Honors
Biology
Ch. 11
Complex Inheritance
and Human Heredity
I. Human Inheritance
- heredity in humans is the same as in
other organisms
- most genetic diseases are recessive
and rare
A. Recessive Traits
- diseases caused by a single
defective gene/protein
1. Cystic Fibrosis (CF)
2. Tay-Sachs Disease
3. Albinism
4. Phenylketonuria (PKU)
5. Sickle-Cell Anemia
DISORDER
OCCURRENCE
IN THE U.S.
CAUSE
EFFECT
CURETREATMENT
Cystic
Fibrosis
1 : 3500
(Mainly
people of
northern
European
descent)
The gene that
codes for a
membrane
protein is
defective.
*Excessive
Mucus
Production
*Digestive and
Respiratory
Failure
*No Cure
*Daily
Cleaning of
Mucus from
Lungs
*Mucusthinning
Drugs
Albinism
1 : 17,000
Genes do not
produce
melanin.
*No Color in
Skin, Eyes &
Hair
*Prone to Skin
Cancer and
Cataracts
*No Cure
*Protect Skin
from the
Sun
Tay-Sachs 1 : 2500
Disease
(Affects
People of
Jewish
descent)
Absence of a
necessary
enzyme that
breaks down
fatty
substances
*Buildup of Fatty
Deposits in The
Brain
*Mental
Disabilities
*No Cure or
Treatment
*Death
Occurs by
Age 5
B. Dominant Traits
1. Huntington’s Disease
- rare, degenerative nervous
system disorder
Woody Guthrie
2. Achondroplasia
- a disorder of
bone growth
- homozygous
dominant
condition is fatal
3. Polydactyly
II. Other Inheritance
Patterns
A. Sex Chromosomes:
- pair of chromosomes that
determine an individual’s sex
XX - female XY - male
Autosomes: the other
chromosome pairs except the
sex chromosomes
Human Chromosomes:
44 Autosomes
Human Chromosomes:
2 Sex Chromosomes
B. Sex-Linked Traits:
- trait controlled by a recessive allele
on the "X" sex chromosome
- more common in males
- Ex. Red-green color-blindness,
hemophilia
Can you see a number?
Queen Victoria’s Family
Pedigree of Europe’s Royal Families
C. Sex-Influenced Traits:
- trait controlled by an allele that is
recessive in females and dominant in
males
- Ex.
Male-pattern
Baldness
D. Incomplete Dominance:
- a trait in which the heterozygote
shows a blending of traits
- Ex. Carnations and Snap dragons:
R - red, W - white, RW - pink
Incomplete Dominance: P
Homozygous
Red Parent
R
RW
Homozygous
White Parent
Pink
R
RW
Pink
RW
RW
Pink
Pink
Incomplete Dominance: F1
Heterozygous
Pink Parent
R
RR
Heterozygous Pink
Parent
W
RW
Red
Pink
RW
WW
Pink
White
E.Codominance:
- a trait in which the heterozygote
shows both alleles equally
- Ex. Horses:
R - red, W - white, RW - roan
- Ex. ABO Blood Groups
A B AB
E.Codominance:
Roan Horses
E.Codominance:
ABO Blood Groups
F. Multiple Alleles:
1. ABO Blood Groups:
- 4 blood types: A, B, AB, O
- caused by a protein in the
membranes of red blood cells
- 3 alleles for this protein:
IA, IB, i
- Genotypes for the 4 blood types:
Type
Type
Type
Type
A:
B:
AB:
O:
IA IA, IAi
IB IB, IBi
IA IB
Universal Recipient
ii
Universal Donor
Human Blood Types
2. Rh Blood Groups:
- an example of multiple alleles
- there are about 8 dominant alleles (+)
- one recessive allele (-)
Blood Type - Donors
and Recipients
% Blood Types in the U. S.
G. Epistasis
- A gene at one locus alters the
phenotypic expression of a gene at a
second locus.
- Example:
black,
chocolate,
and golden
fur color in
Labrador
retrievers
Epistasis: Black, Chocolate, and
Golden Labrador Retrievers
Epistasis: Black, Chocolate, and
Golden Labrador Retrievers

BbEe
BbEe
Sperm
Eggs
1⁄
4
BE
1⁄
4
bE
1⁄
4
Be
1⁄
4
be
1⁄
4
BE
1⁄
4
bE
Be
1⁄
4
1⁄
4
BBEE
BbEE
BBEe
BbEe
BbEE
bbEE
BbEe
bbEe
BBEe
BbEe
BBee
Bbee
BbEe
bbEe
Bbee
bbee
9⁄
16
3⁄
16
4⁄
16
be
Epistasis: Black, Chocolate, and
Golden Labrador Retrievers
Epistasis: Black, Brown,
and White Coat in Mice

BbCc
BbCc
Sperm
1⁄
BC
4
1⁄
4
bC
1⁄
4
1⁄
Bc
4
bc
Eggs
1⁄
1⁄
4
BC
BBCC
BbCC
BBCc
BbCc
4
bC
BbCC
bbCC
BbCc
bbCc
1⁄
1⁄
4
Bc
BBCc
BbCc
BBcc
4
bc
BbCc
bbCc
Bbcc
9⁄
16
3⁄
16
Bbcc
4⁄
bbcc
16
H. Polygenic Inheritance:
- traits controlled by more than one
pair of genes
- Ex. hair, skin, and eye color
EGGS
Mother
AaBb
Human
Eye
Color
AB
Ab
aB
ab
black
dark brown
dark brown
light brown
AABB
AABb
AaBB
AaBb
dark brown
light brown
light brown
blue
AAbB
AAbb
AabB
Aabb
dark brown
light brown
light brown
blue
aABB
aABb
aaBB
aaBb
light brown
blue
blue
light blue
aABb
aABb
aaBb
aabb
AB
Father
AaBb
SPERM
Ab
aB
ab
Human Skin Color
III. Nondisjunction:
- homologous chromosomes fail to
separate during meiosis
III. Nondisjunction:
-
Down Syndrome (Trisomy 21)
Klinefelter’s Syndrome (XXY)
XYY Syndrome
Turner’s Syndrome (Monosomy X) (X)
Trisomy X (XXX)
Down syndrome
(Trisomy 21)
Incidence of Down Syndrome
Number per 1000 Births
400
300
200
100
0
10
20
30
40
Age of Mother (years)
50
Turner’s Syndrome (Monosomy X)
XYY Syndrome
Trisomy X (XXX)
Klinefelter’s Syndrome (XXY)
Down Syndrome (Trisomy 21)
Normal Female
Edward’s Syndrome (Trisomy 18)
IV. Fetal Testing:
- Amniocentesis
- Chorionic Villus Sampling
- Ultrasound
Amniocentesis
Ultrasound Image
Head
Head
Body
Body
Ultrasound Of Fetus
The
End
Human Chromosomes
(23 homologous pairs)
Epistasis: Black, Chocolate, and
Golden Labrador Retrievers