The document discusses non-Mendelian genetics, detailing concepts such as incomplete dominance, codominance, multiple alleles, polygenic traits, and sex-linked traits. It includes examples and explanations of how these genetic principles differ from traditional Mendelian inheritance, illustrating with case studies like flower color in plants and blood types in humans. The document also provides problems and sample crosses to reinforce understanding of these genetic concepts.

1. Non-Mendelian Genetics
Objective: To know and understand how nonmendelian genetics work!!

2. Mendelian Genetics:
Dominant & Recessive Review
❖One allele is DOMINANT over the other
(because the dominant allele can “mask” the
recessive allele)
genotype: PP
phenotype: purple
genotype: pp
phenotype: white
genotype: Pp
phenotype: purple

3. Review Problem:
Dominant & Recessive
❖In pea plants, purple flowers (P) are dominant over
white flowers (p). Show the cross between two
heterozygous plants.
P
p
P p
pp
Pp
Pp
PP
- PP (25%)
Pp (50%)
pp (25%)
- ratio 1:2:1
- purple (75%)
white (25%)
- ratio 3:1
GENOTYPES:
PHENOTYPES:

4. Non-Mendelian Genetics
❖Incomplete Dominance
❖Codominance
❖Multiple Alleles
❖Polygenic Traits
❖Sex-Linked Traits

5. Incomplete Dominance
❖a third (new) phenotype
appears in the heterozygous
condition as a BLEND of the
dominant and recessive
phenotypes. Ex - Dominant Red (R) + Recessive White
(r) = Hybrid Pink (Rr)
RR = red rr = white Rr = pink

6. Problem:
Incomplete Dominance
❖Show the cross between a pink and a white flower.
- RR (0%)
Rr (50%)
rr (50%)
- ratio 1:1
- pink (50%); white (50%)
- ratio 1:1
R r
r
r
rr
Rr
rr
Rr
GENOTYPES:
PHENOTYPES:

7. Codominance
❖ in the heterozygous condition, both alleles are expressed equally with NO
blending! Represented by using two DIFFERENT capital letters.
❖ Example: Dominant Black (B) + Dominant White (W) = Speckled Black
and White Phenotype (BW)
❖ Sickle Cell Anemia -
NN =
normal cells
SS = sickle cells NS = some of
each

8. Codominance Example:
Speckled Chickens
❖ BB = black feathers
❖ WW = white feathers
❖ BW = black & white speckled feathers
❖ Notice –
NO GRAY!
NO BLEND!
Each feather is
either black or white

9. Codominance Example:
Rhodedendron
❖R = allele for red flowers
❖W = allele for white flowers
❖Cross a homozygous red
flower with a homozygous
white flower.

10. Codominance Example:
Roan cattle
❖cattle can be
red
(RR – all red hairs)
white
(WW – all white hairs)
roan
(RW – red and white hairs together)

11. Codominance Example:
Appaloosa horses
❖Gray horses (GG) are codominant to white horses
(WW). The heterozygous horse (GW) is an Appaloosa
(a white horse with gray spots).
❖Cross a white horse with an appaloosa horse.
W W
G
W
GW
GW
WW
WW

12. Problem:
Codominance
❖Show the cross between an individual with
sickle-cell anemia and another who is a carrier
but not sick.
N S
S
S
NS
NS
SS
SS
- NS (50%)
SS (50%)
- ratio 1:1
- carrier (50%)
sick (50%)
- ratio 1:1
GENOTYPES:
PHENOTYPES:

13. Multiple Alleles
❖there are more than two alleles for a gene.
Ex – blood type consists of two dominant and
one recessive allele
options. Allele A
and B are
dominant over
Allele O (i)

14. Multiple Alleles:
Lab Mouse Fur Colors
❖Fur colors (determined by 4 alleles):
black agouti yellow

15. Multiple Alleles:
Rabbit Fur Colors
❖Fur colors (determined by 4 alleles):
full, chinchilla, himalayan, albino

16. Multiple Alleles:
Blood Types (A, B, AB, O)
❖Rules for Blood Types:
A and B are co-dominant (Both show)
AA or IA
IA
= type A
BB or IB
IB
= type B
AB or IA
IB
= type AB
A and B are dominant over O (Regular dom/rec)
AO or IA
i = type A
BO or IB
i = type B
OO or ii = type O

17. Multiple Alleles:
Blood Types (A, B, AB, O)

18. Phenotype
Possible
Genotype(s)
Allele
(antigen)
on RBC
surface
Can
Donate
Blood To
Can
Receive
Blood
From
A
IA
i
IA
IA
A A, AB A, O
B
IB
i
IB
IB
B B, AB B, O
AB IA
IB
AB AB
A, B, AB,
O
O ii O
A, B,
AB, O O

19. Problem:
Multiple Alleles
❖Show the cross between a mother who has type
O blood and a father who has type AB blood.
- Ai (50%)
Bi (50%)
- ratio 1:1
- type A (50%)
type B (50%)
- ratio 1:1
GENOTYPES:
PHENOTYPES:
i i
A
B
Ai
Bi
Ai
Bi

20. Problem:
Multiple Alleles
❖Show the cross between a mother who is heterozygous for
type B blood and a father who is heterozygous for type A
blood.
-AB (25%); Bi (25%);
Ai (25%); ii (25%)
- ratio 1:1:1:1
-type AB (25%); type B (25%)
type A (25%); type O (25%)
- ratio 1:1:1:1
GENOTYPES:
PHENOTYPES:
A i
B
i
AB
ii
Bi
Ai

21. Polygenic Traits
❖traits produced by multiple genes
❖example: skin color

22. Sex-Linked Traits
❖Gene is attached to
the X chromosome
only, not found on
the Y chromosome
at all. (women have
XX, men have XY
chromosomes).
These disorders are
more common in
boys.
❖examples: red-green
colorblindness

23. Sex-Linked Traits
❖in males, there is
no second X
chromosome to
“mask” a recessive
gene. If they get an
X with the disorder,
they have it. Girls
must inherit
defective X’s from
both parents.

25. Sex-Linked Traits
A: 29, B: 45, C: --, D: 26
→ Normal vision
A: 70, B: --, C: 5, D: --
→ Red-green color blind
A: 70, B: --, C: 5, D: 6
→ Red color blind
A: 70, B: --, C: 5, D: 2
→ Green color blind