Familial Hypercholesterolemia
(FH) exhibits semidominant lethality
Genotypes
Prevalence
FF
Most people
Effect
Normal
plasma LDL
level
Fibroblast
+ blood
cells
Normal receptor
numbers
FF?
F?F?
1/500 people
1/1,000,000 people
2 x normal
plasma LDL
level (heart
attacks by 35
years of age,
and 1/20 under 60)
6 x normal
plasma LDL
level (heart
attacks 2-20
years of age)
Fibroblast
+ blood
cells
1/2 normal
receptor numbers
Fibroblast
+ blood
cells
Lacking normal
receptors
Example of Environmental – Genetic interaction
Severity of atherosclerosis in genetically selected birds
(for high blood cholesterol concentration)
Chol added to diet
No chol added to diet
HL
Severe
Moderate
LL
Moderate
Low
Allelic Relationships at three levels in Sickle Cell Anemia
Organism
(overall viability)
Dominance
normal
HbA HbA
normal
HbA Hba
anemia (death)
Hba Hba
Cellular
(RBC shape)
Semi-dominance
normal
HbA HbA
sickle-low O2
HbA HbA'
sickle
HbA' HbA'
Molecular
(hemoglobin type)
1/1 normal
1/1 mutant (S)
Co-dominance
HbA HbA
1/2 normal,
1/2 mutant (S)
HbA HbS
HbS HbS
Penetrance: The percentage of individuals that show a particular
phenotype to any degree among those capable of showing it.
Penetrance is affected by modifier genes, epistatic genes, or
suppressor genes in the rest of an organism’s genome or because
of modifying effects of the environment.
Expressivity: The degree of effect produced by a penetrant
genotype. A trait, although penetrant, may be quite variable
in its expression.
Example of penetrance and expressivity: polydactyly (P),
P_ = polydactylous condition, pp = normal.
Mendel’s Second Law
(Principle of Independent Assortment)
• Either allele of one gene pair can enter a
gamete with either allele of any other gene
pair and all possible combinations are
produced in equal proportions.
DIAGRAM AND SUMMARY OF A CROSS BETWEEN A VARIETY OF GARDEN PEAS WITH YELLOW
ROUND SEEDS AND A VARIETY WITH GREEN, WRINKLED SEEDS. THE F1 x F1 REPRESENTED
ILLUSTRATES A DIHYBRID CROSS.
P
Yellow, Round
Seed Parent
GGWW
Green, Wrinkled
Pollen Parent
ggww
x
GW
F1
gw
Seed Parent
GgWw
Pollen Parent
GgWw
x
GW Gw gW gw
GW Gw gW gw
Male Gametes
F2
Females Gametes
GW
Gw
gW
gw
GW
GW
GW
Gw gW gw
GW GW GW
Gw
GW
Gw
Gw
Gw
gW gw
Gw Gw
gW
GW
gW
Gw
gW
gW gw
gW gW
gw
GW
gw
Gw
gw
gW gw
gw gw
31
Phenotypes
Genotypes
Genotypic Frequency
Yellow, round
GGWW
GGWw
GgWW
GgWw
1
2
2
4
9
Yellow, wrinkled
GGww
Ggww
1
2
3
Green, round
ggWW
ggWw
1
2
3
Green, wrinkled
ggww
1
1
31 cont.
Phenotypic Ratio
P
AA x aa
P BB x bb
F1 Aa x Aa
F1 Bb x Bb
F2 1/4 AA
F2 1/4 BB
P
2/4 Aa 3/4 A_
2/4 Bb 3/4 B_
1/4 aa 1/4 aa
1/4 bb 1/4 bb
AABB x aabb
F1 AaBb x AaBb
F2 3/4 A_ 3/4 B- = 9/16 A_B_
3/4 A_1/4 bb = 3/16 A_bb
1/4 aa 3/4 B_ = 3/16 aaB_
1/4 aa 1/4 bb = 1/16 aabb
34
or
F2
AABB 1
AABb 2
9 A_B_
AaBB 2
AaBb 4
AAbb 1
3 A_bb
Aabb 2
aaBB 1
3 aaB_
aaBb 2
aabb 1
1 aabb
34 cont.
GENETYPIC RATIOS: Using the Forked-Line Method
1DD
2 Dd
1 dd
1 GG
1 DDGG
2 Gg
2 DDGg
1 gg
1 DDgg
1 GG
2 DdGG
2 Gg
4 DdGg
1 gg
2 Ddgg
1 GG
1 ddGG
2 Gg
2 ddGg
1 gg
1 ddgg
PHENOTYPIC RATIOS: Using the Forked-Line Method
3 G_
9 Tall Yellow
1 gg
3 Tall Green
3 G_
3 Dwarf Yellow
1 gg
1 Dwarf Green
3 D_
1 dd
35
Diagram and summary illustrating a method for solving a testcross type problem
involving two gene pairs. This cross is between an F1 garden pea with yellow, round
seeds and the full recessive parent type with green, wrinkled seeds.
F1 Parent
Testcross Parent
Yellow, Round
Green, Wrinkled
Seed Parent
GgWw
Pollen Parent
ggww
GW Gw gW gw
GW
gw
GgWw
gw
Gw
Ggww
38
Gametes
gW
gw
ggWw
ggww
Phenotypes
Genotypes
Genotypic Frequency
Yellow, round
GgWw
1
1
Yellow, wrinkled Ggww
1
1
Green, round
ggWw
1
1
Green, wrinkled ggww
1
1
38 cont.
Phenotypic Ratio
Using the information given, fill in all blanks below. Circle each gamete. A dihybrid cross for
two autosomal traits in Pisum sativum. G = yellow, g = green; W = round, w = wrinkled.
P Phenotypes
Genotypes
Gametes
Yellow, round
GGWW
Green, wrinkled
ggww
.
.
x
x
x
F1 Phenotypes
Genotypes
Gametes
F2
F2
F2
F2
x
x
x
.
.
.
Genotypes
Phenotypes
Phenotypic ratio
Genotypic ratio
.
.
.
.
USE THE INFORMATION ABOVE TO MAKE A TESTCROSS BELOW.
F1 Parent
Phenotypes
Genotypes
Gametes
Testcross Parent
x
x
x
Testcross Progeny
Phenotypes
Genotypes
______________ ______________ ______________ ____________
Testcross Phenotypic Ratio
Testcross Genotypic Ratio
39
Using the information given, fill in all blanks below. Circle each gamete. A dihybrid cross for
two autosomal traits in Pisum sativum. G = yellow, g = green; W = round, w = wrinkled.
P Phenotypes
Genotypes
Gametes
x
x
x
Yellow, round
GGWW
1/1 GW
x
x
x
F1 Phenotypes
Yellow, round
Genotypes
GgWw
Gametes
1/4 GW 1/4 Gw 1/4 gW 1/4 gw
F2
F2
F2
F2
Green, wrinkled
ggww
1/1 gw
.
.
.
Yellow, round
GgWw
1/4 GW 1/4 Gw 1/4 gW 1/4 gw
Genotypes
32 = 9, (1+2+1)2
Phenotypes
22 = 4, (3+1)2 9/16 G-W- 3/16 G-ww 3/16 ggW- 1/16 ggww
Phenotypic ratio
9:3:3:1
Genotypic ratio
4:2:2:2:2:1:1:1:1
.
.
.
.
.
.
USE THE INFORMATION ABOVE TO MAKE A TESTCROSS BELOW.
Phenotypes
Genotypes
Gametes
.
F1 Parent
Yellow, round
x
x
GgWw
1/4 GW 1/4 Gw 1/4 gW 1/4 gw x
Testcross Parent
Green, wrinkled
ggww
1/1 gw
.
.
.
Testcross Progeny
Phenotypes
Yellow, round
Green, round
Yellow, wrinkled Green, wrinkled
Testcross Phenotypic Ratio
Testcross Genotypic Ratio
GgWw
Ggww
1:1:1:1
1:1:1:1
39
Genotypes
ggWw
ggww
.
.
Using the information given, fill in all blanks. Circle each gamete. A dihybrid cross for two
autosomal traits in Pisum sativum. G = yellow, g = green; W = round, w = wrinkled.
P Phenotypes
Genotypes
Gametes
Yellow, wrinkled
GGww
F1 Phenotypes
Genotypes
Gametes
F2
F2
F2
F2
x
x
x
Green, round
ggWW
.
.
x
x
x
.
.
.
Genotypes
Phenotypes
Phenotypic ratio
Genotypic ratio
.
.
.
.
USE THE INFORMATION ABOVE TO MAKE A TESTCROSS BELOW.
F1 Parent
Phenotypes
Genotypes
Gametes
Testcross Parent
x
x
x
.
.
.
Testcross Progeny
Phenotypes
Genotypes
.
Testcross Phenotypic Ratio
.
Testcross Genotypic Ratio
.
40
Using the information given, fill in all blanks. Circle each gamete. A dihybrid cross for two
autosomal traits in Pisum sativum. G = yellow, g = green; W = round, w = wrinkled.
P Phenotypes
Genotypes
Gametes
Yellow, wrinkled x
x
GGww
1/1 Gw
x
Green, round
ggWW
1/1 gW
F1 Phenotypes
Yellow, round
Genotypes
GgWw
Gametes
1/4 GW 1/4 Gw 1/4 gW 1/4 gw
F2
F2
F2
F2
.
.
.
x
x
x
Yellow, round
GgWw
1/4 GW 1/4 Gw 1/4 gW 1/4 gw
Genotypes
32 = 9, (1+2+1)2
Phenotypes
22 = 4, (3+1)2 9/16 G-W- 3/16 G-ww 3/16 ggW- 1/16 ggww
Phenotypic ratio
9:3:3:1
Genotypic ratio
4:2:2:2:2:1:1:1:1
Phenotypes
Genotypes
Gametes
Testcross Parent
Green, wrinkled
ggww
1/1 gw
GgWw
Ggww
40
Genotypes
ggWw
ggww
.
.
.
.
.
.
.
Testcross Progeny
Phenotypes
Yellow, round
Green, round
Yellow, wrinkled Green, wrinkled
Testcross Phenotypic Ratio
1:1:1:1
Testcross Genotypic Ratio
1:1:1:1
.
.
USE THE INFORMATION ABOVE TO MAKE A TESTCROSS BELOW.
F1 Parent
Yellow, round
x
GgWw
x
1/4 GW 1/4 Gw 1/4 gW 1/4 gw x
.
.
.