Appearance:
P Generation
Genetic makeup:
Gametes
F1 Generation
Appearance: Genetic makeup:
Gametes:
F2 Generation
Purple flowers Pp
P p 1 2 1 2
P p
F1 sperm
F1 eggs PP Pp
Pp pp
P
p
3 : 1
Purple flowers
PP
White flowers
pp
P p Punnett Square
Phenotype
Purple
Purple 3
Purple
Genotype
PP (homozygous
Pp (heterozygous
Pp (heterozygous
pp (homozygous 1
2
1
Ratio 1:2:1
White
Ratio 3:1
1
Segregation of alleles into eggs
Rr
Sperm
R r
R
r R
R
R
r
Eggs
r R
r
r
Segregation of alleles into sperm
Rr
1 2
1 2
1 4
1 4
1 4
1 4
1 2
1 2
Segregation of Albinism
Human Disorders
Autosomal Recessive:
Albinism
Cystic fibrosis
Sickle Cell Anemia
Tay Sachs Disease
Inherited Deafness
Autosomal Dominant:
Achondroplasia
Familial hypercholesterolemia
Huntington’s Disease
Marfan syndrome
P Generation
F1 Generation
YYRR
Gametes YR yr
yyrr
YyRr Hypothesis of dependent assortment
Hypothesis of independent assortment
Sperm Eggs
YR
Yr
yr YR
YR
yr
Eggs
YYRR YyRr
YyRr yyrr yR
yr Phenotypic ratio 3:1
F2 Generation (predicted offspring)
YYRR YYRr YyRR YyRr
YYRr YYrr YyRr Yyrr
YyRR YyRr yyRR yyRr
YyRr Yyrr yyRr yyrr
Phenotypic ratio 9:3:3:1
YR Yr yR yr
Sperm
1 2 1 4
1 4
1 4
1 4
1 4 3 4
1 2
1 2
1 2
1 4
9 16 3 16 3 16 3 16
1 4 1 4 1 4
Law of Independent Assortment
Meiosis I
Metaphase II
Gametes
AaDd AaDd
AD Ad aD ad
AD
Ad
aD
ad
AADD Pigment Hearing
aadd Albino Deaf
AADd Pigment Hearing
AaDD Pigment Hearing
AaDd Pigment Hearing
AADd Pigment Hearing
AAdd Pigment
Deaf
AaDd Pigment Hearing
Aadd Pigment
Deaf
AaDD Pigment Hearing
AaDd Pigment Hearing
aadd Albino Hearing
aaDd Albino Hearing
AaDd Pigment Hearing
Aadd Pigment
Deaf
aaDd Albino Hearing
Dihybrid Cross Eye Color Incomplete Dominance
! The expression of a phenotype that is intermediate to those of the parents • R1R1 (red) x R2R2 (white) ! R1R2 (pink)
Example: Sickle Cell Anemia in Humans
Multiple Alleles, Codominant Alleles Genes Can Interact to Produce Phenotypes
! Epistasis • A form of gene interaction in which one gene
masks or prevents expression of another gene • Example: Bombay gene (h) can block expression
of blood types A and B