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BIOLOGY
Chapter 11: pp. 189 - 210
10th Edition
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Parents
TT
Ee
tt
Ee
t
T
eggs
E
e
Tt
eggs
Ee
e
T
t
T
sperm
EE
Punnett square
E
spem
Sylvia S. Mader
Mendelian Patterns of
Inheritance
TT
Tt
Tt
tt
t
Ee
Offspring
ee
Offspring
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display
1
2
• 3.A.3: The chromosomal basis of inheritance provides an
understanding of the pattern of passage (transmission) of
genes from parent to offspring.
3
Gregor Mendel
• Austrian monk
• University of Vienna
• Conducted breeding experiments
with the garden pea
• Formulated fundamental laws
of heredity in early 1860s
• Had no knowledge of cells or
chromosomes
• Did not have a microscope
1.
hybrid- offspring of 2 genetically different parents (tall
w/short)
YY
2.
X
yy
=
Yy
phenotype- outward appearance of a char. (brown
hair, yellow pea)
3. genotype- genetic make up of an organism (Tt, RR)
Tt produces tall plant
Tt is genotype
tt produces short plant
tt is genotype
4. homozygous- alleles in a pair are identical (TT, rr)
Parents (P): TT x tt (tall & short)
5. heterozygous- alleles in a pair are different (Tt, Rr)
Offspring (F1): Tt (all tall)
6. recessive- trait doesn’t show up unless both alleles
are lower case letter.
i.e. blue eyes, short plant
7. dominant- trait shows up as long as 1 of alleles is
upper case letter.
i.e. brown eyes, tall plant
8. co-dominant- both letters get to show. i.e. blood
typing (i, IA, IB ) (IAIB = AB blood type)
The Blood
Blood Types- genetic alleles determine your blood type: IA,
IB, or i.
a. If you have IAIA or IAi, your blood type is A, IBIB or IBi is
blood type B, ii is blood type O, and IAIB is AB.
A
B
Antigens determine blood type. They
stimulate an immune response. Body
produces antibodies to combat
antigens. (only for the other blood
types however)
Universal
Donor?
Universal
Receiver?
The Blood
Rhesus factor (Rh factor)- Rh+ if you have Rh antigen on
RBC. If Rh- mother is pregnant w/ Rh+ baby can
complicate next pregnancy.
9. Punnett square- chart used to solve genetic
problems, to predict genotypes and phenotypes (must
know genotypes of parents)
• Monohybrid cross- Looking at 1 trait.
Sperm Cell Possibilities
Egg
Cell
Possibilities
T
T
t
Tt
Tt
t
Tt
Tt
Possible
Offspring &
Probability
Mendel’s Monohybrid Crosses:
An Example
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
P generation
TT
P gametes
tt
T
t
F1 generation
Tt
F1 gametes
T
t
F2 generation
sperm
T
TT
Tt
Tt
tt
t
Offspring
Allele Key
T = tall plant
t = short plant
Phenotypic Ratio
3
1
tall
short
11
10. Incomplete Dominance- when 1 phenotype is not
dominant over the other. Heterozygote shows a
“blended” trait.
11. Sex-Linked Traits- traits on only the X or Y (sex)
chromosome. (Hemophilia, colorblindness– both on
the X chromosome)
XY means
male. X
from mom.
Y from dad.
XX means
female. X
from mom.
X from dad.
Laws of Genetics
1.
Law of unit factors- he deduced that there are
units in the cell (now know them as genes) that
determine the trait and they come in pairs (1 from
each parent).
Laws of Genetics
2. Law of segregation- gene pairs (alleles) are separated
during gamete formation. Gametes have ½ # of
chromosomes or alleles as parent has.
Laws of Genetics
3. Law of dominance- one trait appears whenever an
allele for that trait exists (dominant trait - uppercase)
and one trait will only be exhibited if there are two alleles
for it (recessive trait – lower case).
• A test cross can be used to discover the genotype of
a plant with a dominant trait. Example: tall plant, not
sure if it is TT or Tt. Cross-pollinate w/ a homozygous
recessive (tt) short plant. If all offspring are tall, then
parent plant is TT.
T
?
T
?
t
t
tall
short
t
t
tall
short
Laws of Genetics
4. Law of independent assortment- genes for different
traits (flower color & height) are inherited independently of
one another. If genotype is RrYy, R and r will separate
from each other as well as from Y and y
* Mendel’s experiments w/ dihybrid crosses (differ in 2
traits) led him to the last law.
Dihybrid Crosses
• Dihybrid cross
• Predictions of crosses are based on probability (dividing #
of desired outcomes by total # of outcomes)
• i.e. 1 in 2 chance of flipping heads on a quarter
YS
Ys
YS
Ys
yS
ys
Dihybrid Inheritance
yS
ys
• Some genes are present on the X chromosome and absent
from the shorter Y chromosome in humans.
• These are sex linked traits.
• Click4Biology: theoretical genetics
• Sex Linkage refers to genes that are on the X chromosome
(which is larger than the Y chromosome). Females are more
apt to avoid a recessive trait, since they have 2 X
chromosomes.
• Color blindness and hemophilia are sex linked traits.
• Free biology Animations (the Romanovs)
• Sex Linked Traits
• Females can be homozygous or heterozygous with
respect to sex-linked genes.
• Female carriers are heterozygous for X-linked recessive
alleles.
• Colorblindness- Xe
• Female not colorblind- XE XE ; XE Xe (carrier)
• Female colorblind- Xe Xe
• Male not colorblind- XE Y
• Male colorblind- Xe Y
*Males have 1 X therefore they will be colorblind if they get
the recessive from their mother. If they get the dominant
from mom they will not.
*If the observed distribution is the same for M & F, then
the trait is probably NOT sex-linked. If not then – Sex
Linked.
25
X – Linked Inheritance
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P generation
XrY
P gametes
Xr
XRXR
XR
Y
F1 generation
XRY
XRXr
eggs
XR
F1 gametes
Xr
F2 generation
sperm
XR
XRXR
XRXr
XRY
XrY
Y
Offspring
Allele Key
XR = red eyes
Xr = white eyes
Phenotypic Ratio
females:
males : 1
1
all red-eyed
red-eyed
white-eyed
Distribution is
different for M & F.
Sex-linked?
Autosomal?
26
Chi square test
• F1 gen= Red eye Female (XRXr) x Red eye Male (XRY)
• F2 gen (predicted)= Female-50 red eye; Male-25 red, 25 white
• F2 gen (actual)= 51 red F; 26 red M; 23 white M
• Ʃ (o-e)2/ e = (51-50)2 / 50 + (26-25)2 / 25 + (23-25)2 / 25
= 1/50 + 1/25 + 4/25 = 11/50= 0.22
df (# outcomes – 1)= 2
.05= 5.991
0.22 < 5.991, Accept null hypothesis! No statistical difference
observed/expected!
Chi-squared Test – YouTube
27
X-Linked Recessive Pedigree
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XbY
XBXB
XBY
XBXb
daughter
grandfather
XBY
XbXb
XbY
XBY
XBXB
XBXb
Xb Y
grandson
XBXB
XBXb
XbXb
XbY
XbY
Key
= Unaffected female
= Carrier female
= Color-blind female
= Unaffected male
= Color-blind male
X-Linked Recessive
Disorders
• More males than females are affected.
• An affected son can have parents who have the
normal phenotype.
• For a female to have the characteristic, her father must
also have it. Her mother must have it or be a carrier.
• The characteristic often skips a generation from the
grandfather to the grandson.
• If a woman has the characteristic, all of her sons will
have it.
• 3.A.4: The inheritance pattern of many traits cannot be
explained by simple Mendelian genetics.
• 4.C.2: Environmental factors influence the expression of
the genotype in an organism.
• Pedigrees!
29
Human Genetic Disorders
• Genetic disorders are medical conditions caused by
alleles inherited from parents
• Autosome - Any chromosome other than a sex
chromosome (X or Y)
• Genetic disorders caused by genes on autosomes are
called autosomal disorders
• Some genetic disorders are autosomal dominant
• An individual with AA has the disorder
• An individual with Aa has the disorder
• An individual with aa does NOT have disorder
• Other genetic disorders are autosomal recessive
• An individual with AA does NOT have disorder
• An individual with Aa does NOT have disorder, but is a carrier
• An individual with aa DOES have the disorder
• Mendelian Genetics
30
Autosomal Recessive Pedigree Chart
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
I
II
III
IV
aa
A?
A?
Aa
Aa
Aa
*
Aa
aa
aa
A?
A?
A?
A?
Key
aa = affected
Aa = carrier (unaffected)
AA = unaffected
A? = unaffected
Autosomal recessive disorders
(one allele unknown)
• Most affected children have unaffected
parents.
• Heterozygotes (Aa) have an unaffected phenotype.
• Two affected parents will always have affected children.
• Close relatives who reproduce are more likely to have
affected children.
• Both males and females are affected with equal frequency.
31
Autosomal Dominant Pedigree Chart
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Aa
Aa
I
*
II
III
Aa
aa
Aa
Aa
aa
A?
aa
aa
aa
aa
aa
aa
Key
AA = affected
Aa = affected
A? = affected
(one allele unknown)
aa = unaffected
Autosomal dominant disorders
• affected children will usually have an
affected parent.
• Heterozygotes (Aa) are affected.
• Two affected parents can produce an unaffected child.
• Two unaffected parents will not have affected children.
• Both males and females are affected with equal frequency.
33
Autosomal Recessive Disorders
• Tay-Sachs Disease
• Progressive deterioration of psychomotor functions
• Cystic Fibrosis
• Mucus in bronchial tubes and pancreatic ducts is
particularly thick and viscous
• Phenylketonuria (PKU)
• Lack enzyme for normal metabolism of phenylalanine
34
Cystic Fibrosis
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H2O
Cl-
Cl-
ClCl-
H2O
H2O
Cl-
nebulizer
defective
channel
percussion
vest
thick mucus
© Pat Pendarvis
35
Methemoglobinemia
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Courtesy Division of Medical Toxicology, University of Virginia
36
Autosomal Dominant Disorders
• Neurofibromatosis
• Tan or dark spots develop on skin and darken
• Small, benign tumors may arise from fibrous nerve coverings
• Huntington Disease
• Neurological disorder
• Progressive degeneration of brain cells
• Severe muscle spasms
• Personality disorders
37
A Victim of Huntington Disease
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
JK
JJ JK
JL
JK
JL KL
a.
JL
JK JK
JL
JL
JL
JJ KL
JJ KL
KL
b.
a: © Steve Uzzell
JJ
KL
JJ
JK JK
JK JK KL
JK JK KL KK KL
KL KL
JL
JJ
38
Pleioptropic Effects
• Pleiotropy
• A gene that affects more than one characteristic of an
individual
• Sickle-cell (incomplete dominance
• Occurs when a single mutant gene affects two or more
distinct and seemingly unrelated traits.
• Marfan syndrome have disproportionately long arms,
legs, hands, and feet; a weakened aorta; poor eyesight
39
Marfan Syndrome
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Connective
tissue defects
Skeleton
Heart and blood vessels
Chest wall deformities
Mitral valve
Long, thin fingers, arms, legs
prolapse
Scoliosis (curvature of the spine)
Flat feet
Long, narrow face
Loose joints
Enlargement
of aorta
Eyes
Lens dislocation
Severe nearsightedness
Aneurysm
Aortic wall tear
(Left): © AP/Wide World Photos; (Right): © Ed Reschke
Lungs
Collapsed lungs
Skin
Stretch marks in skin
Recurrent hernias
Dural ectasia: stretching
of the membrane that
holds spinal fluid
40
Polygenic Inheritance
• Occurs when a trait is governed by two or more
genes having different alleles Polygenetic
Inheritance
• Each dominant allele has a quantitative effect on
the phenotype
• These effects are additive
• Result in continuous variation of phenotypes
41
Frequency Distributions in Polygenic Inheritance
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P generation
Game genetics
F1 generation
F2 generation
Proportion of Population
20
—
64
15
—
64
6
—
64
1
—
64
Genotype Examples
42
• Epistasis
• A gene at one locus interferes with the expression of a
gene at a different locus
• Human skin color (polygenic inheritance)
• 1 gene turns another gene on or off (albino mice)
The “B” “b” gene determines
mouse coat color. If there is
“cc” present the gene “B” will
be turned off and the mouse
is white.