1
viable egg every
meiosis and 4 polar
bodies.
• Zygote = fertilized egg
which contains the
standard number of
chromosomes.
46
Zygote
• Most of the time, meiosis occurs flawless.
• However, sometimes, chromosomes, parts
of chromosomes, or specific nucleotides get
messed up!
• Genetic disorders are inherited from the
parents and can be found in the DNA of
every cell.
Nondisjunction
Trisomy 21
• Non disjunction
results when an entire
chromosome does not
separate from its sister
chromosome.
• Thus, both
chromosomes travel
together.
Trisomy 21
Cystic Fibrosis
• Common disorder in
Caucasians.
• Mutation in amino
acids that make up a
specific transport
protein.
• Thick mucus builds up
in respiratory and
digestive systems.
Sickle Cell Anemia & PKU
• Minor changes in the
sequence of
nucleotides can lead to
extreme genetic
disorders.
• Sickle cell anemia
• PKU
Sex-Linked Inheritance
• Some inherited traits
are located on the X
and Y (sex)
chromosomes.
• Hemophilia
• Pattern baldness
• Color blindness
• Duchenne muscular
dystrophy
Dominant Inheritance
• 6-Fingers
• Huntington’s Disease
Morgan’s Experimental Evidence:
Scientific Inquiry
• The first solid evidence associating a specific
gene with a specific chromosome came from
Thomas Hunt Morgan, an embryologist
• Morgan’s experiments with fruit flies
provided convincing evidence that
chromosomes are the location of Mendel’s
heritable factors
Correlating Behavior of a Gene’s Alleles with
Behavior of a Chromosome Pair
• In one experiment, Morgan mated male flies with white
eyes (mutant) with female flies with red eyes (wild
type)
– The F1 generation all had red eyes
– The F2 generation showed the 3:1 red:white eye
ratio, but only males had white eyes
• Morgan determined that the white-eyed mutant allele
must be located on the X chromosome
• Morgan’s finding supported the chromosome theory of
inheritance
CONCLUSION
P
Generation
w+
X
X

w+
X
Y
w
Eggs
F1
Generation
Sperm
w+
w+
w+
w
w+
Eggs
F2
Generation
w
w+
Sperm
w+
w+
w
w
w
w+
44 +
XY
44 +
XX
Parents
22 +
22 +
or Y
X
Sperm
+
44 +
XX
or
22 +
X
Egg
44 +
XY
Zygotes (offspring)
(a) The X-Y system
22 +
XX
22 +
X
76 +
ZW
76 +
ZZ
32
(Diploid)
16
(Haploid)
(b) The X-0 system
(c) The Z-W system
(d) The haplo-diploid system
Early embryo:
X chromosomes
Two cell
populations
in adult cat:
Allele for
orange fur
Allele for
black fur
• In mammalian
females, one of the
two X chromosomes
Cell division and
in each cell is
X chromosome
randomly inactivated
inactivation
during embryonic
Active X
development
Inactive X
• The inactive X
condenses into a
Black fur
Orange fur
Barr body
Active X
• If a female is
heterozygous for a
particular gene
located on the X
X Inactivation in
chromosome, she will
Female Mammals
be a mosaic for that
character
Alterations of Chromosome
Structure
• Breakage of a chromosome can lead to four
types of changes in chromosome structure:
–
–
–
–
Deletion removes a chromosomal segment
Duplication repeats a segment
Inversion reverses a segment within a chromosome
Translocation moves a segment from one
chromosome to another
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
(a)
(b)
(c)
(d)
A B C D E
F G H
A B C D E
F G H
A B C D E
F G H
A B C D E
F G H
Deletion
Duplication
A B C E
F G H
A B C B C D E
Inversion
A D C B E
R
F G H
M N O C D E
Reciprocal
translocation
M N O P Q
F G H
A B P Q
R
F G H
DNA Technology
TRANSFORMATION
Protein Synthesis
• The making of Proteins!
• DNA carries the
“blueprints” for the
making of every
molecule and cellular
structure.
• Transcription
• Translation