When Heredity Does Not Follow Mendelian Rules

Complex Patterns of HeredityIncomplete Dominance

R R

R'

R' RR

RR

R'R'

R'R'

Neither phenotypes is completely dominant

R = RedR = Red

RR'' = White = White

RRRR'' = Pink = Pink

RR = RedRR = Red

RR''RR'' = White = White

Incomplete Dominance

R

R

R'

R’

R

R

RR

R'R'

R'

R'

Neither phenotypes is completely dominant

R = RedR = Red

RR'' = White = White

RR = RedRR = Red

RR''RR'' = White = White

RRRR'' = Pink = Pink

Codominance

Both possible phenotypes can be expressed

R

R

R'

R’

R

R

RR

R'R'

R'

R'

Both phenotypes are expressed in heterozygotes

R = RedR = RedRR'' = White = White

RR = RedRR = Red

RR''RR'' = White = White

RRRR'' = Spotted = Spotted StripedStriped CheckeredCheckered Etc.Etc.

Multiple Phenotypes from Multiple AllelesTraits controlled by multiple alleles

B

b

B

b

B

B

bB

bb

b

B

B = Blue FeathersB = Blue Feathers

b = Chocolate Feathersb = Chocolate Feathers

BBAA = Ash-red Feathers = Ash-red Feathers

B dominant to bB dominant to b

B recessive to BB recessive to BAA

b recessive to Bb recessive to B

b recessive to Bb recessive to BAA

Multiple Phenotypes from Multiple AllelesTraits controlled by multiple alleles

BA

b

B

b

B

BA

bBA

bb

b

B

Multiple Phenotypes from Multiple AllelesTraits controlled by multiple alleles

BA

B

B

b

B

BA

BBA

bb

B

B

Multiple Phenotypes from Multiple AllelesTraits controlled by multiple alleles

BA

BA

b

b

BA

BA

BABA

bb

b

b

Sex Determination22 Pairs of Homologous Chromosomes: Autosomes

X

X

Y

X

X

X

XX

YX

Y

X

1 Pair of Sex Chromosomes

Sex Linked InheritanceTraits located on sex chromosomes: Sex-linked

traits

Xr

XR

Y

XR

XR

Xr

XRXr

YXR

Y

XR

XXRR = Red Eyes = Red Eyes

XXrr = White Eyes = White Eyes

Males = ½ Red EyesMales = ½ Red Eyes

Males = ½ White EyesMales = ½ White Eyes

Females = All Red EyesFemales = All Red Eyes

Polygenic InheritanceTraits controlled by multiple genes

AA BB CC

AA BB CC

aa bb cc

aa bb cc

AAAABB BB CCCC AAaaBB bb CC cc

AAaaBB bbCCcc aaaa bb bb cc cc

Sickle-Cell Disease

H

H'

H

H’

H

H

H'H

H'H'

H'

H

Codominance

Sickle-Cell Disease

H

H'

H’

H'

H'

H

H'H

H'H'

H'

H'

Sickle-Cell Disease

H

H’

H’

H’

H’

H

H’H

H’H’

H’

H’

Multiple Alleles and Blood Type

Multiple Alleles and Blood Type

Multiple Alleles and Blood Type

Sex-Linked Traits in Humans

Color Blindness

XR XG

XR XG

Xr Xg

Y

XR XG XR XG

XR XG Xr Xg Xr Xg

Y

Y

XR XG

Sex-Linked Traits in Humans

Hemophilia: 1:10,000 males1:100,000,000 females

XH

Xh

Y

XH Y

Y

XH

XH Xh Xh

XH

XH

Sex-Linked Traits in Humans

Hemophilia: 1:10,000 males1:100,000,000 females

Xh

Xh

Y

XH Y

Y

Xh

XH Xh Xh

Xh

XH

Sex-Linked Traits in Humans

Hemophilia: 1:10,000 males1:100,000,000 females

Xh

Xh

Y

XH Y

Y

Xh

XH Xh Xh

Xh

XH

Sex-Linked Traits in Humans

Hemophilia: 1:10,000 males1:100,000,000 females

Xh

Xh

Y

Xh Y

Y

Xh

Xh Xh Xh

Xh

Xh

Changes in Chromosome Numbers in Humans

46

23 23

Meiosis, Anaphase (normal)

Changes in Chromosome Numbers in Humans

46

23 23

Fertilization

Normal

Changes in Chromosome Numbers in Humans

46

24 22

Meiosis, Anaphase

Down Syndrome: Trisomy 21

Changes in Chromosome Numbers in Humans

47

24 23

Fertilization

Changes in Chromosome Numbers in Humans

45

22 23

Fertilization

Abnormal Number of Sex Chromosomes

Sex Determination22 Pairs of Homologous Chromosomes: Autosomes

X

XX

Y

XXX

YX

Y

Result of Non-disjunction

X X

Trisomy(21) Down Syndrome

Monosomy: Turner Syndrome

Hexapoid: Wheat

Trisomy(13) Patau’s Syndrome

Triploid: Apples

Polyploid: chrysanthamums

Tool of Genetics

Punnett Square

Pedigree

Karotype

DNA Fingerprinting