Download complex patterns of inheritance

WHAT’S GOING ON HERE???
Multiple Alleles
Codominance
Incomplete Dominance
Sex-Linked Trait
COMPLEX PATTERNS OF
INHERITANCE
When heredity breaks the rules…
INCOMPLETE DOMINANCE
Neither trait is dominant; the heterozygous
individual is a BLEND of the two traits
 Example: In a variety of flowers (known as four
o’clock flowers), crossing a homozygous red flower
with a homozygous white flower makes
heterozygous offspring that are PINK
 Problem:
R = red
R1 = white
R
R
RR1
Parents: RR x R1R1
R1 RR1

Genotype: 4RR1
Phenotype: 4 Pink
R1
RR1
RR1
CODOMINANCE
BOTH alleles are expressed equally at the same
time
 Example: Crossing a homozygous blackfeathered chicken with a homozygous whitefeathered chicken produces a black-and-white
speckled chicken
 Problem:
B = Black feathers
W = White feathers
Parents: BB x WW
Genotype: 4 BW
B
B
BW
BW
Phenotype: 4 black-andW
BW
white speckled
W BW
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MULTIPLE ALLELES
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A trait is controlled by more than two alleles; results in
multiple phenotypes
Example: Blood types in humans – 4 possible phenotypes –
Type A, B, AB, O
Type A and Type B are CODOMINANT; Type O is
RECESSIVE to A and B
Problem: Cross a heterozygous Type B mom and a
heterozygous Type A dad
Parents: IBi x IAi
Phenotype
Possible Genotype
Type A
IAIA or IAi
Type B
IBIB or IBi
IA
IAIB
IAi
Type AB
IAIB
i
IBi
ii
Type O
ii
IB
i
Genotype: 1 IAIB, 1 IAi, 1 IBi, 1 ii
Phenotype: 1 Type AB, 1 Type A, 1 Type B, 1 Type O
SEX LINKED TRAITS
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A trait controlled by a gene found ONLY on the XCHROMOSOME
Each human has 23 pairs of chromosomes
Pairs 1-22 are the same in males and females, and are called
autosomes
 Pair 23 are the sex chromosomes which determine gender
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Females have two homologous X-chromosomes - XX
Males have one X-chromosome (inherited from mom) and one Y-chromosome
(inherited from dad) – XY
Example: the gene for eye color in fruit flies (studied by
Thomas H. Morgan) is found on the X-chromosome; RED is
dominant and WHITE is recessive
Problem: Cross a red-eyed male with a white-eyed female
R = red
r = white
Parents: XRY x XrXr
Xr
Xr
Genotype: 2 XRXr, 2XrY
XR XRXr
XRXr
Phenotype: 2 red-eyed females
r
XrY
2 white-eyed males
Y XY